firmware: arm_scmi: Clear stale xfer->hdr.status

[platform/kernel/linux-rpi.git] / drivers / firmware / arm_scmi / driver.c

// SPDX-License-Identifier: GPL-2.0
/*
 * System Control and Management Interface (SCMI) Message Protocol driver
 *
 * SCMI Message Protocol is used between the System Control Processor(SCP)
 * and the Application Processors(AP). The Message Handling Unit(MHU)
 * provides a mechanism for inter-processor communication between SCP's
 * Cortex M3 and AP.
 *
 * SCP offers control and management of the core/cluster power states,
 * various power domain DVFS including the core/cluster, certain system
 * clocks configuration, thermal sensors and many others.
 *
 * Copyright (C) 2018-2021 ARM Ltd.
 */

#include <linux/bitmap.h>
#include <linux/device.h>
#include <linux/export.h>
#include <linux/idr.h>
#include <linux/io.h>
#include <linux/kernel.h>
#include <linux/ktime.h>
#include <linux/hashtable.h>
#include <linux/list.h>
#include <linux/module.h>
#include <linux/of_address.h>
#include <linux/of_device.h>
#include <linux/processor.h>
#include <linux/refcount.h>
#include <linux/slab.h>

#include "common.h"
#include "notify.h"

#define CREATE_TRACE_POINTS
#include <trace/events/scmi.h>

enum scmi_error_codes {
        SCMI_SUCCESS = 0,       /* Success */
        SCMI_ERR_SUPPORT = -1,  /* Not supported */
        SCMI_ERR_PARAMS = -2,   /* Invalid Parameters */
        SCMI_ERR_ACCESS = -3,   /* Invalid access/permission denied */
        SCMI_ERR_ENTRY = -4,    /* Not found */
        SCMI_ERR_RANGE = -5,    /* Value out of range */
        SCMI_ERR_BUSY = -6,     /* Device busy */
        SCMI_ERR_COMMS = -7,    /* Communication Error */
        SCMI_ERR_GENERIC = -8,  /* Generic Error */
        SCMI_ERR_HARDWARE = -9, /* Hardware Error */
        SCMI_ERR_PROTOCOL = -10,/* Protocol Error */
};

/* List of all SCMI devices active in system */
static LIST_HEAD(scmi_list);
/* Protection for the entire list */
static DEFINE_MUTEX(scmi_list_mutex);
/* Track the unique id for the transfers for debug & profiling purpose */
static atomic_t transfer_last_id;

static DEFINE_IDR(scmi_requested_devices);
static DEFINE_MUTEX(scmi_requested_devices_mtx);

struct scmi_requested_dev {
        const struct scmi_device_id *id_table;
        struct list_head node;
};

/**
 * struct scmi_xfers_info - Structure to manage transfer information
 *
 * @xfer_alloc_table: Bitmap table for allocated messages.
 *      Index of this bitmap table is also used for message
 *      sequence identifier.
 * @xfer_lock: Protection for message allocation
 * @max_msg: Maximum number of messages that can be pending
 * @free_xfers: A free list for available to use xfers. It is initialized with
 *              a number of xfers equal to the maximum allowed in-flight
 *              messages.
 * @pending_xfers: An hashtable, indexed by msg_hdr.seq, used to keep all the
 *                 currently in-flight messages.
 */
struct scmi_xfers_info {
        unsigned long *xfer_alloc_table;
        spinlock_t xfer_lock;
        int max_msg;
        struct hlist_head free_xfers;
        DECLARE_HASHTABLE(pending_xfers, SCMI_PENDING_XFERS_HT_ORDER_SZ);
};

/**
 * struct scmi_protocol_instance  - Describe an initialized protocol instance.
 * @handle: Reference to the SCMI handle associated to this protocol instance.
 * @proto: A reference to the protocol descriptor.
 * @gid: A reference for per-protocol devres management.
 * @users: A refcount to track effective users of this protocol.
 * @priv: Reference for optional protocol private data.
 * @ph: An embedded protocol handle that will be passed down to protocol
 *      initialization code to identify this instance.
 *
 * Each protocol is initialized independently once for each SCMI platform in
 * which is defined by DT and implemented by the SCMI server fw.
 */
struct scmi_protocol_instance {
        const struct scmi_handle        *handle;
        const struct scmi_protocol      *proto;
        void                            *gid;
        refcount_t                      users;
        void                            *priv;
        struct scmi_protocol_handle     ph;
};

#define ph_to_pi(h)     container_of(h, struct scmi_protocol_instance, ph)

/**
 * struct scmi_info - Structure representing a SCMI instance
 *
 * @dev: Device pointer
 * @desc: SoC description for this instance
 * @version: SCMI revision information containing protocol version,
 *      implementation version and (sub-)vendor identification.
 * @handle: Instance of SCMI handle to send to clients
 * @tx_minfo: Universal Transmit Message management info
 * @rx_minfo: Universal Receive Message management info
 * @tx_idr: IDR object to map protocol id to Tx channel info pointer
 * @rx_idr: IDR object to map protocol id to Rx channel info pointer
 * @protocols: IDR for protocols' instance descriptors initialized for
 *             this SCMI instance: populated on protocol's first attempted
 *             usage.
 * @protocols_mtx: A mutex to protect protocols instances initialization.
 * @protocols_imp: List of protocols implemented, currently maximum of
 *      MAX_PROTOCOLS_IMP elements allocated by the base protocol
 * @active_protocols: IDR storing device_nodes for protocols actually defined
 *                    in the DT and confirmed as implemented by fw.
 * @notify_priv: Pointer to private data structure specific to notifications.
 * @node: List head
 * @users: Number of users of this instance
 */
struct scmi_info {
        struct device *dev;
        const struct scmi_desc *desc;
        struct scmi_revision_info version;
        struct scmi_handle handle;
        struct scmi_xfers_info tx_minfo;
        struct scmi_xfers_info rx_minfo;
        struct idr tx_idr;
        struct idr rx_idr;
        struct idr protocols;
        /* Ensure mutual exclusive access to protocols instance array */
        struct mutex protocols_mtx;
        u8 *protocols_imp;
        struct idr active_protocols;
        void *notify_priv;
        struct list_head node;
        int users;
};

#define handle_to_scmi_info(h)  container_of(h, struct scmi_info, handle)

static const int scmi_linux_errmap[] = {
        /* better than switch case as long as return value is continuous */
        0,                      /* SCMI_SUCCESS */
        -EOPNOTSUPP,            /* SCMI_ERR_SUPPORT */
        -EINVAL,                /* SCMI_ERR_PARAM */
        -EACCES,                /* SCMI_ERR_ACCESS */
        -ENOENT,                /* SCMI_ERR_ENTRY */
        -ERANGE,                /* SCMI_ERR_RANGE */
        -EBUSY,                 /* SCMI_ERR_BUSY */
        -ECOMM,                 /* SCMI_ERR_COMMS */
        -EIO,                   /* SCMI_ERR_GENERIC */
        -EREMOTEIO,             /* SCMI_ERR_HARDWARE */
        -EPROTO,                /* SCMI_ERR_PROTOCOL */
};

static inline int scmi_to_linux_errno(int errno)
{
        int err_idx = -errno;

        if (err_idx >= SCMI_SUCCESS && err_idx < ARRAY_SIZE(scmi_linux_errmap))
                return scmi_linux_errmap[err_idx];
        return -EIO;
}

void scmi_notification_instance_data_set(const struct scmi_handle *handle,
                                         void *priv)
{
        struct scmi_info *info = handle_to_scmi_info(handle);

        info->notify_priv = priv;
        /* Ensure updated protocol private date are visible */
        smp_wmb();
}

void *scmi_notification_instance_data_get(const struct scmi_handle *handle)
{
        struct scmi_info *info = handle_to_scmi_info(handle);

        /* Ensure protocols_private_data has been updated */
        smp_rmb();
        return info->notify_priv;
}

/**
 * scmi_xfer_token_set  - Reserve and set new token for the xfer at hand
 *
 * @minfo: Pointer to Tx/Rx Message management info based on channel type
 * @xfer: The xfer to act upon
 *
 * Pick the next unused monotonically increasing token and set it into
 * xfer->hdr.seq: picking a monotonically increasing value avoids immediate
 * reuse of freshly completed or timed-out xfers, thus mitigating the risk
 * of incorrect association of a late and expired xfer with a live in-flight
 * transaction, both happening to re-use the same token identifier.
 *
 * Since platform is NOT required to answer our request in-order we should
 * account for a few rare but possible scenarios:
 *
 *  - exactly 'next_token' may be NOT available so pick xfer_id >= next_token
 *    using find_next_zero_bit() starting from candidate next_token bit
 *
 *  - all tokens ahead upto (MSG_TOKEN_ID_MASK - 1) are used in-flight but we
 *    are plenty of free tokens at start, so try a second pass using
 *    find_next_zero_bit() and starting from 0.
 *
 *  X = used in-flight
 *
 * Normal
 * ------
 *
 *              |- xfer_id picked
 *   -----------+----------------------------------------------------------
 *   | | |X|X|X| | | | | | ... ... ... ... ... ... ... ... ... ... ...|X|X|
 *   ----------------------------------------------------------------------
 *              ^
 *              |- next_token
 *
 * Out-of-order pending at start
 * -----------------------------
 *
 *        |- xfer_id picked, last_token fixed
 *   -----+----------------------------------------------------------------
 *   |X|X| | | | |X|X| ... ... ... ... ... ... ... ... ... ... ... ...|X| |
 *   ----------------------------------------------------------------------
 *    ^
 *    |- next_token
 *
 *
 * Out-of-order pending at end
 * ---------------------------
 *
 *        |- xfer_id picked, last_token fixed
 *   -----+----------------------------------------------------------------
 *   |X|X| | | | |X|X| ... ... ... ... ... ... ... ... ... ... |X|X|X||X|X|
 *   ----------------------------------------------------------------------
 *                                                              ^
 *                                                              |- next_token
 *
 * Context: Assumes to be called with @xfer_lock already acquired.
 *
 * Return: 0 on Success or error
 */
static int scmi_xfer_token_set(struct scmi_xfers_info *minfo,
                               struct scmi_xfer *xfer)
{
        unsigned long xfer_id, next_token;

        /*
         * Pick a candidate monotonic token in range [0, MSG_TOKEN_MAX - 1]
         * using the pre-allocated transfer_id as a base.
         * Note that the global transfer_id is shared across all message types
         * so there could be holes in the allocated set of monotonic sequence
         * numbers, but that is going to limit the effectiveness of the
         * mitigation only in very rare limit conditions.
         */
        next_token = (xfer->transfer_id & (MSG_TOKEN_MAX - 1));

        /* Pick the next available xfer_id >= next_token */
        xfer_id = find_next_zero_bit(minfo->xfer_alloc_table,
                                     MSG_TOKEN_MAX, next_token);
        if (xfer_id == MSG_TOKEN_MAX) {
                /*
                 * After heavily out-of-order responses, there are no free
                 * tokens ahead, but only at start of xfer_alloc_table so
                 * try again from the beginning.
                 */
                xfer_id = find_next_zero_bit(minfo->xfer_alloc_table,
                                             MSG_TOKEN_MAX, 0);
                /*
                 * Something is wrong if we got here since there can be a
                 * maximum number of (MSG_TOKEN_MAX - 1) in-flight messages
                 * but we have not found any free token [0, MSG_TOKEN_MAX - 1].
                 */
                if (WARN_ON_ONCE(xfer_id == MSG_TOKEN_MAX))
                        return -ENOMEM;
        }

        /* Update +/- last_token accordingly if we skipped some hole */
        if (xfer_id != next_token)
                atomic_add((int)(xfer_id - next_token), &transfer_last_id);

        /* Set in-flight */
        set_bit(xfer_id, minfo->xfer_alloc_table);
        xfer->hdr.seq = (u16)xfer_id;

        return 0;
}

/**
 * scmi_xfer_token_clear  - Release the token
 *
 * @minfo: Pointer to Tx/Rx Message management info based on channel type
 * @xfer: The xfer to act upon
 */
static inline void scmi_xfer_token_clear(struct scmi_xfers_info *minfo,
                                         struct scmi_xfer *xfer)
{
        clear_bit(xfer->hdr.seq, minfo->xfer_alloc_table);
}

/**
 * scmi_xfer_get() - Allocate one message
 *
 * @handle: Pointer to SCMI entity handle
 * @minfo: Pointer to Tx/Rx Message management info based on channel type
 * @set_pending: If true a monotonic token is picked and the xfer is added to
 *               the pending hash table.
 *
 * Helper function which is used by various message functions that are
 * exposed to clients of this driver for allocating a message traffic event.
 *
 * Picks an xfer from the free list @free_xfers (if any available) and, if
 * required, sets a monotonically increasing token and stores the inflight xfer
 * into the @pending_xfers hashtable for later retrieval.
 *
 * The successfully initialized xfer is refcounted.
 *
 * Context: Holds @xfer_lock while manipulating @xfer_alloc_table and
 *          @free_xfers.
 *
 * Return: 0 if all went fine, else corresponding error.
 */
static struct scmi_xfer *scmi_xfer_get(const struct scmi_handle *handle,
                                       struct scmi_xfers_info *minfo,
                                       bool set_pending)
{
        int ret;
        unsigned long flags;
        struct scmi_xfer *xfer;

        spin_lock_irqsave(&minfo->xfer_lock, flags);
        if (hlist_empty(&minfo->free_xfers)) {
                spin_unlock_irqrestore(&minfo->xfer_lock, flags);
                return ERR_PTR(-ENOMEM);
        }

        /* grab an xfer from the free_list */
        xfer = hlist_entry(minfo->free_xfers.first, struct scmi_xfer, node);
        hlist_del_init(&xfer->node);

        /*
         * Allocate transfer_id early so that can be used also as base for
         * monotonic sequence number generation if needed.
         */
        xfer->transfer_id = atomic_inc_return(&transfer_last_id);

        if (set_pending) {
                /* Pick and set monotonic token */
                ret = scmi_xfer_token_set(minfo, xfer);
                if (!ret) {
                        hash_add(minfo->pending_xfers, &xfer->node,
                                 xfer->hdr.seq);
                        xfer->pending = true;
                } else {
                        dev_err(handle->dev,
                                "Failed to get monotonic token %d\n", ret);
                        hlist_add_head(&xfer->node, &minfo->free_xfers);
                        xfer = ERR_PTR(ret);
                }
        }

        if (!IS_ERR(xfer)) {
                refcount_set(&xfer->users, 1);
                atomic_set(&xfer->busy, SCMI_XFER_FREE);
        }
        spin_unlock_irqrestore(&minfo->xfer_lock, flags);

        return xfer;
}

/**
 * __scmi_xfer_put() - Release a message
 *
 * @minfo: Pointer to Tx/Rx Message management info based on channel type
 * @xfer: message that was reserved by scmi_xfer_get
 *
 * After refcount check, possibly release an xfer, clearing the token slot,
 * removing xfer from @pending_xfers and putting it back into free_xfers.
 *
 * This holds a spinlock to maintain integrity of internal data structures.
 */
static void
__scmi_xfer_put(struct scmi_xfers_info *minfo, struct scmi_xfer *xfer)
{
        unsigned long flags;

        spin_lock_irqsave(&minfo->xfer_lock, flags);
        if (refcount_dec_and_test(&xfer->users)) {
                if (xfer->pending) {
                        scmi_xfer_token_clear(minfo, xfer);
                        hash_del(&xfer->node);
                        xfer->pending = false;
                }
                hlist_add_head(&xfer->node, &minfo->free_xfers);
        }
        spin_unlock_irqrestore(&minfo->xfer_lock, flags);
}

/**
 * scmi_xfer_lookup_unlocked  -  Helper to lookup an xfer_id
 *
 * @minfo: Pointer to Tx/Rx Message management info based on channel type
 * @xfer_id: Token ID to lookup in @pending_xfers
 *
 * Refcounting is untouched.
 *
 * Context: Assumes to be called with @xfer_lock already acquired.
 *
 * Return: A valid xfer on Success or error otherwise
 */
static struct scmi_xfer *
scmi_xfer_lookup_unlocked(struct scmi_xfers_info *minfo, u16 xfer_id)
{
        struct scmi_xfer *xfer = NULL;

        if (test_bit(xfer_id, minfo->xfer_alloc_table))
                xfer = XFER_FIND(minfo->pending_xfers, xfer_id);

        return xfer ?: ERR_PTR(-EINVAL);
}

/**
 * scmi_msg_response_validate  - Validate message type against state of related
 * xfer
 *
 * @cinfo: A reference to the channel descriptor.
 * @msg_type: Message type to check
 * @xfer: A reference to the xfer to validate against @msg_type
 *
 * This function checks if @msg_type is congruent with the current state of
 * a pending @xfer; if an asynchronous delayed response is received before the
 * related synchronous response (Out-of-Order Delayed Response) the missing
 * synchronous response is assumed to be OK and completed, carrying on with the
 * Delayed Response: this is done to address the case in which the underlying
 * SCMI transport can deliver such out-of-order responses.
 *
 * Context: Assumes to be called with xfer->lock already acquired.
 *
 * Return: 0 on Success, error otherwise
 */
static inline int scmi_msg_response_validate(struct scmi_chan_info *cinfo,
                                             u8 msg_type,
                                             struct scmi_xfer *xfer)
{
        /*
         * Even if a response was indeed expected on this slot at this point,
         * a buggy platform could wrongly reply feeding us an unexpected
         * delayed response we're not prepared to handle: bail-out safely
         * blaming firmware.
         */
        if (msg_type == MSG_TYPE_DELAYED_RESP && !xfer->async_done) {
                dev_err(cinfo->dev,
                        "Delayed Response for %d not expected! Buggy F/W ?\n",
                        xfer->hdr.seq);
                return -EINVAL;
        }

        switch (xfer->state) {
        case SCMI_XFER_SENT_OK:
                if (msg_type == MSG_TYPE_DELAYED_RESP) {
                        /*
                         * Delayed Response expected but delivered earlier.
                         * Assume message RESPONSE was OK and skip state.
                         */
                        xfer->hdr.status = SCMI_SUCCESS;
                        xfer->state = SCMI_XFER_RESP_OK;
                        complete(&xfer->done);
                        dev_warn(cinfo->dev,
                                 "Received valid OoO Delayed Response for %d\n",
                                 xfer->hdr.seq);
                }
                break;
        case SCMI_XFER_RESP_OK:
                if (msg_type != MSG_TYPE_DELAYED_RESP)
                        return -EINVAL;
                break;
        case SCMI_XFER_DRESP_OK:
                /* No further message expected once in SCMI_XFER_DRESP_OK */
                return -EINVAL;
        }

        return 0;
}

/**
 * scmi_xfer_state_update  - Update xfer state
 *
 * @xfer: A reference to the xfer to update
 * @msg_type: Type of message being processed.
 *
 * Note that this message is assumed to have been already successfully validated
 * by @scmi_msg_response_validate(), so here we just update the state.
 *
 * Context: Assumes to be called on an xfer exclusively acquired using the
 *          busy flag.
 */
static inline void scmi_xfer_state_update(struct scmi_xfer *xfer, u8 msg_type)
{
        xfer->hdr.type = msg_type;

        /* Unknown command types were already discarded earlier */
        if (xfer->hdr.type == MSG_TYPE_COMMAND)
                xfer->state = SCMI_XFER_RESP_OK;
        else
                xfer->state = SCMI_XFER_DRESP_OK;
}

static bool scmi_xfer_acquired(struct scmi_xfer *xfer)
{
        int ret;

        ret = atomic_cmpxchg(&xfer->busy, SCMI_XFER_FREE, SCMI_XFER_BUSY);

        return ret == SCMI_XFER_FREE;
}

/**
 * scmi_xfer_command_acquire  -  Helper to lookup and acquire a command xfer
 *
 * @cinfo: A reference to the channel descriptor.
 * @msg_hdr: A message header to use as lookup key
 *
 * When a valid xfer is found for the sequence number embedded in the provided
 * msg_hdr, reference counting is properly updated and exclusive access to this
 * xfer is granted till released with @scmi_xfer_command_release.
 *
 * Return: A valid @xfer on Success or error otherwise.
 */
static inline struct scmi_xfer *
scmi_xfer_command_acquire(struct scmi_chan_info *cinfo, u32 msg_hdr)
{
        int ret;
        unsigned long flags;
        struct scmi_xfer *xfer;
        struct scmi_info *info = handle_to_scmi_info(cinfo->handle);
        struct scmi_xfers_info *minfo = &info->tx_minfo;
        u8 msg_type = MSG_XTRACT_TYPE(msg_hdr);
        u16 xfer_id = MSG_XTRACT_TOKEN(msg_hdr);

        /* Are we even expecting this? */
        spin_lock_irqsave(&minfo->xfer_lock, flags);
        xfer = scmi_xfer_lookup_unlocked(minfo, xfer_id);
        if (IS_ERR(xfer)) {
                dev_err(cinfo->dev,
                        "Message for %d type %d is not expected!\n",
                        xfer_id, msg_type);
                spin_unlock_irqrestore(&minfo->xfer_lock, flags);
                return xfer;
        }
        refcount_inc(&xfer->users);
        spin_unlock_irqrestore(&minfo->xfer_lock, flags);

        spin_lock_irqsave(&xfer->lock, flags);
        ret = scmi_msg_response_validate(cinfo, msg_type, xfer);
        /*
         * If a pending xfer was found which was also in a congruent state with
         * the received message, acquire exclusive access to it setting the busy
         * flag.
         * Spins only on the rare limit condition of concurrent reception of
         * RESP and DRESP for the same xfer.
         */
        if (!ret) {
                spin_until_cond(scmi_xfer_acquired(xfer));
                scmi_xfer_state_update(xfer, msg_type);
        }
        spin_unlock_irqrestore(&xfer->lock, flags);

        if (ret) {
                dev_err(cinfo->dev,
                        "Invalid message type:%d for %d - HDR:0x%X  state:%d\n",
                        msg_type, xfer_id, msg_hdr, xfer->state);
                /* On error the refcount incremented above has to be dropped */
                __scmi_xfer_put(minfo, xfer);
                xfer = ERR_PTR(-EINVAL);
        }

        return xfer;
}

static inline void scmi_xfer_command_release(struct scmi_info *info,
                                             struct scmi_xfer *xfer)
{
        atomic_set(&xfer->busy, SCMI_XFER_FREE);
        __scmi_xfer_put(&info->tx_minfo, xfer);
}

static inline void scmi_clear_channel(struct scmi_info *info,
                                      struct scmi_chan_info *cinfo)
{
        if (info->desc->ops->clear_channel)
                info->desc->ops->clear_channel(cinfo);
}

static void scmi_handle_notification(struct scmi_chan_info *cinfo,
                                     u32 msg_hdr, void *priv)
{
        struct scmi_xfer *xfer;
        struct device *dev = cinfo->dev;
        struct scmi_info *info = handle_to_scmi_info(cinfo->handle);
        struct scmi_xfers_info *minfo = &info->rx_minfo;
        ktime_t ts;

        ts = ktime_get_boottime();
        xfer = scmi_xfer_get(cinfo->handle, minfo, false);
        if (IS_ERR(xfer)) {
                dev_err(dev, "failed to get free message slot (%ld)\n",
                        PTR_ERR(xfer));
                scmi_clear_channel(info, cinfo);
                return;
        }

        unpack_scmi_header(msg_hdr, &xfer->hdr);
        if (priv)
                xfer->priv = priv;
        info->desc->ops->fetch_notification(cinfo, info->desc->max_msg_size,
                                            xfer);
        scmi_notify(cinfo->handle, xfer->hdr.protocol_id,
                    xfer->hdr.id, xfer->rx.buf, xfer->rx.len, ts);

        trace_scmi_rx_done(xfer->transfer_id, xfer->hdr.id,
                           xfer->hdr.protocol_id, xfer->hdr.seq,
                           MSG_TYPE_NOTIFICATION);

        __scmi_xfer_put(minfo, xfer);

        scmi_clear_channel(info, cinfo);
}

static void scmi_handle_response(struct scmi_chan_info *cinfo,
                                 u32 msg_hdr, void *priv)
{
        struct scmi_xfer *xfer;
        struct scmi_info *info = handle_to_scmi_info(cinfo->handle);

        xfer = scmi_xfer_command_acquire(cinfo, msg_hdr);
        if (IS_ERR(xfer)) {
                if (MSG_XTRACT_TYPE(msg_hdr) == MSG_TYPE_DELAYED_RESP)
                        scmi_clear_channel(info, cinfo);
                return;
        }

        /* rx.len could be shrunk in the sync do_xfer, so reset to maxsz */
        if (xfer->hdr.type == MSG_TYPE_DELAYED_RESP)
                xfer->rx.len = info->desc->max_msg_size;

        if (priv)
                xfer->priv = priv;
        info->desc->ops->fetch_response(cinfo, xfer);

        trace_scmi_rx_done(xfer->transfer_id, xfer->hdr.id,
                           xfer->hdr.protocol_id, xfer->hdr.seq,
                           xfer->hdr.type);

        if (xfer->hdr.type == MSG_TYPE_DELAYED_RESP) {
                scmi_clear_channel(info, cinfo);
                complete(xfer->async_done);
        } else {
                complete(&xfer->done);
        }

        scmi_xfer_command_release(info, xfer);
}

/**
 * scmi_rx_callback() - callback for receiving messages
 *
 * @cinfo: SCMI channel info
 * @msg_hdr: Message header
 * @priv: Transport specific private data.
 *
 * Processes one received message to appropriate transfer information and
 * signals completion of the transfer.
 *
 * NOTE: This function will be invoked in IRQ context, hence should be
 * as optimal as possible.
 */
void scmi_rx_callback(struct scmi_chan_info *cinfo, u32 msg_hdr, void *priv)
{
        u8 msg_type = MSG_XTRACT_TYPE(msg_hdr);

        switch (msg_type) {
        case MSG_TYPE_NOTIFICATION:
                scmi_handle_notification(cinfo, msg_hdr, priv);
                break;
        case MSG_TYPE_COMMAND:
        case MSG_TYPE_DELAYED_RESP:
                scmi_handle_response(cinfo, msg_hdr, priv);
                break;
        default:
                WARN_ONCE(1, "received unknown msg_type:%d\n", msg_type);
                break;
        }
}

/**
 * xfer_put() - Release a transmit message
 *
 * @ph: Pointer to SCMI protocol handle
 * @xfer: message that was reserved by xfer_get_init
 */
static void xfer_put(const struct scmi_protocol_handle *ph,
                     struct scmi_xfer *xfer)
{
        const struct scmi_protocol_instance *pi = ph_to_pi(ph);
        struct scmi_info *info = handle_to_scmi_info(pi->handle);

        __scmi_xfer_put(&info->tx_minfo, xfer);
}

#define SCMI_MAX_POLL_TO_NS     (100 * NSEC_PER_USEC)

static bool scmi_xfer_done_no_timeout(struct scmi_chan_info *cinfo,
                                      struct scmi_xfer *xfer, ktime_t stop)
{
        struct scmi_info *info = handle_to_scmi_info(cinfo->handle);

        /*
         * Poll also on xfer->done so that polling can be forcibly terminated
         * in case of out-of-order receptions of delayed responses
         */
        return info->desc->ops->poll_done(cinfo, xfer) ||
               try_wait_for_completion(&xfer->done) ||
               ktime_after(ktime_get(), stop);
}

/**
 * do_xfer() - Do one transfer
 *
 * @ph: Pointer to SCMI protocol handle
 * @xfer: Transfer to initiate and wait for response
 *
 * Return: -ETIMEDOUT in case of no response, if transmit error,
 *      return corresponding error, else if all goes well,
 *      return 0.
 */
static int do_xfer(const struct scmi_protocol_handle *ph,
                   struct scmi_xfer *xfer)
{
        int ret;
        int timeout;
        const struct scmi_protocol_instance *pi = ph_to_pi(ph);
        struct scmi_info *info = handle_to_scmi_info(pi->handle);
        struct device *dev = info->dev;
        struct scmi_chan_info *cinfo;

        if (xfer->hdr.poll_completion && !info->desc->ops->poll_done) {
                dev_warn_once(dev,
                              "Polling mode is not supported by transport.\n");
                return -EINVAL;
        }

        /*
         * Initialise protocol id now from protocol handle to avoid it being
         * overridden by mistake (or malice) by the protocol code mangling with
         * the scmi_xfer structure prior to this.
         */
        xfer->hdr.protocol_id = pi->proto->id;
        reinit_completion(&xfer->done);

        cinfo = idr_find(&info->tx_idr, xfer->hdr.protocol_id);
        if (unlikely(!cinfo))
                return -EINVAL;

        trace_scmi_xfer_begin(xfer->transfer_id, xfer->hdr.id,
                              xfer->hdr.protocol_id, xfer->hdr.seq,
                              xfer->hdr.poll_completion);

        /* Clear any stale status */
        xfer->hdr.status = SCMI_SUCCESS;
        xfer->state = SCMI_XFER_SENT_OK;
        /*
         * Even though spinlocking is not needed here since no race is possible
         * on xfer->state due to the monotonically increasing tokens allocation,
         * we must anyway ensure xfer->state initialization is not re-ordered
         * after the .send_message() to be sure that on the RX path an early
         * ISR calling scmi_rx_callback() cannot see an old stale xfer->state.
         */
        smp_mb();

        ret = info->desc->ops->send_message(cinfo, xfer);
        if (ret < 0) {
                dev_dbg(dev, "Failed to send message %d\n", ret);
                return ret;
        }

        if (xfer->hdr.poll_completion) {
                ktime_t stop = ktime_add_ns(ktime_get(), SCMI_MAX_POLL_TO_NS);

                spin_until_cond(scmi_xfer_done_no_timeout(cinfo, xfer, stop));
                if (ktime_before(ktime_get(), stop)) {
                        unsigned long flags;

                        /*
                         * Do not fetch_response if an out-of-order delayed
                         * response is being processed.
                         */
                        spin_lock_irqsave(&xfer->lock, flags);
                        if (xfer->state == SCMI_XFER_SENT_OK) {
                                info->desc->ops->fetch_response(cinfo, xfer);
                                xfer->state = SCMI_XFER_RESP_OK;
                        }
                        spin_unlock_irqrestore(&xfer->lock, flags);
                } else {
                        ret = -ETIMEDOUT;
                }
        } else {
                /* And we wait for the response. */
                timeout = msecs_to_jiffies(info->desc->max_rx_timeout_ms);
                if (!wait_for_completion_timeout(&xfer->done, timeout)) {
                        dev_err(dev, "timed out in resp(caller: %pS)\n",
                                (void *)_RET_IP_);
                        ret = -ETIMEDOUT;
                }
        }

        if (!ret && xfer->hdr.status)
                ret = scmi_to_linux_errno(xfer->hdr.status);

        if (info->desc->ops->mark_txdone)
                info->desc->ops->mark_txdone(cinfo, ret);

        trace_scmi_xfer_end(xfer->transfer_id, xfer->hdr.id,
                            xfer->hdr.protocol_id, xfer->hdr.seq, ret);

        return ret;
}

static void reset_rx_to_maxsz(const struct scmi_protocol_handle *ph,
                              struct scmi_xfer *xfer)
{
        const struct scmi_protocol_instance *pi = ph_to_pi(ph);
        struct scmi_info *info = handle_to_scmi_info(pi->handle);

        xfer->rx.len = info->desc->max_msg_size;
}

#define SCMI_MAX_RESPONSE_TIMEOUT       (2 * MSEC_PER_SEC)

/**
 * do_xfer_with_response() - Do one transfer and wait until the delayed
 *      response is received
 *
 * @ph: Pointer to SCMI protocol handle
 * @xfer: Transfer to initiate and wait for response
 *
 * Return: -ETIMEDOUT in case of no delayed response, if transmit error,
 *      return corresponding error, else if all goes well, return 0.
 */
static int do_xfer_with_response(const struct scmi_protocol_handle *ph,
                                 struct scmi_xfer *xfer)
{
        int ret, timeout = msecs_to_jiffies(SCMI_MAX_RESPONSE_TIMEOUT);
        DECLARE_COMPLETION_ONSTACK(async_response);

        xfer->async_done = &async_response;

        ret = do_xfer(ph, xfer);
        if (!ret) {
                if (!wait_for_completion_timeout(xfer->async_done, timeout))
                        ret = -ETIMEDOUT;
                else if (xfer->hdr.status)
                        ret = scmi_to_linux_errno(xfer->hdr.status);
        }

        xfer->async_done = NULL;
        return ret;
}

/**
 * xfer_get_init() - Allocate and initialise one message for transmit
 *
 * @ph: Pointer to SCMI protocol handle
 * @msg_id: Message identifier
 * @tx_size: transmit message size
 * @rx_size: receive message size
 * @p: pointer to the allocated and initialised message
 *
 * This function allocates the message using @scmi_xfer_get and
 * initialise the header.
 *
 * Return: 0 if all went fine with @p pointing to message, else
 *      corresponding error.
 */
static int xfer_get_init(const struct scmi_protocol_handle *ph,
                         u8 msg_id, size_t tx_size, size_t rx_size,
                         struct scmi_xfer **p)
{
        int ret;
        struct scmi_xfer *xfer;
        const struct scmi_protocol_instance *pi = ph_to_pi(ph);
        struct scmi_info *info = handle_to_scmi_info(pi->handle);
        struct scmi_xfers_info *minfo = &info->tx_minfo;
        struct device *dev = info->dev;

        /* Ensure we have sane transfer sizes */
        if (rx_size > info->desc->max_msg_size ||
            tx_size > info->desc->max_msg_size)
                return -ERANGE;

        xfer = scmi_xfer_get(pi->handle, minfo, true);
        if (IS_ERR(xfer)) {
                ret = PTR_ERR(xfer);
                dev_err(dev, "failed to get free message slot(%d)\n", ret);
                return ret;
        }

        xfer->tx.len = tx_size;
        xfer->rx.len = rx_size ? : info->desc->max_msg_size;
        xfer->hdr.type = MSG_TYPE_COMMAND;
        xfer->hdr.id = msg_id;
        xfer->hdr.poll_completion = false;

        *p = xfer;

        return 0;
}

/**
 * version_get() - command to get the revision of the SCMI entity
 *
 * @ph: Pointer to SCMI protocol handle
 * @version: Holds returned version of protocol.
 *
 * Updates the SCMI information in the internal data structure.
 *
 * Return: 0 if all went fine, else return appropriate error.
 */
static int version_get(const struct scmi_protocol_handle *ph, u32 *version)
{
        int ret;
        __le32 *rev_info;
        struct scmi_xfer *t;

        ret = xfer_get_init(ph, PROTOCOL_VERSION, 0, sizeof(*version), &t);
        if (ret)
                return ret;

        ret = do_xfer(ph, t);
        if (!ret) {
                rev_info = t->rx.buf;
                *version = le32_to_cpu(*rev_info);
        }

        xfer_put(ph, t);
        return ret;
}

/**
 * scmi_set_protocol_priv  - Set protocol specific data at init time
 *
 * @ph: A reference to the protocol handle.
 * @priv: The private data to set.
 *
 * Return: 0 on Success
 */
static int scmi_set_protocol_priv(const struct scmi_protocol_handle *ph,
                                  void *priv)
{
        struct scmi_protocol_instance *pi = ph_to_pi(ph);

        pi->priv = priv;

        return 0;
}

/**
 * scmi_get_protocol_priv  - Set protocol specific data at init time
 *
 * @ph: A reference to the protocol handle.
 *
 * Return: Protocol private data if any was set.
 */
static void *scmi_get_protocol_priv(const struct scmi_protocol_handle *ph)
{
        const struct scmi_protocol_instance *pi = ph_to_pi(ph);

        return pi->priv;
}

static const struct scmi_xfer_ops xfer_ops = {
        .version_get = version_get,
        .xfer_get_init = xfer_get_init,
        .reset_rx_to_maxsz = reset_rx_to_maxsz,
        .do_xfer = do_xfer,
        .do_xfer_with_response = do_xfer_with_response,
        .xfer_put = xfer_put,
};

/**
 * scmi_revision_area_get  - Retrieve version memory area.
 *
 * @ph: A reference to the protocol handle.
 *
 * A helper to grab the version memory area reference during SCMI Base protocol
 * initialization.
 *
 * Return: A reference to the version memory area associated to the SCMI
 *         instance underlying this protocol handle.
 */
struct scmi_revision_info *
scmi_revision_area_get(const struct scmi_protocol_handle *ph)
{
        const struct scmi_protocol_instance *pi = ph_to_pi(ph);

        return pi->handle->version;
}

/**
 * scmi_alloc_init_protocol_instance  - Allocate and initialize a protocol
 * instance descriptor.
 * @info: The reference to the related SCMI instance.
 * @proto: The protocol descriptor.
 *
 * Allocate a new protocol instance descriptor, using the provided @proto
 * description, against the specified SCMI instance @info, and initialize it;
 * all resources management is handled via a dedicated per-protocol devres
 * group.
 *
 * Context: Assumes to be called with @protocols_mtx already acquired.
 * Return: A reference to a freshly allocated and initialized protocol instance
 *         or ERR_PTR on failure. On failure the @proto reference is at first
 *         put using @scmi_protocol_put() before releasing all the devres group.
 */
static struct scmi_protocol_instance *
scmi_alloc_init_protocol_instance(struct scmi_info *info,
                                  const struct scmi_protocol *proto)
{
        int ret = -ENOMEM;
        void *gid;
        struct scmi_protocol_instance *pi;
        const struct scmi_handle *handle = &info->handle;

        /* Protocol specific devres group */
        gid = devres_open_group(handle->dev, NULL, GFP_KERNEL);
        if (!gid) {
                scmi_protocol_put(proto->id);
                goto out;
        }

        pi = devm_kzalloc(handle->dev, sizeof(*pi), GFP_KERNEL);
        if (!pi)
                goto clean;

        pi->gid = gid;
        pi->proto = proto;
        pi->handle = handle;
        pi->ph.dev = handle->dev;
        pi->ph.xops = &xfer_ops;
        pi->ph.set_priv = scmi_set_protocol_priv;
        pi->ph.get_priv = scmi_get_protocol_priv;
        refcount_set(&pi->users, 1);
        /* proto->init is assured NON NULL by scmi_protocol_register */
        ret = pi->proto->instance_init(&pi->ph);
        if (ret)
                goto clean;

        ret = idr_alloc(&info->protocols, pi, proto->id, proto->id + 1,
                        GFP_KERNEL);
        if (ret != proto->id)
                goto clean;

        /*
         * Warn but ignore events registration errors since we do not want
         * to skip whole protocols if their notifications are messed up.
         */
        if (pi->proto->events) {
                ret = scmi_register_protocol_events(handle, pi->proto->id,
                                                    &pi->ph,
                                                    pi->proto->events);
                if (ret)
                        dev_warn(handle->dev,
                                 "Protocol:%X - Events Registration Failed - err:%d\n",
                                 pi->proto->id, ret);
        }

        devres_close_group(handle->dev, pi->gid);
        dev_dbg(handle->dev, "Initialized protocol: 0x%X\n", pi->proto->id);

        return pi;

clean:
        /* Take care to put the protocol module's owner before releasing all */
        scmi_protocol_put(proto->id);
        devres_release_group(handle->dev, gid);
out:
        return ERR_PTR(ret);
}

/**
 * scmi_get_protocol_instance  - Protocol initialization helper.
 * @handle: A reference to the SCMI platform instance.
 * @protocol_id: The protocol being requested.
 *
 * In case the required protocol has never been requested before for this
 * instance, allocate and initialize all the needed structures while handling
 * resource allocation with a dedicated per-protocol devres subgroup.
 *
 * Return: A reference to an initialized protocol instance or error on failure:
 *         in particular returns -EPROBE_DEFER when the desired protocol could
 *         NOT be found.
 */
static struct scmi_protocol_instance * __must_check
scmi_get_protocol_instance(const struct scmi_handle *handle, u8 protocol_id)
{
        struct scmi_protocol_instance *pi;
        struct scmi_info *info = handle_to_scmi_info(handle);

        mutex_lock(&info->protocols_mtx);
        pi = idr_find(&info->protocols, protocol_id);

        if (pi) {
                refcount_inc(&pi->users);
        } else {
                const struct scmi_protocol *proto;

                /* Fails if protocol not registered on bus */
                proto = scmi_protocol_get(protocol_id);
                if (proto)
                        pi = scmi_alloc_init_protocol_instance(info, proto);
                else
                        pi = ERR_PTR(-EPROBE_DEFER);
        }
        mutex_unlock(&info->protocols_mtx);

        return pi;
}

/**
 * scmi_protocol_acquire  - Protocol acquire
 * @handle: A reference to the SCMI platform instance.
 * @protocol_id: The protocol being requested.
 *
 * Register a new user for the requested protocol on the specified SCMI
 * platform instance, possibly triggering its initialization on first user.
 *
 * Return: 0 if protocol was acquired successfully.
 */
int scmi_protocol_acquire(const struct scmi_handle *handle, u8 protocol_id)
{
        return PTR_ERR_OR_ZERO(scmi_get_protocol_instance(handle, protocol_id));
}

/**
 * scmi_protocol_release  - Protocol de-initialization helper.
 * @handle: A reference to the SCMI platform instance.
 * @protocol_id: The protocol being requested.
 *
 * Remove one user for the specified protocol and triggers de-initialization
 * and resources de-allocation once the last user has gone.
 */
void scmi_protocol_release(const struct scmi_handle *handle, u8 protocol_id)
{
        struct scmi_info *info = handle_to_scmi_info(handle);
        struct scmi_protocol_instance *pi;

        mutex_lock(&info->protocols_mtx);
        pi = idr_find(&info->protocols, protocol_id);
        if (WARN_ON(!pi))
                goto out;

        if (refcount_dec_and_test(&pi->users)) {
                void *gid = pi->gid;

                if (pi->proto->events)
                        scmi_deregister_protocol_events(handle, protocol_id);

                if (pi->proto->instance_deinit)
                        pi->proto->instance_deinit(&pi->ph);

                idr_remove(&info->protocols, protocol_id);

                scmi_protocol_put(protocol_id);

                devres_release_group(handle->dev, gid);
                dev_dbg(handle->dev, "De-Initialized protocol: 0x%X\n",
                        protocol_id);
        }

out:
        mutex_unlock(&info->protocols_mtx);
}

void scmi_setup_protocol_implemented(const struct scmi_protocol_handle *ph,
                                     u8 *prot_imp)
{
        const struct scmi_protocol_instance *pi = ph_to_pi(ph);
        struct scmi_info *info = handle_to_scmi_info(pi->handle);

        info->protocols_imp = prot_imp;
}

static bool
scmi_is_protocol_implemented(const struct scmi_handle *handle, u8 prot_id)
{
        int i;
        struct scmi_info *info = handle_to_scmi_info(handle);

        if (!info->protocols_imp)
                return false;

        for (i = 0; i < MAX_PROTOCOLS_IMP; i++)
                if (info->protocols_imp[i] == prot_id)
                        return true;
        return false;
}

struct scmi_protocol_devres {
        const struct scmi_handle *handle;
        u8 protocol_id;
};

static void scmi_devm_release_protocol(struct device *dev, void *res)
{
        struct scmi_protocol_devres *dres = res;

        scmi_protocol_release(dres->handle, dres->protocol_id);
}

/**
 * scmi_devm_protocol_get  - Devres managed get protocol operations and handle
 * @sdev: A reference to an scmi_device whose embedded struct device is to
 *        be used for devres accounting.
 * @protocol_id: The protocol being requested.
 * @ph: A pointer reference used to pass back the associated protocol handle.
 *
 * Get hold of a protocol accounting for its usage, eventually triggering its
 * initialization, and returning the protocol specific operations and related
 * protocol handle which will be used as first argument in most of the
 * protocols operations methods.
 * Being a devres based managed method, protocol hold will be automatically
 * released, and possibly de-initialized on last user, once the SCMI driver
 * owning the scmi_device is unbound from it.
 *
 * Return: A reference to the requested protocol operations or error.
 *         Must be checked for errors by caller.
 */
static const void __must_check *
scmi_devm_protocol_get(struct scmi_device *sdev, u8 protocol_id,
                       struct scmi_protocol_handle **ph)
{
        struct scmi_protocol_instance *pi;
        struct scmi_protocol_devres *dres;
        struct scmi_handle *handle = sdev->handle;

        if (!ph)
                return ERR_PTR(-EINVAL);

        dres = devres_alloc(scmi_devm_release_protocol,
                            sizeof(*dres), GFP_KERNEL);
        if (!dres)
                return ERR_PTR(-ENOMEM);

        pi = scmi_get_protocol_instance(handle, protocol_id);
        if (IS_ERR(pi)) {
                devres_free(dres);
                return pi;
        }

        dres->handle = handle;
        dres->protocol_id = protocol_id;
        devres_add(&sdev->dev, dres);

        *ph = &pi->ph;

        return pi->proto->ops;
}

static int scmi_devm_protocol_match(struct device *dev, void *res, void *data)
{
        struct scmi_protocol_devres *dres = res;

        if (WARN_ON(!dres || !data))
                return 0;

        return dres->protocol_id == *((u8 *)data);
}

/**
 * scmi_devm_protocol_put  - Devres managed put protocol operations and handle
 * @sdev: A reference to an scmi_device whose embedded struct device is to
 *        be used for devres accounting.
 * @protocol_id: The protocol being requested.
 *
 * Explicitly release a protocol hold previously obtained calling the above
 * @scmi_devm_protocol_get.
 */
static void scmi_devm_protocol_put(struct scmi_device *sdev, u8 protocol_id)
{
        int ret;

        ret = devres_release(&sdev->dev, scmi_devm_release_protocol,
                             scmi_devm_protocol_match, &protocol_id);
        WARN_ON(ret);
}

static inline
struct scmi_handle *scmi_handle_get_from_info_unlocked(struct scmi_info *info)
{
        info->users++;
        return &info->handle;
}

/**
 * scmi_handle_get() - Get the SCMI handle for a device
 *
 * @dev: pointer to device for which we want SCMI handle
 *
 * NOTE: The function does not track individual clients of the framework
 * and is expected to be maintained by caller of SCMI protocol library.
 * scmi_handle_put must be balanced with successful scmi_handle_get
 *
 * Return: pointer to handle if successful, NULL on error
 */
struct scmi_handle *scmi_handle_get(struct device *dev)
{
        struct list_head *p;
        struct scmi_info *info;
        struct scmi_handle *handle = NULL;

        mutex_lock(&scmi_list_mutex);
        list_for_each(p, &scmi_list) {
                info = list_entry(p, struct scmi_info, node);
                if (dev->parent == info->dev) {
                        handle = scmi_handle_get_from_info_unlocked(info);
                        break;
                }
        }
        mutex_unlock(&scmi_list_mutex);

        return handle;
}

/**
 * scmi_handle_put() - Release the handle acquired by scmi_handle_get
 *
 * @handle: handle acquired by scmi_handle_get
 *
 * NOTE: The function does not track individual clients of the framework
 * and is expected to be maintained by caller of SCMI protocol library.
 * scmi_handle_put must be balanced with successful scmi_handle_get
 *
 * Return: 0 is successfully released
 *      if null was passed, it returns -EINVAL;
 */
int scmi_handle_put(const struct scmi_handle *handle)
{
        struct scmi_info *info;

        if (!handle)
                return -EINVAL;

        info = handle_to_scmi_info(handle);
        mutex_lock(&scmi_list_mutex);
        if (!WARN_ON(!info->users))
                info->users--;
        mutex_unlock(&scmi_list_mutex);

        return 0;
}

static int __scmi_xfer_info_init(struct scmi_info *sinfo,
                                 struct scmi_xfers_info *info)
{
        int i;
        struct scmi_xfer *xfer;
        struct device *dev = sinfo->dev;
        const struct scmi_desc *desc = sinfo->desc;

        /* Pre-allocated messages, no more than what hdr.seq can support */
        if (WARN_ON(!info->max_msg || info->max_msg > MSG_TOKEN_MAX)) {
                dev_err(dev,
                        "Invalid maximum messages %d, not in range [1 - %lu]\n",
                        info->max_msg, MSG_TOKEN_MAX);
                return -EINVAL;
        }

        hash_init(info->pending_xfers);

        /* Allocate a bitmask sized to hold MSG_TOKEN_MAX tokens */
        info->xfer_alloc_table = devm_kcalloc(dev, BITS_TO_LONGS(MSG_TOKEN_MAX),
                                              sizeof(long), GFP_KERNEL);
        if (!info->xfer_alloc_table)
                return -ENOMEM;

        /*
         * Preallocate a number of xfers equal to max inflight messages,
         * pre-initialize the buffer pointer to pre-allocated buffers and
         * attach all of them to the free list
         */
        INIT_HLIST_HEAD(&info->free_xfers);
        for (i = 0; i < info->max_msg; i++) {
                xfer = devm_kzalloc(dev, sizeof(*xfer), GFP_KERNEL);
                if (!xfer)
                        return -ENOMEM;

                xfer->rx.buf = devm_kcalloc(dev, sizeof(u8), desc->max_msg_size,
                                            GFP_KERNEL);
                if (!xfer->rx.buf)
                        return -ENOMEM;

                xfer->tx.buf = xfer->rx.buf;
                init_completion(&xfer->done);
                spin_lock_init(&xfer->lock);

                /* Add initialized xfer to the free list */
                hlist_add_head(&xfer->node, &info->free_xfers);
        }

        spin_lock_init(&info->xfer_lock);

        return 0;
}

static int scmi_channels_max_msg_configure(struct scmi_info *sinfo)
{
        const struct scmi_desc *desc = sinfo->desc;

        if (!desc->ops->get_max_msg) {
                sinfo->tx_minfo.max_msg = desc->max_msg;
                sinfo->rx_minfo.max_msg = desc->max_msg;
        } else {
                struct scmi_chan_info *base_cinfo;

                base_cinfo = idr_find(&sinfo->tx_idr, SCMI_PROTOCOL_BASE);
                if (!base_cinfo)
                        return -EINVAL;
                sinfo->tx_minfo.max_msg = desc->ops->get_max_msg(base_cinfo);

                /* RX channel is optional so can be skipped */
                base_cinfo = idr_find(&sinfo->rx_idr, SCMI_PROTOCOL_BASE);
                if (base_cinfo)
                        sinfo->rx_minfo.max_msg =
                                desc->ops->get_max_msg(base_cinfo);
        }

        return 0;
}

static int scmi_xfer_info_init(struct scmi_info *sinfo)
{
        int ret;

        ret = scmi_channels_max_msg_configure(sinfo);
        if (ret)
                return ret;

        ret = __scmi_xfer_info_init(sinfo, &sinfo->tx_minfo);
        if (!ret && idr_find(&sinfo->rx_idr, SCMI_PROTOCOL_BASE))
                ret = __scmi_xfer_info_init(sinfo, &sinfo->rx_minfo);

        return ret;
}

static int scmi_chan_setup(struct scmi_info *info, struct device *dev,
                           int prot_id, bool tx)
{
        int ret, idx;
        struct scmi_chan_info *cinfo;
        struct idr *idr;

        /* Transmit channel is first entry i.e. index 0 */
        idx = tx ? 0 : 1;
        idr = tx ? &info->tx_idr : &info->rx_idr;

        /* check if already allocated, used for multiple device per protocol */
        cinfo = idr_find(idr, prot_id);
        if (cinfo)
                return 0;

        if (!info->desc->ops->chan_available(dev, idx)) {
                cinfo = idr_find(idr, SCMI_PROTOCOL_BASE);
                if (unlikely(!cinfo)) /* Possible only if platform has no Rx */
                        return -EINVAL;
                goto idr_alloc;
        }

        cinfo = devm_kzalloc(info->dev, sizeof(*cinfo), GFP_KERNEL);
        if (!cinfo)
                return -ENOMEM;

        cinfo->dev = dev;

        ret = info->desc->ops->chan_setup(cinfo, info->dev, tx);
        if (ret)
                return ret;

idr_alloc:
        ret = idr_alloc(idr, cinfo, prot_id, prot_id + 1, GFP_KERNEL);
        if (ret != prot_id) {
                dev_err(dev, "unable to allocate SCMI idr slot err %d\n", ret);
                return ret;
        }

        cinfo->handle = &info->handle;
        return 0;
}

static inline int
scmi_txrx_setup(struct scmi_info *info, struct device *dev, int prot_id)
{
        int ret = scmi_chan_setup(info, dev, prot_id, true);

        if (!ret) {
                /* Rx is optional, report only memory errors */
                ret = scmi_chan_setup(info, dev, prot_id, false);
                if (ret && ret != -ENOMEM)
                        ret = 0;
        }

        return ret;
}

/**
 * scmi_get_protocol_device  - Helper to get/create an SCMI device.
 *
 * @np: A device node representing a valid active protocols for the referred
 * SCMI instance.
 * @info: The referred SCMI instance for which we are getting/creating this
 * device.
 * @prot_id: The protocol ID.
 * @name: The device name.
 *
 * Referring to the specific SCMI instance identified by @info, this helper
 * takes care to return a properly initialized device matching the requested
 * @proto_id and @name: if device was still not existent it is created as a
 * child of the specified SCMI instance @info and its transport properly
 * initialized as usual.
 *
 * Return: A properly initialized scmi device, NULL otherwise.
 */
static inline struct scmi_device *
scmi_get_protocol_device(struct device_node *np, struct scmi_info *info,
                         int prot_id, const char *name)
{
        struct scmi_device *sdev;

        /* Already created for this parent SCMI instance ? */
        sdev = scmi_child_dev_find(info->dev, prot_id, name);
        if (sdev)
                return sdev;

        pr_debug("Creating SCMI device (%s) for protocol %x\n", name, prot_id);

        sdev = scmi_device_create(np, info->dev, prot_id, name);
        if (!sdev) {
                dev_err(info->dev, "failed to create %d protocol device\n",
                        prot_id);
                return NULL;
        }

        if (scmi_txrx_setup(info, &sdev->dev, prot_id)) {
                dev_err(&sdev->dev, "failed to setup transport\n");
                scmi_device_destroy(sdev);
                return NULL;
        }

        return sdev;
}

static inline void
scmi_create_protocol_device(struct device_node *np, struct scmi_info *info,
                            int prot_id, const char *name)
{
        struct scmi_device *sdev;

        sdev = scmi_get_protocol_device(np, info, prot_id, name);
        if (!sdev)
                return;

        /* setup handle now as the transport is ready */
        scmi_set_handle(sdev);
}

/**
 * scmi_create_protocol_devices  - Create devices for all pending requests for
 * this SCMI instance.
 *
 * @np: The device node describing the protocol
 * @info: The SCMI instance descriptor
 * @prot_id: The protocol ID
 *
 * All devices previously requested for this instance (if any) are found and
 * created by scanning the proper @&scmi_requested_devices entry.
 */
static void scmi_create_protocol_devices(struct device_node *np,
                                         struct scmi_info *info, int prot_id)
{
        struct list_head *phead;

        mutex_lock(&scmi_requested_devices_mtx);
        phead = idr_find(&scmi_requested_devices, prot_id);
        if (phead) {
                struct scmi_requested_dev *rdev;

                list_for_each_entry(rdev, phead, node)
                        scmi_create_protocol_device(np, info, prot_id,
                                                    rdev->id_table->name);
        }
        mutex_unlock(&scmi_requested_devices_mtx);
}

/**
 * scmi_protocol_device_request  - Helper to request a device
 *
 * @id_table: A protocol/name pair descriptor for the device to be created.
 *
 * This helper let an SCMI driver request specific devices identified by the
 * @id_table to be created for each active SCMI instance.
 *
 * The requested device name MUST NOT be already existent for any protocol;
 * at first the freshly requested @id_table is annotated in the IDR table
 * @scmi_requested_devices, then a matching device is created for each already
 * active SCMI instance. (if any)
 *
 * This way the requested device is created straight-away for all the already
 * initialized(probed) SCMI instances (handles) and it remains also annotated
 * as pending creation if the requesting SCMI driver was loaded before some
 * SCMI instance and related transports were available: when such late instance
 * is probed, its probe will take care to scan the list of pending requested
 * devices and create those on its own (see @scmi_create_protocol_devices and
 * its enclosing loop)
 *
 * Return: 0 on Success
 */
int scmi_protocol_device_request(const struct scmi_device_id *id_table)
{
        int ret = 0;
        unsigned int id = 0;
        struct list_head *head, *phead = NULL;
        struct scmi_requested_dev *rdev;
        struct scmi_info *info;

        pr_debug("Requesting SCMI device (%s) for protocol %x\n",
                 id_table->name, id_table->protocol_id);

        /*
         * Search for the matching protocol rdev list and then search
         * of any existent equally named device...fails if any duplicate found.
         */
        mutex_lock(&scmi_requested_devices_mtx);
        idr_for_each_entry(&scmi_requested_devices, head, id) {
                if (!phead) {
                        /* A list found registered in the IDR is never empty */
                        rdev = list_first_entry(head, struct scmi_requested_dev,
                                                node);
                        if (rdev->id_table->protocol_id ==
                            id_table->protocol_id)
                                phead = head;
                }
                list_for_each_entry(rdev, head, node) {
                        if (!strcmp(rdev->id_table->name, id_table->name)) {
                                pr_err("Ignoring duplicate request [%d] %s\n",
                                       rdev->id_table->protocol_id,
                                       rdev->id_table->name);
                                ret = -EINVAL;
                                goto out;
                        }
                }
        }

        /*
         * No duplicate found for requested id_table, so let's create a new
         * requested device entry for this new valid request.
         */
        rdev = kzalloc(sizeof(*rdev), GFP_KERNEL);
        if (!rdev) {
                ret = -ENOMEM;
                goto out;
        }
        rdev->id_table = id_table;

        /*
         * Append the new requested device table descriptor to the head of the
         * related protocol list, eventually creating such head if not already
         * there.
         */
        if (!phead) {
                phead = kzalloc(sizeof(*phead), GFP_KERNEL);
                if (!phead) {
                        kfree(rdev);
                        ret = -ENOMEM;
                        goto out;
                }
                INIT_LIST_HEAD(phead);

                ret = idr_alloc(&scmi_requested_devices, (void *)phead,
                                id_table->protocol_id,
                                id_table->protocol_id + 1, GFP_KERNEL);
                if (ret != id_table->protocol_id) {
                        pr_err("Failed to save SCMI device - ret:%d\n", ret);
                        kfree(rdev);
                        kfree(phead);
                        ret = -EINVAL;
                        goto out;
                }
                ret = 0;
        }
        list_add(&rdev->node, phead);

        /*
         * Now effectively create and initialize the requested device for every
         * already initialized SCMI instance which has registered the requested
         * protocol as a valid active one: i.e. defined in DT and supported by
         * current platform FW.
         */
        mutex_lock(&scmi_list_mutex);
        list_for_each_entry(info, &scmi_list, node) {
                struct device_node *child;

                child = idr_find(&info->active_protocols,
                                 id_table->protocol_id);
                if (child) {
                        struct scmi_device *sdev;

                        sdev = scmi_get_protocol_device(child, info,
                                                        id_table->protocol_id,
                                                        id_table->name);
                        if (sdev) {
                                /* Set handle if not already set: device existed */
                                if (!sdev->handle)
                                        sdev->handle =
                                                scmi_handle_get_from_info_unlocked(info);
                                /* Relink consumer and suppliers */
                                if (sdev->handle)
                                        scmi_device_link_add(&sdev->dev,
                                                             sdev->handle->dev);
                        }
                } else {
                        dev_err(info->dev,
                                "Failed. SCMI protocol %d not active.\n",
                                id_table->protocol_id);
                }
        }
        mutex_unlock(&scmi_list_mutex);

out:
        mutex_unlock(&scmi_requested_devices_mtx);

        return ret;
}

/**
 * scmi_protocol_device_unrequest  - Helper to unrequest a device
 *
 * @id_table: A protocol/name pair descriptor for the device to be unrequested.
 *
 * An helper to let an SCMI driver release its request about devices; note that
 * devices are created and initialized once the first SCMI driver request them
 * but they destroyed only on SCMI core unloading/unbinding.
 *
 * The current SCMI transport layer uses such devices as internal references and
 * as such they could be shared as same transport between multiple drivers so
 * that cannot be safely destroyed till the whole SCMI stack is removed.
 * (unless adding further burden of refcounting.)
 */
void scmi_protocol_device_unrequest(const struct scmi_device_id *id_table)
{
        struct list_head *phead;

        pr_debug("Unrequesting SCMI device (%s) for protocol %x\n",
                 id_table->name, id_table->protocol_id);

        mutex_lock(&scmi_requested_devices_mtx);
        phead = idr_find(&scmi_requested_devices, id_table->protocol_id);
        if (phead) {
                struct scmi_requested_dev *victim, *tmp;

                list_for_each_entry_safe(victim, tmp, phead, node) {
                        if (!strcmp(victim->id_table->name, id_table->name)) {
                                list_del(&victim->node);
                                kfree(victim);
                                break;
                        }
                }

                if (list_empty(phead)) {
                        idr_remove(&scmi_requested_devices,
                                   id_table->protocol_id);
                        kfree(phead);
                }
        }
        mutex_unlock(&scmi_requested_devices_mtx);
}

static int scmi_cleanup_txrx_channels(struct scmi_info *info)
{
        int ret;
        struct idr *idr = &info->tx_idr;

        ret = idr_for_each(idr, info->desc->ops->chan_free, idr);
        idr_destroy(&info->tx_idr);

        idr = &info->rx_idr;
        ret = idr_for_each(idr, info->desc->ops->chan_free, idr);
        idr_destroy(&info->rx_idr);

        return ret;
}

static int scmi_probe(struct platform_device *pdev)
{
        int ret;
        struct scmi_handle *handle;
        const struct scmi_desc *desc;
        struct scmi_info *info;
        struct device *dev = &pdev->dev;
        struct device_node *child, *np = dev->of_node;

        desc = of_device_get_match_data(dev);
        if (!desc)
                return -EINVAL;

        info = devm_kzalloc(dev, sizeof(*info), GFP_KERNEL);
        if (!info)
                return -ENOMEM;

        info->dev = dev;
        info->desc = desc;
        INIT_LIST_HEAD(&info->node);
        idr_init(&info->protocols);
        mutex_init(&info->protocols_mtx);
        idr_init(&info->active_protocols);

        platform_set_drvdata(pdev, info);
        idr_init(&info->tx_idr);
        idr_init(&info->rx_idr);

        handle = &info->handle;
        handle->dev = info->dev;
        handle->version = &info->version;
        handle->devm_protocol_get = scmi_devm_protocol_get;
        handle->devm_protocol_put = scmi_devm_protocol_put;

        if (desc->ops->link_supplier) {
                ret = desc->ops->link_supplier(dev);
                if (ret)
                        return ret;
        }

        ret = scmi_txrx_setup(info, dev, SCMI_PROTOCOL_BASE);
        if (ret)
                return ret;

        ret = scmi_xfer_info_init(info);
        if (ret)
                goto clear_txrx_setup;

        if (scmi_notification_init(handle))
                dev_err(dev, "SCMI Notifications NOT available.\n");

        /*
         * Trigger SCMI Base protocol initialization.
         * It's mandatory and won't be ever released/deinit until the
         * SCMI stack is shutdown/unloaded as a whole.
         */
        ret = scmi_protocol_acquire(handle, SCMI_PROTOCOL_BASE);
        if (ret) {
                dev_err(dev, "unable to communicate with SCMI\n");
                goto notification_exit;
        }

        mutex_lock(&scmi_list_mutex);
        list_add_tail(&info->node, &scmi_list);
        mutex_unlock(&scmi_list_mutex);

        for_each_available_child_of_node(np, child) {
                u32 prot_id;

                if (of_property_read_u32(child, "reg", &prot_id))
                        continue;

                if (!FIELD_FIT(MSG_PROTOCOL_ID_MASK, prot_id))
                        dev_err(dev, "Out of range protocol %d\n", prot_id);

                if (!scmi_is_protocol_implemented(handle, prot_id)) {
                        dev_err(dev, "SCMI protocol %d not implemented\n",
                                prot_id);
                        continue;
                }

                /*
                 * Save this valid DT protocol descriptor amongst
                 * @active_protocols for this SCMI instance/
                 */
                ret = idr_alloc(&info->active_protocols, child,
                                prot_id, prot_id + 1, GFP_KERNEL);
                if (ret != prot_id) {
                        dev_err(dev, "SCMI protocol %d already activated. Skip\n",
                                prot_id);
                        continue;
                }

                of_node_get(child);
                scmi_create_protocol_devices(child, info, prot_id);
        }

        return 0;

notification_exit:
        scmi_notification_exit(&info->handle);
clear_txrx_setup:
        scmi_cleanup_txrx_channels(info);
        return ret;
}

void scmi_free_channel(struct scmi_chan_info *cinfo, struct idr *idr, int id)
{
        idr_remove(idr, id);
}

static int scmi_remove(struct platform_device *pdev)
{
        int ret, id;
        struct scmi_info *info = platform_get_drvdata(pdev);
        struct device_node *child;

        mutex_lock(&scmi_list_mutex);
        if (info->users)
                dev_warn(&pdev->dev,
                         "Still active SCMI users will be forcibly unbound.\n");
        list_del(&info->node);
        mutex_unlock(&scmi_list_mutex);

        scmi_notification_exit(&info->handle);

        mutex_lock(&info->protocols_mtx);
        idr_destroy(&info->protocols);
        mutex_unlock(&info->protocols_mtx);

        idr_for_each_entry(&info->active_protocols, child, id)
                of_node_put(child);
        idr_destroy(&info->active_protocols);

        /* Safe to free channels since no more users */
        ret = scmi_cleanup_txrx_channels(info);
        if (ret)
                dev_warn(&pdev->dev, "Failed to cleanup SCMI channels.\n");

        return 0;
}

static ssize_t protocol_version_show(struct device *dev,
                                     struct device_attribute *attr, char *buf)
{
        struct scmi_info *info = dev_get_drvdata(dev);

        return sprintf(buf, "%u.%u\n", info->version.major_ver,
                       info->version.minor_ver);
}
static DEVICE_ATTR_RO(protocol_version);

static ssize_t firmware_version_show(struct device *dev,
                                     struct device_attribute *attr, char *buf)
{
        struct scmi_info *info = dev_get_drvdata(dev);

        return sprintf(buf, "0x%x\n", info->version.impl_ver);
}
static DEVICE_ATTR_RO(firmware_version);

static ssize_t vendor_id_show(struct device *dev,
                              struct device_attribute *attr, char *buf)
{
        struct scmi_info *info = dev_get_drvdata(dev);

        return sprintf(buf, "%s\n", info->version.vendor_id);
}
static DEVICE_ATTR_RO(vendor_id);

static ssize_t sub_vendor_id_show(struct device *dev,
                                  struct device_attribute *attr, char *buf)
{
        struct scmi_info *info = dev_get_drvdata(dev);

        return sprintf(buf, "%s\n", info->version.sub_vendor_id);
}
static DEVICE_ATTR_RO(sub_vendor_id);

static struct attribute *versions_attrs[] = {
        &dev_attr_firmware_version.attr,
        &dev_attr_protocol_version.attr,
        &dev_attr_vendor_id.attr,
        &dev_attr_sub_vendor_id.attr,
        NULL,
};
ATTRIBUTE_GROUPS(versions);

/* Each compatible listed below must have descriptor associated with it */
static const struct of_device_id scmi_of_match[] = {
#ifdef CONFIG_ARM_SCMI_TRANSPORT_MAILBOX
        { .compatible = "arm,scmi", .data = &scmi_mailbox_desc },
#endif
#ifdef CONFIG_ARM_SCMI_TRANSPORT_SMC
        { .compatible = "arm,scmi-smc", .data = &scmi_smc_desc},
#endif
#ifdef CONFIG_ARM_SCMI_TRANSPORT_VIRTIO
        { .compatible = "arm,scmi-virtio", .data = &scmi_virtio_desc},
#endif
        { /* Sentinel */ },
};

MODULE_DEVICE_TABLE(of, scmi_of_match);

static struct platform_driver scmi_driver = {
        .driver = {
                   .name = "arm-scmi",
                   .suppress_bind_attrs = true,
                   .of_match_table = scmi_of_match,
                   .dev_groups = versions_groups,
                   },
        .probe = scmi_probe,
        .remove = scmi_remove,
};

/**
 * __scmi_transports_setup  - Common helper to call transport-specific
 * .init/.exit code if provided.
 *
 * @init: A flag to distinguish between init and exit.
 *
 * Note that, if provided, we invoke .init/.exit functions for all the
 * transports currently compiled in.
 *
 * Return: 0 on Success.
 */
static inline int __scmi_transports_setup(bool init)
{
        int ret = 0;
        const struct of_device_id *trans;

        for (trans = scmi_of_match; trans->data; trans++) {
                const struct scmi_desc *tdesc = trans->data;

                if ((init && !tdesc->transport_init) ||
                    (!init && !tdesc->transport_exit))
                        continue;

                if (init)
                        ret = tdesc->transport_init();
                else
                        tdesc->transport_exit();

                if (ret) {
                        pr_err("SCMI transport %s FAILED initialization!\n",
                               trans->compatible);
                        break;
                }
        }

        return ret;
}

static int __init scmi_transports_init(void)
{
        return __scmi_transports_setup(true);
}

static void __exit scmi_transports_exit(void)
{
        __scmi_transports_setup(false);
}

static int __init scmi_driver_init(void)
{
        int ret;

        /* Bail out if no SCMI transport was configured */
        if (WARN_ON(!IS_ENABLED(CONFIG_ARM_SCMI_HAVE_TRANSPORT)))
                return -EINVAL;

        scmi_bus_init();

        /* Initialize any compiled-in transport which provided an init/exit */
        ret = scmi_transports_init();
        if (ret)
                return ret;

        scmi_base_register();

        scmi_clock_register();
        scmi_perf_register();
        scmi_power_register();
        scmi_reset_register();
        scmi_sensors_register();
        scmi_voltage_register();
        scmi_system_register();

        return platform_driver_register(&scmi_driver);
}
subsys_initcall(scmi_driver_init);

static void __exit scmi_driver_exit(void)
{
        scmi_base_unregister();

        scmi_clock_unregister();
        scmi_perf_unregister();
        scmi_power_unregister();
        scmi_reset_unregister();
        scmi_sensors_unregister();
        scmi_voltage_unregister();
        scmi_system_unregister();

        scmi_bus_exit();

        scmi_transports_exit();

        platform_driver_unregister(&scmi_driver);
}
module_exit(scmi_driver_exit);

MODULE_ALIAS("platform:arm-scmi");
MODULE_AUTHOR("Sudeep Holla <sudeep.holla@arm.com>");
MODULE_DESCRIPTION("ARM SCMI protocol driver");
MODULE_LICENSE("GPL v2");