* Virtio Transport driver for Arm System Control and Management Interface
* (SCMI).
*
- * Copyright (C) 2020-2021 OpenSynergy.
- * Copyright (C) 2021 ARM Ltd.
+ * Copyright (C) 2020-2022 OpenSynergy.
+ * Copyright (C) 2021-2022 ARM Ltd.
*/
/**
* @cinfo: SCMI Tx or Rx channel
* @free_lock: Protects access to the @free_list.
* @free_list: List of unused scmi_vio_msg, maintained for Tx channels only
+ * @deferred_tx_work: Worker for TX deferred replies processing
+ * @deferred_tx_wq: Workqueue for TX deferred replies
+ * @pending_lock: Protects access to the @pending_cmds_list.
+ * @pending_cmds_list: List of pre-fetched commands queueud for later processing
* @is_rx: Whether channel is an Rx channel
* @max_msg: Maximum number of pending messages for this channel.
- * @lock: Protects access to all members except users, free_list.
+ * @lock: Protects access to all members except users, free_list and
+ * pending_cmds_list.
* @shutdown_done: A reference to a completion used when freeing this channel.
* @users: A reference count to currently active users of this channel.
*/
/* lock to protect access to the free list. */
spinlock_t free_lock;
struct list_head free_list;
+ /* lock to protect access to the pending list. */
+ spinlock_t pending_lock;
+ struct list_head pending_cmds_list;
+ struct work_struct deferred_tx_work;
+ struct workqueue_struct *deferred_tx_wq;
bool is_rx;
unsigned int max_msg;
- /* lock to protect access to all members except users, free_list */
+ /*
+ * Lock to protect access to all members except users, free_list and
+ * pending_cmds_list
+ */
spinlock_t lock;
struct completion *shutdown_done;
refcount_t users;
};
+enum poll_states {
+ VIO_MSG_NOT_POLLED,
+ VIO_MSG_POLL_TIMEOUT,
+ VIO_MSG_POLLING,
+ VIO_MSG_POLL_DONE,
+};
+
/**
* struct scmi_vio_msg - Transport PDU information
*
* @input: SDU used for (delayed) responses and notifications
* @list: List which scmi_vio_msg may be part of
* @rx_len: Input SDU size in bytes, once input has been received
+ * @poll_idx: Last used index registered for polling purposes if this message
+ * transaction reply was configured for polling.
+ * @poll_status: Polling state for this message.
+ * @poll_lock: A lock to protect @poll_status
+ * @users: A reference count to track this message users and avoid premature
+ * freeing (and reuse) when polling and IRQ execution paths interleave.
*/
struct scmi_vio_msg {
struct scmi_msg_payld *request;
struct scmi_msg_payld *input;
struct list_head list;
unsigned int rx_len;
+ unsigned int poll_idx;
+ enum poll_states poll_status;
+ /* Lock to protect access to poll_status */
+ spinlock_t poll_lock;
+ refcount_t users;
};
/* Only one SCMI VirtIO device can possibly exist */
{
unsigned long flags;
DECLARE_COMPLETION_ONSTACK(vioch_shutdown_done);
+ void *deferred_wq = NULL;
/*
* Prepare to wait for the last release if not already released
spin_unlock_irqrestore(&vioch->lock, flags);
return;
}
+
vioch->shutdown_done = &vioch_shutdown_done;
virtio_break_device(vioch->vqueue->vdev);
+ if (!vioch->is_rx && vioch->deferred_tx_wq) {
+ deferred_wq = vioch->deferred_tx_wq;
+ /* Cannot be kicked anymore after this...*/
+ vioch->deferred_tx_wq = NULL;
+ }
spin_unlock_irqrestore(&vioch->lock, flags);
+ if (deferred_wq)
+ destroy_workqueue(deferred_wq);
+
scmi_vio_channel_release(vioch);
/* Let any possibly concurrent RX path release the channel */
list_del_init(&msg->list);
spin_unlock_irqrestore(&vioch->free_lock, flags);
+ /* Still no users, no need to acquire poll_lock */
+ msg->poll_status = VIO_MSG_NOT_POLLED;
+ refcount_set(&msg->users, 1);
+
return msg;
}
+static inline bool scmi_vio_msg_acquire(struct scmi_vio_msg *msg)
+{
+ return refcount_inc_not_zero(&msg->users);
+}
+
/* Assumes to be called with vio channel acquired already */
-static void scmi_virtio_put_free_msg(struct scmi_vio_channel *vioch,
- struct scmi_vio_msg *msg)
+static inline bool scmi_vio_msg_release(struct scmi_vio_channel *vioch,
+ struct scmi_vio_msg *msg)
{
- unsigned long flags;
+ bool ret;
- spin_lock_irqsave(&vioch->free_lock, flags);
- list_add_tail(&msg->list, &vioch->free_list);
- spin_unlock_irqrestore(&vioch->free_lock, flags);
+ ret = refcount_dec_and_test(&msg->users);
+ if (ret) {
+ unsigned long flags;
+
+ spin_lock_irqsave(&vioch->free_lock, flags);
+ list_add_tail(&msg->list, &vioch->free_list);
+ spin_unlock_irqrestore(&vioch->free_lock, flags);
+ }
+
+ return ret;
}
static bool scmi_vio_have_vq_rx(struct virtio_device *vdev)
if (vioch->is_rx)
scmi_vio_feed_vq_rx(vioch, msg);
else
- scmi_virtio_put_free_msg(vioch, msg);
+ scmi_vio_msg_release(vioch, msg);
}
static void scmi_vio_complete_cb(struct virtqueue *vqueue)
virtqueue_disable_cb(vqueue);
cb_enabled = false;
}
+
msg = virtqueue_get_buf(vqueue, &length);
if (!msg) {
if (virtqueue_enable_cb(vqueue)) {
}
}
+static void scmi_vio_deferred_tx_worker(struct work_struct *work)
+{
+ unsigned long flags;
+ struct scmi_vio_channel *vioch;
+ struct scmi_vio_msg *msg, *tmp;
+
+ vioch = container_of(work, struct scmi_vio_channel, deferred_tx_work);
+
+ if (!scmi_vio_channel_acquire(vioch))
+ return;
+
+ /*
+ * Process pre-fetched messages: these could be non-polled messages or
+ * late timed-out replies to polled messages dequeued by chance while
+ * polling for some other messages: this worker is in charge to process
+ * the valid non-expired messages and anyway finally free all of them.
+ */
+ spin_lock_irqsave(&vioch->pending_lock, flags);
+
+ /* Scan the list of possibly pre-fetched messages during polling. */
+ list_for_each_entry_safe(msg, tmp, &vioch->pending_cmds_list, list) {
+ list_del(&msg->list);
+
+ /*
+ * Channel is acquired here (cannot vanish) and this message
+ * is no more processed elsewhere so no poll_lock needed.
+ */
+ if (msg->poll_status == VIO_MSG_NOT_POLLED)
+ scmi_rx_callback(vioch->cinfo,
+ msg_read_header(msg->input), msg);
+
+ /* Free the processed message once done */
+ scmi_vio_msg_release(vioch, msg);
+ }
+
+ spin_unlock_irqrestore(&vioch->pending_lock, flags);
+
+ /* Process possibly still pending messages */
+ scmi_vio_complete_cb(vioch->vqueue);
+
+ scmi_vio_channel_release(vioch);
+}
+
static const char *const scmi_vio_vqueue_names[] = { "tx", "rx" };
static vq_callback_t *scmi_vio_complete_callbacks[] = {
vioch = &((struct scmi_vio_channel *)scmi_vdev->priv)[index];
+ /* Setup a deferred worker for polling. */
+ if (tx && !vioch->deferred_tx_wq) {
+ vioch->deferred_tx_wq =
+ alloc_workqueue(dev_name(&scmi_vdev->dev),
+ WQ_UNBOUND | WQ_FREEZABLE | WQ_SYSFS,
+ 0);
+ if (!vioch->deferred_tx_wq)
+ return -ENOMEM;
+
+ INIT_WORK(&vioch->deferred_tx_work,
+ scmi_vio_deferred_tx_worker);
+ }
+
for (i = 0; i < vioch->max_msg; i++) {
struct scmi_vio_msg *msg;
GFP_KERNEL);
if (!msg->request)
return -ENOMEM;
+ spin_lock_init(&msg->poll_lock);
+ refcount_set(&msg->users, 1);
}
msg->input = devm_kzalloc(cinfo->dev, VIRTIO_SCMI_MAX_PDU_SIZE,
spin_lock_irqsave(&vioch->lock, flags);
+ /*
+ * If polling was requested for this transaction:
+ * - retrieve last used index (will be used as polling reference)
+ * - bind the polled message to the xfer via .priv
+ * - grab an additional msg refcount for the poll-path
+ */
+ if (xfer->hdr.poll_completion) {
+ msg->poll_idx = virtqueue_enable_cb_prepare(vioch->vqueue);
+ /* Still no users, no need to acquire poll_lock */
+ msg->poll_status = VIO_MSG_POLLING;
+ scmi_vio_msg_acquire(msg);
+ /* Ensure initialized msg is visibly bound to xfer */
+ smp_store_mb(xfer->priv, msg);
+ }
+
rc = virtqueue_add_sgs(vioch->vqueue, sgs, 1, 1, msg, GFP_ATOMIC);
if (rc)
dev_err(vioch->cinfo->dev,
spin_unlock_irqrestore(&vioch->lock, flags);
- if (rc)
- scmi_virtio_put_free_msg(vioch, msg);
+ if (rc) {
+ /* Ensure order between xfer->priv clear and vq feeding */
+ smp_store_mb(xfer->priv, NULL);
+ if (xfer->hdr.poll_completion)
+ scmi_vio_msg_release(vioch, msg);
+ scmi_vio_msg_release(vioch, msg);
+ }
scmi_vio_channel_release(vioch);
{
struct scmi_vio_msg *msg = xfer->priv;
- if (msg) {
+ if (msg)
msg_fetch_response(msg->input, msg->rx_len, xfer);
- xfer->priv = NULL;
- }
}
static void virtio_fetch_notification(struct scmi_chan_info *cinfo,
{
struct scmi_vio_msg *msg = xfer->priv;
- if (msg) {
+ if (msg)
msg_fetch_notification(msg->input, msg->rx_len, max_len, xfer);
- xfer->priv = NULL;
+}
+
+/**
+ * virtio_mark_txdone - Mark transmission done
+ *
+ * Free only completed polling transfer messages.
+ *
+ * Note that in the SCMI VirtIO transport we never explicitly release still
+ * outstanding but timed-out messages by forcibly re-adding them to the
+ * free-list inside the TX code path; we instead let IRQ/RX callbacks, or the
+ * TX deferred worker, eventually clean up such messages once, finally, a late
+ * reply is received and discarded (if ever).
+ *
+ * This approach was deemed preferable since those pending timed-out buffers are
+ * still effectively owned by the SCMI platform VirtIO device even after timeout
+ * expiration: forcibly freeing and reusing them before they had been returned
+ * explicitly by the SCMI platform could lead to subtle bugs due to message
+ * corruption.
+ * An SCMI platform VirtIO device which never returns message buffers is
+ * anyway broken and it will quickly lead to exhaustion of available messages.
+ *
+ * For this same reason, here, we take care to free only the polled messages
+ * that had been somehow replied (only if not by chance already processed on the
+ * IRQ path - the initial scmi_vio_msg_release() takes care of this) and also
+ * any timed-out polled message if that indeed appears to have been at least
+ * dequeued from the virtqueues (VIO_MSG_POLL_DONE): this is needed since such
+ * messages won't be freed elsewhere. Any other polled message is marked as
+ * VIO_MSG_POLL_TIMEOUT.
+ *
+ * Possible late replies to timed-out polled messages will be eventually freed
+ * by RX callbacks if delivered on the IRQ path or by the deferred TX worker if
+ * dequeued on some other polling path.
+ *
+ * @cinfo: SCMI channel info
+ * @ret: Transmission return code
+ * @xfer: Transfer descriptor
+ */
+static void virtio_mark_txdone(struct scmi_chan_info *cinfo, int ret,
+ struct scmi_xfer *xfer)
+{
+ unsigned long flags;
+ struct scmi_vio_channel *vioch = cinfo->transport_info;
+ struct scmi_vio_msg *msg = xfer->priv;
+
+ if (!msg || !scmi_vio_channel_acquire(vioch))
+ return;
+
+ /* Ensure msg is unbound from xfer anyway at this point */
+ smp_store_mb(xfer->priv, NULL);
+
+ /* Must be a polled xfer and not already freed on the IRQ path */
+ if (!xfer->hdr.poll_completion || scmi_vio_msg_release(vioch, msg)) {
+ scmi_vio_channel_release(vioch);
+ return;
}
+
+ spin_lock_irqsave(&msg->poll_lock, flags);
+ /* Do not free timedout polled messages only if still inflight */
+ if (ret != -ETIMEDOUT || msg->poll_status == VIO_MSG_POLL_DONE)
+ scmi_vio_msg_release(vioch, msg);
+ else if (msg->poll_status == VIO_MSG_POLLING)
+ msg->poll_status = VIO_MSG_POLL_TIMEOUT;
+ spin_unlock_irqrestore(&msg->poll_lock, flags);
+
+ scmi_vio_channel_release(vioch);
+}
+
+/**
+ * virtio_poll_done - Provide polling support for VirtIO transport
+ *
+ * @cinfo: SCMI channel info
+ * @xfer: Reference to the transfer being poll for.
+ *
+ * VirtIO core provides a polling mechanism based only on last used indexes:
+ * this means that it is possible to poll the virtqueues waiting for something
+ * new to arrive from the host side, but the only way to check if the freshly
+ * arrived buffer was indeed what we were waiting for is to compare the newly
+ * arrived message descriptor with the one we are polling on.
+ *
+ * As a consequence it can happen to dequeue something different from the buffer
+ * we were poll-waiting for: if that is the case such early fetched buffers are
+ * then added to a the @pending_cmds_list list for later processing by a
+ * dedicated deferred worker.
+ *
+ * So, basically, once something new is spotted we proceed to de-queue all the
+ * freshly received used buffers until we found the one we were polling on, or,
+ * we have 'seemingly' emptied the virtqueue; if some buffers are still pending
+ * in the vqueue at the end of the polling loop (possible due to inherent races
+ * in virtqueues handling mechanisms), we similarly kick the deferred worker
+ * and let it process those, to avoid indefinitely looping in the .poll_done
+ * busy-waiting helper.
+ *
+ * Finally, we delegate to the deferred worker also the final free of any timed
+ * out reply to a polled message that we should dequeue.
+ *
+ * Note that, since we do NOT have per-message suppress notification mechanism,
+ * the message we are polling for could be alternatively delivered via usual
+ * IRQs callbacks on another core which happened to have IRQs enabled while we
+ * are actively polling for it here: in such a case it will be handled as such
+ * by scmi_rx_callback() and the polling loop in the SCMI Core TX path will be
+ * transparently terminated anyway.
+ *
+ * Return: True once polling has successfully completed.
+ */
+static bool virtio_poll_done(struct scmi_chan_info *cinfo,
+ struct scmi_xfer *xfer)
+{
+ bool pending, found = false;
+ unsigned int length, any_prefetched = 0;
+ unsigned long flags;
+ struct scmi_vio_msg *next_msg, *msg = xfer->priv;
+ struct scmi_vio_channel *vioch = cinfo->transport_info;
+
+ if (!msg)
+ return true;
+
+ /*
+ * Processed already by other polling loop on another CPU ?
+ *
+ * Note that this message is acquired on the poll path so cannot vanish
+ * while inside this loop iteration even if concurrently processed on
+ * the IRQ path.
+ *
+ * Avoid to acquire poll_lock since polled_status can be changed
+ * in a relevant manner only later in this same thread of execution:
+ * any other possible changes made concurrently by other polling loops
+ * or by a reply delivered on the IRQ path have no meaningful impact on
+ * this loop iteration: in other words it is harmless to allow this
+ * possible race but let has avoid spinlocking with irqs off in this
+ * initial part of the polling loop.
+ */
+ if (msg->poll_status == VIO_MSG_POLL_DONE)
+ return true;
+
+ if (!scmi_vio_channel_acquire(vioch))
+ return true;
+
+ /* Has cmdq index moved at all ? */
+ pending = virtqueue_poll(vioch->vqueue, msg->poll_idx);
+ if (!pending) {
+ scmi_vio_channel_release(vioch);
+ return false;
+ }
+
+ spin_lock_irqsave(&vioch->lock, flags);
+ virtqueue_disable_cb(vioch->vqueue);
+
+ /*
+ * Process all new messages till the polled-for message is found OR
+ * the vqueue is empty.
+ */
+ while ((next_msg = virtqueue_get_buf(vioch->vqueue, &length))) {
+ bool next_msg_done = false;
+
+ /*
+ * Mark any dequeued buffer message as VIO_MSG_POLL_DONE so
+ * that can be properly freed even on timeout in mark_txdone.
+ */
+ spin_lock(&next_msg->poll_lock);
+ if (next_msg->poll_status == VIO_MSG_POLLING) {
+ next_msg->poll_status = VIO_MSG_POLL_DONE;
+ next_msg_done = true;
+ }
+ spin_unlock(&next_msg->poll_lock);
+
+ next_msg->rx_len = length;
+ /* Is the message we were polling for ? */
+ if (next_msg == msg) {
+ found = true;
+ break;
+ } else if (next_msg_done) {
+ /* Skip the rest if this was another polled msg */
+ continue;
+ }
+
+ /*
+ * Enqueue for later processing any non-polled message and any
+ * timed-out polled one that we happen to have dequeued.
+ */
+ spin_lock(&next_msg->poll_lock);
+ if (next_msg->poll_status == VIO_MSG_NOT_POLLED ||
+ next_msg->poll_status == VIO_MSG_POLL_TIMEOUT) {
+ spin_unlock(&next_msg->poll_lock);
+
+ any_prefetched++;
+ spin_lock(&vioch->pending_lock);
+ list_add_tail(&next_msg->list,
+ &vioch->pending_cmds_list);
+ spin_unlock(&vioch->pending_lock);
+ } else {
+ spin_unlock(&next_msg->poll_lock);
+ }
+ }
+
+ /*
+ * When the polling loop has successfully terminated if something
+ * else was queued in the meantime, it will be served by a deferred
+ * worker OR by the normal IRQ/callback OR by other poll loops.
+ *
+ * If we are still looking for the polled reply, the polling index has
+ * to be updated to the current vqueue last used index.
+ */
+ if (found) {
+ pending = !virtqueue_enable_cb(vioch->vqueue);
+ } else {
+ msg->poll_idx = virtqueue_enable_cb_prepare(vioch->vqueue);
+ pending = virtqueue_poll(vioch->vqueue, msg->poll_idx);
+ }
+
+ if (vioch->deferred_tx_wq && (any_prefetched || pending))
+ queue_work(vioch->deferred_tx_wq, &vioch->deferred_tx_work);
+
+ spin_unlock_irqrestore(&vioch->lock, flags);
+
+ scmi_vio_channel_release(vioch);
+
+ return found;
}
static const struct scmi_transport_ops scmi_virtio_ops = {
.send_message = virtio_send_message,
.fetch_response = virtio_fetch_response,
.fetch_notification = virtio_fetch_notification,
+ .mark_txdone = virtio_mark_txdone,
+ .poll_done = virtio_poll_done,
};
static int scmi_vio_probe(struct virtio_device *vdev)
spin_lock_init(&channels[i].lock);
spin_lock_init(&channels[i].free_lock);
INIT_LIST_HEAD(&channels[i].free_list);
+ spin_lock_init(&channels[i].pending_lock);
+ INIT_LIST_HEAD(&channels[i].pending_cmds_list);
channels[i].vqueue = vqs[i];
sz = virtqueue_get_vring_size(channels[i].vqueue);
.max_rx_timeout_ms = VIRTIO_MAX_RX_TIMEOUT_MS,
.max_msg = 0, /* overridden by virtio_get_max_msg() */
.max_msg_size = VIRTIO_SCMI_MAX_MSG_SIZE,
+ .atomic_enabled = IS_ENABLED(CONFIG_ARM_SCMI_TRANSPORT_VIRTIO_ATOMIC_ENABLE),
};
projects / platform / kernel / linux-rpi.git / commitdiff