firmware: arm_scmi: Add configurable polling mode for transports

SCMI communications along TX channels can optionally be provided of a
completion interrupt; when such interrupt is not available, command
transactions should rely on polling, where the SCMI core takes care to
repeatedly evaluate the transport-specific .poll_done() function, if
available, to determine if and when a request was fully completed or
timed out.

Such mechanism is already present and working on a single transfer base:
SCMI protocols can indeed enable hdr.poll_completion on specific commands
ahead of each transfer and cause that transaction to be handled with
polling.

Introduce a couple of flags to be able to enforce such polling behaviour
globally at will:

 - scmi_desc.force_polling: to statically switch the whole transport to
   polling mode.

 - scmi_chan_info.no_completion_irq: to switch a single channel dynamically
   to polling mode if, at runtime, is determined that no completion
   interrupt was available for such channel.

Link: https://lore.kernel.org/r/20211220195646.44498-2-cristian.marussi@arm.com
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

diff --git a/drivers/firmware/arm_scmi/common.h b/drivers/firmware/arm_scmi/common.h
index 6438b52..652e5d9 100644 (file)
--- a/drivers/firmware/arm_scmi/common.h
+++ b/drivers/firmware/arm_scmi/common.h
@@ -339,11 +339,16 @@ void scmi_protocol_release(const struct scmi_handle *handle, u8 protocol_id);
  * @dev: Reference to device in the SCMI hierarchy corresponding to this
  *      channel
  * @handle: Pointer to SCMI entity handle
+ * @no_completion_irq: Flag to indicate that this channel has no completion
+ *                    interrupt mechanism for synchronous commands.
+ *                    This can be dynamically set by transports at run-time
+ *                    inside their provided .chan_setup().
  * @transport_info: Transport layer related information
  */
 struct scmi_chan_info {
        struct device *dev;
        struct scmi_handle *handle;
+       bool no_completion_irq;
        void *transport_info;
 };
 
@@ -402,6 +407,8 @@ struct scmi_device *scmi_child_dev_find(struct device *parent,
  *     be pending simultaneously in the system. May be overridden by the
  *     get_max_msg op.
  * @max_msg_size: Maximum size of data per message that can be handled.
+ * @force_polling: Flag to force this whole transport to use SCMI core polling
+ *                mechanism instead of completion interrupts even if available.
  */
 struct scmi_desc {
        int (*transport_init)(void);
@@ -410,6 +417,7 @@ struct scmi_desc {
        int max_rx_timeout_ms;
        int max_msg;
        int max_msg_size;
+       const bool force_polling;
 };
 
 #ifdef CONFIG_ARM_SCMI_TRANSPORT_MAILBOX

diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
index 476b918..7579f54 100644 (file)
--- a/drivers/firmware/arm_scmi/driver.c
+++ b/drivers/firmware/arm_scmi/driver.c
@@ -609,6 +609,24 @@ static inline void scmi_clear_channel(struct scmi_info *info,
                info->desc->ops->clear_channel(cinfo);
 }
 
+static inline bool is_polling_required(struct scmi_chan_info *cinfo,
+                                      struct scmi_info *info)
+{
+       return cinfo->no_completion_irq || info->desc->force_polling;
+}
+
+static inline bool is_transport_polling_capable(struct scmi_info *info)
+{
+       return info->desc->ops->poll_done;
+}
+
+static inline bool is_polling_enabled(struct scmi_chan_info *cinfo,
+                                     struct scmi_info *info)
+{
+       return is_polling_required(cinfo, info) &&
+               is_transport_polling_capable(info);
+}
+
 static void scmi_handle_notification(struct scmi_chan_info *cinfo,
                                     u32 msg_hdr, void *priv)
 {
@@ -817,6 +835,7 @@ static int do_xfer(const struct scmi_protocol_handle *ph,
        struct device *dev = info->dev;
        struct scmi_chan_info *cinfo;
 
+       /* Check for polling request on custom command xfers at first */
        if (xfer->hdr.poll_completion && !info->desc->ops->poll_done) {
                dev_warn_once(dev,
                              "Polling mode is not supported by transport.\n");
@@ -827,6 +846,10 @@ static int do_xfer(const struct scmi_protocol_handle *ph,
        if (unlikely(!cinfo))
                return -EINVAL;
 
+       /* True ONLY if also supported by transport. */
+       if (is_polling_enabled(cinfo, info))
+               xfer->hdr.poll_completion = true;
+
        /*
         * Initialise protocol id now from protocol handle to avoid it being
         * overridden by mistake (or malice) by the protocol code mangling with
@@ -1527,6 +1550,16 @@ static int scmi_chan_setup(struct scmi_info *info, struct device *dev,
        if (ret)
                return ret;
 
+       if (tx && is_polling_required(cinfo, info)) {
+               if (is_transport_polling_capable(info))
+                       dev_info(dev,
+                                "Enabled polling mode TX channel - prot_id:%d\n",
+                                prot_id);
+               else
+                       dev_warn(dev,
+                                "Polling mode NOT supported by transport.\n");
+       }
+
 idr_alloc:
        ret = idr_alloc(idr, cinfo, prot_id, prot_id + 1, GFP_KERNEL);
        if (ret != prot_id) {