[PATCH] firmware: arm_scmi: Queue in scmi layer for mailbox implementation

[Justin Chen]

The mailbox layer has its own queue. However this confuses the per
message timeouts since the clock starts ticking the moment the messages
get queued up. So all messages in the queue have there timeout clocks
ticking instead of only the message inflight. To fix this, lets move the
queue back into the SCMI layer.

Signed-off-by: Justin Chen <justin.chen at broadcom.com>
---
 .../firmware/arm_scmi/transports/mailbox.c    | 21 +++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/drivers/firmware/arm_scmi/transports/mailbox.c b/drivers/firmware/arm_scmi/transports/mailbox.c
index 1a754dee24f7..30bc2865582f 100644
--- a/drivers/firmware/arm_scmi/transports/mailbox.c
+++ b/drivers/firmware/arm_scmi/transports/mailbox.c
@@ -33,6 +33,7 @@ struct scmi_mailbox {
 	struct mbox_chan *chan_platform_receiver;
 	struct scmi_chan_info *cinfo;
 	struct scmi_shared_mem __iomem *shmem;
+	struct mutex chan_lock;
 };
 
 #define client_to_scmi_mailbox(c) container_of(c, struct scmi_mailbox, cl)
@@ -205,6 +206,7 @@ static int mailbox_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
 	cl->rx_callback = rx_callback;
 	cl->tx_block = false;
 	cl->knows_txdone = tx;
+	mutex_init(&smbox->chan_lock);
 
 	smbox->chan = mbox_request_channel(cl, tx ? 0 : p2a_chan);
 	if (IS_ERR(smbox->chan)) {
@@ -267,11 +269,21 @@ static int mailbox_send_message(struct scmi_chan_info *cinfo,
 	struct scmi_mailbox *smbox = cinfo->transport_info;
 	int ret;
 
+	/*
+	 * The mailbox layer has it's own queue. However the mailbox queue confuses
+	 * the per message SCMI timeouts since the clock starts when the message is
+	 * submitted into the mailbox queue. So when multiple messages are queued up
+	 * the clock starts on all messages instead of only the one inflight.
+	 */
+	mutex_lock(&smbox->chan_lock);
+
 	ret = mbox_send_message(smbox->chan, xfer);
 
 	/* mbox_send_message returns non-negative value on success, so reset */
 	if (ret > 0)
 		ret = 0;
+	else
+		mutex_unlock(&smbox->chan_lock);
 
 	return ret;
 }
@@ -281,13 +293,10 @@ static void mailbox_mark_txdone(struct scmi_chan_info *cinfo, int ret,
 {
 	struct scmi_mailbox *smbox = cinfo->transport_info;
 
-	/*
-	 * NOTE: we might prefer not to need the mailbox ticker to manage the
-	 * transfer queueing since the protocol layer queues things by itself.
-	 * Unfortunately, we have to kick the mailbox framework after we have
-	 * received our message.
-	 */
 	mbox_client_txdone(smbox->chan, ret);
+
+	/* Release channel */
+	mutex_unlock(&smbox->chan_lock);
 }
 
 static void mailbox_fetch_response(struct scmi_chan_info *cinfo,
-- 
2.34.1