linux-kernel - [PATCH] firmware: arm_scmi: fix timeout value for send

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Message-Id: <20200607193023.52344-1-jassisinghbrar@gmail.com>
Date:   Sun,  7 Jun 2020 14:30:23 -0500
From:   jassisinghbrar@...il.com
To:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     sudeep.holla@....com, viresh.kumar@...aro.org, robh@...nel.org,
        frowand.list@...il.com, bjorn.andersson@...aro.org,
        vincent.guittot@...aro.org, arnd@...db.de,
        Jassi Brar <jaswinder.singh@...aro.org>
Subject: [PATCH] firmware: arm_scmi: fix timeout value for send_message

From: Jassi Brar <jaswinder.singh@...aro.org>

Currently scmi_do_xfer() submits a message to mailbox api and waits
for an apparently very short time. This works if there are not many
messages in the queue already. However, if many clients share a
channel and/or each client submits many messages in a row, the
timeout value becomes too short and returns error even if the mailbox
is working fine according to the load. The timeout occurs when the
message is still in the api/queue awaiting its turn to ride the bus.

 Fix this by increasing the timeout value enough (500ms?) so that it
fails only if there is an actual problem in the transmission (like a
lockup or crash).

  [If we want to capture a situation when the remote didn't
respond within expected latency, then the timeout should not
start here, but from tx_prepare callback ... just before the
message physically gets on the channel]

Signed-off-by: Jassi Brar <jaswinder.singh@...aro.org>
---
 drivers/firmware/arm_scmi/driver.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
index dbec767222e9..46ddafe7ffc0 100644
--- a/drivers/firmware/arm_scmi/driver.c
+++ b/drivers/firmware/arm_scmi/driver.c
@@ -303,7 +303,7 @@ int scmi_do_xfer(const struct scmi_handle *handle, struct scmi_xfer *xfer)
 	}

 	if (xfer->hdr.poll_completion) {
-		ktime_t stop = ktime_add_ns(ktime_get(), SCMI_MAX_POLL_TO_NS);
+		ktime_t stop = ktime_add_ns(ktime_get(), 500 * 1000 * NSEC_PER_USEC);

 		spin_until_cond(scmi_xfer_done_no_timeout(cinfo, xfer, stop));

@@ -313,7 +313,7 @@ int scmi_do_xfer(const struct scmi_handle *handle, struct scmi_xfer *xfer)
 			ret = -ETIMEDOUT;
 	} else {
 		/* And we wait for the response. */
-		timeout = msecs_to_jiffies(info->desc->max_rx_timeout_ms);
+		timeout = msecs_to_jiffies(500);
 		if (!wait_for_completion_timeout(&xfer->done, timeout)) {
 			dev_err(dev, "timed out in resp(caller: %pS)\n",
 				(void *)_RET_IP_);
-- 
2.25.1