[PATCH v3 8/8] soc: microchip: mpfs: handle timeouts and failed services differently

[Conor Dooley]

From: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>

The system controller will only deliver an interrupt if a service
succeeds. This leaves us in the unfortunate position with current code
where there is no way to differentiate between a legitimate timeout
where the service has not completed & where it has completed, but
failed.

mbox_send_message() has its own completion, and it will time out of the
system controller does not lower the busy flag. In this case, a timeout
has occurred and the error can be propagated back to the caller.

If the busy flag is lowered, but no interrupt has arrived to trigger the
rx callback, the service can be deemed to have failed. Report -EBADMSG
in this case so that callers can differentiate.

Signed-off-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
---
 drivers/soc/microchip/mpfs-sys-controller.c | 27 +++++++++++++++++----
 1 file changed, 22 insertions(+), 5 deletions(-)

diff --git a/drivers/soc/microchip/mpfs-sys-controller.c b/drivers/soc/microchip/mpfs-sys-controller.c
index e61ba9b7aae3..ceaeebc1fc6b 100644
--- a/drivers/soc/microchip/mpfs-sys-controller.c
+++ b/drivers/soc/microchip/mpfs-sys-controller.c
@@ -18,7 +18,11 @@
 #include <linux/platform_device.h>
 #include <soc/microchip/mpfs.h>
 
-#define MPFS_SYS_CTRL_TIMEOUT_MS 100
+/*
+ * This timeout must be long, as some services (example: image authentication)
+ * take significant time to complete
+ */
+#define MPFS_SYS_CTRL_TIMEOUT_MS 30000
 
 static DEFINE_MUTEX(transaction_lock);
 
@@ -41,14 +45,26 @@ int mpfs_blocking_transaction(struct mpfs_sys_controller *sys_controller, struct
 	reinit_completion(&sys_controller->c);
 
 	ret = mbox_send_message(sys_controller->chan, msg);
-	if (ret < 0)
+	if (ret < 0) {
+		dev_warn(sys_controller->client.dev, "MPFS sys controller service timeout\n");
 		goto out;
+	}
 
+	/*
+	 * Unfortunately, the system controller will only deliver an interrupt
+	 * if a service succeeds. mbox_send_message() will block until the busy
+	 * flag is gone. If the busy flag is gone but no interrupt has arrived
+	 * to trigger the rx callback then the service can be deemed to have
+	 * failed.
+	 * The caller can then interrogate msg::response::resp_status to
+	 * determine the cause of the failure.
+	 * mbox_send_message() returns positive integers in the success path, so
+	 * ret needs to be cleared if we do get an interrupt.
+	 */
 	if (!wait_for_completion_timeout(&sys_controller->c, timeout)) {
-		ret = -ETIMEDOUT;
-		dev_warn(sys_controller->client.dev, "MPFS sys controller transaction timeout\n");
+		ret = -EBADMSG;
+		dev_warn(sys_controller->client.dev, "MPFS sys controller service failed\n");
 	} else {
-		/* mbox_send_message() returns positive integers on success */
 		ret = 0;
 	}
 
@@ -107,6 +123,7 @@ static int mpfs_sys_controller_probe(struct platform_device *pdev)
 	sys_controller->client.dev = dev;
 	sys_controller->client.rx_callback = rx_callback;
 	sys_controller->client.tx_block = 1U;
+	sys_controller->client.tx_tout = msecs_to_jiffies(MPFS_SYS_CTRL_TIMEOUT_MS);
 
 	sys_controller->chan = mbox_request_channel(&sys_controller->client, 0);
 	if (IS_ERR(sys_controller->chan)) {
-- 
2.39.2