linux-kernel - [PATCH v2 7/7] soc: microchip: mpfs: handle timeouts and failed services differently

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Date:   Fri, 20 Jan 2023 14:37:35 +0000
From:   Conor Dooley <conor.dooley@...rochip.com>
To:     Jassi Brar <jassisinghbrar@...il.com>
CC:     Conor Dooley <conor.dooley@...rochip.com>,
        Daire McNamara <daire.mcnamara@...rochip.com>,
        <linux-riscv@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH v2 7/7] soc: microchip: mpfs: handle timeouts and failed services differently

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@...rochip.com>
---
 drivers/soc/microchip/mpfs-sys-controller.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/drivers/soc/microchip/mpfs-sys-controller.c b/drivers/soc/microchip/mpfs-sys-controller.c
index da9cfeda6f78..2dd100ab21b1 100644
--- a/drivers/soc/microchip/mpfs-sys-controller.c
+++ b/drivers/soc/microchip/mpfs-sys-controller.c
@@ -45,14 +45,25 @@ 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;
+	}
 
 	ret = 0; /* mbox_send_message returns positive integers on success */
+
+	/*
+	 * 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.
+	 */
 	if (!wait_for_completion_timeout(&sys_controller->c, timeout)) {
-		ret = -ETIMEDOUT;
+		ret = -EBADMSG;
 		dev_warn(sys_controller->client.dev,
-			 "MPFS sys controller transaction timeout\n");
+			 "MPFS sys controller service failed\n");
 	}
 
 out:
@@ -110,6 +121,7 @@ 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)) {
-- 
2.39.0