linux-kernel - [PATCH 1/2] fsi: scom: Fix error handling

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Date:   Tue,  7 Dec 2021 14:08:10 +1030
From:   Joel Stanley <joel@....id.au>
To:     Jeremy Kerr <jk@...abs.org>,
        Alistar Popple <alistair@...ple.id.au>,
        Eddie James <eajames@...ux.ibm.com>
Cc:     linux-fsi@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Greg KH <gregkh@...uxfoundation.org>
Subject: [PATCH 1/2] fsi: scom: Fix error handling

SCOM error handling is made complex by trying to pass around two bits of
information: the function return code, and a status parameter that
represents the CFAM error status register.

The commit f72ddbe1d7b7 ("fsi: scom: Remove retries") removed the
"hidden" retries in the SCOM driver, in preference of allowing the
calling code (userspace or driver) to decide how to handle a failed
SCOM. However it introduced a bug by attempting to be smart about the
return codes that were "errors" and which were ok to fall through to the
status register parsing.

We get the following errors:

 - EINVAL or ENXIO, for indirect scoms where the value is invalid
 - EINVAL, where the size or address is incorrect
 - EIO or ETIMEOUT, where FSI write failed (aspeed master)
 - EAGAIN, where the master detected a crc error (GPIO master only)
 - EBUSY, where the bus is disabled (GPIO master in external mode)

In all of these cases we should fail the SCOM read/write and return the
error.

Thanks to Dan Carpenter for the detailed bug report.

Fixes: f72ddbe1d7b7 ("fsi: scom: Remove retries")
Link: https://lists.ozlabs.org/pipermail/linux-fsi/2021-November/000235.html
Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
Signed-off-by: Joel Stanley <joel@....id.au>
---
 drivers/fsi/fsi-scom.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/fsi/fsi-scom.c b/drivers/fsi/fsi-scom.c
index da1486bb6a14..3b427f7e9027 100644
--- a/drivers/fsi/fsi-scom.c
+++ b/drivers/fsi/fsi-scom.c
@@ -289,7 +289,7 @@ static int put_scom(struct scom_device *scom, uint64_t value,
 	int rc;
 
 	rc = raw_put_scom(scom, value, addr, &status);
-	if (rc == -ENODEV)
+	if (rc)
 		return rc;
 
 	rc = handle_fsi2pib_status(scom, status);
@@ -308,7 +308,7 @@ static int get_scom(struct scom_device *scom, uint64_t *value,
 	int rc;
 
 	rc = raw_get_scom(scom, value, addr, &status);
-	if (rc == -ENODEV)
+	if (rc)
 		return rc;
 
 	rc = handle_fsi2pib_status(scom, status);
-- 
2.33.0