[PATCH AUTOSEL 5.15 21/47] soundwire: cadence: Don't overwrite msg->buf during write commands

[Sasha Levin]

From: Richard Fitzgerald <rf at opensource.cirrus.com>

[ Upstream commit ba05b39d265bdd16913f7684600d9d41e2796745 ]

The buf passed in struct sdw_msg must only be written for a READ,
in that case the RDATA part of the response is the data value of the
register.

For a write command there is no RDATA, and buf should be assumed to
be const and unmodifable. The original caller should not expect its data
buffer to be corrupted by an sdw_nwrite().

Signed-off-by: Richard Fitzgerald <rf at opensource.cirrus.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>
Link: https://lore.kernel.org/r/20220916103505.1562210-1-rf@opensource.cirrus.com
Signed-off-by: Vinod Koul <vkoul at kernel.org>
Signed-off-by: Sasha Levin <sashal at kernel.org>
---
 drivers/soundwire/cadence_master.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/soundwire/cadence_master.c b/drivers/soundwire/cadence_master.c
index 4fcc3ba93004..18d2f9b3e201 100644
--- a/drivers/soundwire/cadence_master.c
+++ b/drivers/soundwire/cadence_master.c
@@ -545,9 +545,12 @@ cdns_fill_msg_resp(struct sdw_cdns *cdns,
 		return SDW_CMD_IGNORED;
 	}
 
-	/* fill response */
-	for (i = 0; i < count; i++)
-		msg->buf[i + offset] = FIELD_GET(CDNS_MCP_RESP_RDATA, cdns->response_buf[i]);
+	if (msg->flags == SDW_MSG_FLAG_READ) {
+		/* fill response */
+		for (i = 0; i < count; i++)
+			msg->buf[i + offset] = FIELD_GET(CDNS_MCP_RESP_RDATA,
+							 cdns->response_buf[i]);
+	}
 
 	return SDW_CMD_OK;
 }
-- 
2.35.1