[PATCH v2 3/3] soundwire: cadence: Drain the RX FIFO after an IO timeout

[Richard Fitzgerald]

If wait_for_completion_timeout() times-out in _cdns_xfer_msg() it
is possible that something could have been written to the RX FIFO.
In this case, we should drain the RX FIFO so that anything in it
doesn't carry over and mess up the next transfer.

Obviously, if we got to this state something went wrong, and we
don't really know the state of everything. The cleanup in this
situation cannot be bullet-proof but we should attempt to avoid
breaking future transaction, if only to reduce the amount of
error noise when debugging the failure from a kernel log.

Note that this patch only implements the draining for blocking
(non-deferred) transfers. The deferred API doesn't have any proper
handling of error conditions and would need some re-design before
implementing cleanup. That is a task for a separate patch...

Signed-off-by: Richard Fitzgerald <rf at opensource.cirrus.com>
---
Changes since v1:
The change is "the same" but the function that is moved up the
file has different content because of changes in patch #2
---
 drivers/soundwire/cadence_master.c | 50 ++++++++++++++++--------------
 1 file changed, 27 insertions(+), 23 deletions(-)

diff --git a/drivers/soundwire/cadence_master.c b/drivers/soundwire/cadence_master.c
index a6635f7f350e..521387322145 100644
--- a/drivers/soundwire/cadence_master.c
+++ b/drivers/soundwire/cadence_master.c
@@ -555,6 +555,29 @@ cdns_fill_msg_resp(struct sdw_cdns *cdns,
 	return SDW_CMD_OK;
 }
 
+static void cdns_read_response(struct sdw_cdns *cdns)
+{
+	u32 num_resp, cmd_base;
+	int i;
+
+	/* RX_FIFO_AVAIL can be 2 entries more than the FIFO size */
+	BUILD_BUG_ON(ARRAY_SIZE(cdns->response_buf) < CDNS_MCP_CMD_LEN + 2);
+
+	num_resp = cdns_readl(cdns, CDNS_MCP_FIFOSTAT);
+	num_resp &= CDNS_MCP_RX_FIFO_AVAIL;
+	if (num_resp > ARRAY_SIZE(cdns->response_buf)) {
+		dev_warn(cdns->dev, "RX AVAIL %d too long\n", num_resp);
+		num_resp = ARRAY_SIZE(cdns->response_buf);
+	}
+
+	cmd_base = CDNS_MCP_CMD_BASE;
+
+	for (i = 0; i < num_resp; i++) {
+		cdns->response_buf[i] = cdns_readl(cdns, cmd_base);
+		cmd_base += CDNS_MCP_CMD_WORD_LEN;
+	}
+}
+
 static enum sdw_command_response
 _cdns_xfer_msg(struct sdw_cdns *cdns, struct sdw_msg *msg, int cmd,
 	       int offset, int count, bool defer)
@@ -596,6 +619,10 @@ _cdns_xfer_msg(struct sdw_cdns *cdns, struct sdw_msg *msg, int cmd,
 		dev_err(cdns->dev, "IO transfer timed out, cmd %d device %d addr %x len %d\n",
 			cmd, msg->dev_num, msg->addr, msg->len);
 		msg->len = 0;
+
+		/* Drain anything in the RX_FIFO */
+		cdns_read_response(cdns);
+
 		return SDW_CMD_TIMEOUT;
 	}
 
@@ -769,29 +796,6 @@ EXPORT_SYMBOL(cdns_read_ping_status);
  * IRQ handling
  */
 
-static void cdns_read_response(struct sdw_cdns *cdns)
-{
-	u32 num_resp, cmd_base;
-	int i;
-
-	/* RX_FIFO_AVAIL can be 2 entries more than the FIFO size */
-	BUILD_BUG_ON(ARRAY_SIZE(cdns->response_buf) < CDNS_MCP_CMD_LEN + 2);
-
-	num_resp = cdns_readl(cdns, CDNS_MCP_FIFOSTAT);
-	num_resp &= CDNS_MCP_RX_FIFO_AVAIL;
-	if (num_resp > ARRAY_SIZE(cdns->response_buf)) {
-		dev_warn(cdns->dev, "RX AVAIL %d too long\n", num_resp);
-		num_resp = ARRAY_SIZE(cdns->response_buf);
-	}
-
-	cmd_base = CDNS_MCP_CMD_BASE;
-
-	for (i = 0; i < num_resp; i++) {
-		cdns->response_buf[i] = cdns_readl(cdns, cmd_base);
-		cmd_base += CDNS_MCP_CMD_WORD_LEN;
-	}
-}
-
 static int cdns_update_slave_status(struct sdw_cdns *cdns,
 				    u64 slave_intstat)
 {
-- 
2.30.2