[PATCH] soundwire: bus: add dev_warn() messages to track UNATTACHED devices

[Bard Liao <yung-chuan.liao@linux.intel.com>]

From: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>

In rare cases, some devices seem to lose sync and never re-attach on
the bus. This seems to happen only when there are more than one device
per link, which suggests either an electrical issue, a race condition
or a state machine issue.

Add two dev_warn() messages to identify the sequence by which the
devices become UNATTACHED.

BugLink: https://github.com/thesofproject/linux/issues/3063
BugLink: https://github.com/thesofproject/linux/issues/3325
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Rander Wang <rander.wang@intel.com>
Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
---
 drivers/soundwire/bus.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/soundwire/bus.c b/drivers/soundwire/bus.c
index 67369e941d0d..354d3f89366f 100644
--- a/drivers/soundwire/bus.c
+++ b/drivers/soundwire/bus.c
@@ -1749,8 +1749,11 @@ int sdw_handle_slave_status(struct sdw_bus *bus,
 			continue;
 
 		if (status[i] == SDW_SLAVE_UNATTACHED &&
-		    slave->status != SDW_SLAVE_UNATTACHED)
+		    slave->status != SDW_SLAVE_UNATTACHED) {
+			dev_warn(&slave->dev, "Slave %d state check1: UNATTACHED, status was %d\n",
+				 i, slave->status);
 			sdw_modify_slave_status(slave, SDW_SLAVE_UNATTACHED);
+		}
 	}
 
 	if (status[0] == SDW_SLAVE_ATTACHED) {
@@ -1785,6 +1788,9 @@ int sdw_handle_slave_status(struct sdw_bus *bus,
 			if (slave->status == SDW_SLAVE_UNATTACHED)
 				break;
 
+			dev_warn(&slave->dev, "Slave %d state check2: UNATTACHED, status was %d\n",
+				 i, slave->status);
+
 			sdw_modify_slave_status(slave, SDW_SLAVE_UNATTACHED);
 			break;
 
-- 
2.17.1