[PATCH 3/3] soundwire: bus: pm_runtime_request_resume on peripheral attachment

[Bard Liao]

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

In typical use cases, the peripheral becomes pm_runtime active as a
result of the ALSA/ASoC framework starting up a DAI. The parent/child
hierarchy guarantees that the manager device will be fully resumed
beforehand.

There is however a corner case where the manager device may become
pm_runtime active, but without ALSA/ASoC requesting any functionality
from the peripherals. In this case, the hardware peripheral device
will report as ATTACHED and its initialization routine will be
executed. If this initialization routine initiates any sort of
deferred processing, there is a possibility that the manager could
suspend without the peripheral suspend sequence being invoked: from
the pm_runtime framework perspective, the peripheral is *already*
suspended.

To avoid such disconnects between hardware state and pm_runtime state,
this patch adds an asynchronous pm_request_resume() upon successful
attach/initialization which will result in the proper resume/suspend
sequence to be followed on the peripheral side.

BugLink: https://github.com/thesofproject/linux/issues/3459
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan at linux.intel.com>
Reviewed-by: Rander Wang <rander.wang at intel.com>
Signed-off-by: Bard Liao <yung-chuan.liao at linux.intel.com>
---
 drivers/soundwire/bus.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/soundwire/bus.c b/drivers/soundwire/bus.c
index 354d3f89366f..8b7a680f388e 100644
--- a/drivers/soundwire/bus.c
+++ b/drivers/soundwire/bus.c
@@ -1838,6 +1838,18 @@ int sdw_handle_slave_status(struct sdw_bus *bus,
 				__func__, slave->dev_num);
 
 			complete(&slave->initialization_complete);
+
+			/*
+			 * If the manager became pm_runtime active, the peripherals will be
+			 * restarted and attach, but their pm_runtime status may remain
+			 * suspended. If the 'update_slave_status' callback initiates
+			 * any sort of deferred processing, this processing would not be
+			 * cancelled on pm_runtime suspend.
+			 * To avoid such zombie states, we queue a request to resume.
+			 * This would be a no-op in case the peripheral was being resumed
+			 * by e.g. the ALSA/ASoC framework.
+			 */
+			pm_request_resume(&slave->dev);
 		}
 	}
 
-- 
2.17.1