[PATCH 2/2] drm: Schedule the HPD poll work on the system unbound workqueue

[Imre Deak <imre.deak@intel.com>]

On some i915 platforms at least the HPD poll work involves I2C
bit-banging using udelay()s to probe for monitor EDIDs. This in turn
may trigger the

 workqueue: output_poll_execute [drm_kms_helper] hogged CPU for >10000us 4 times, consider switching to WQ_UNBOUND

warning. Fix this by scheduling drm_mode_config::output_poll_work on a
WQ_UNBOUND workqueue.

Cc: Tejun Heo <tj@kernel.org>
Cc: Heiner Kallweit <hkallweit1@gmail.com>
CC: stable@vger.kernel.org # 6.5
Cc: dri-devel@lists.freedesktop.org
Suggested-by: Tejun Heo <tj@kernel.org>
Suggested-by: Heiner Kallweit <hkallweit1@gmail.com>
Reported-by: Heiner Kallweit <hkallweit1@gmail.com>
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/9245
Link: https://lore.kernel.org/all/f7e21caa-e98d-e5b5-932a-fe12d27fde9b@gmail.com
Signed-off-by: Imre Deak <imre.deak@intel.com>
---
 drivers/gpu/drm/drm_probe_helper.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
index 3f479483d7d80..72eac0cd25e74 100644
--- a/drivers/gpu/drm/drm_probe_helper.c
+++ b/drivers/gpu/drm/drm_probe_helper.c
@@ -279,7 +279,8 @@ static void reschedule_output_poll_work(struct drm_device *dev)
 		 */
 		delay = HZ;
 
-	schedule_delayed_work(&dev->mode_config.output_poll_work, delay);
+	queue_delayed_work(system_unbound_wq,
+			   &dev->mode_config.output_poll_work, delay);
 }
 
 /**
@@ -614,7 +615,7 @@ int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
 		 */
 		dev->mode_config.delayed_event = true;
 		if (dev->mode_config.poll_enabled)
-			mod_delayed_work(system_wq,
+			mod_delayed_work(system_unbound_wq,
 					 &dev->mode_config.output_poll_work,
 					 0);
 	}
@@ -838,7 +839,8 @@ static void output_poll_execute(struct work_struct *work)
 		drm_kms_helper_hotplug_event(dev);
 
 	if (repoll)
-		schedule_delayed_work(delayed_work, DRM_OUTPUT_POLL_PERIOD);
+		queue_delayed_work(system_unbound_wq,
+				   delayed_work, DRM_OUTPUT_POLL_PERIOD);
 }
 
 /**
-- 
2.37.2