Patch "drm/i915: Fix false-positive assert_rpm_wakelock_held in i915_pmic_bus_access_notifier v2" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

drm/i915: Fix false-positive assert_rpm_wakelock_held in i915_pmic_bus_access_notifier v2

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
drm-i915-fix-false-positive-assert_rpm_wakelock_held-in-i915_pmic_bus_access_notifier-v2.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Hans de Goede <[email protected]>
Date: Fri, 10 Nov 2017 16:03:01 +0100
Subject: drm/i915: Fix false-positive assert_rpm_wakelock_held in i915_pmic_bus_access_notifier v2

From: Hans de Goede <[email protected]>

commit f4359cedfb43b934f38c50d1604db21333abe57b upstream.

assert_rpm_wakelock_held is triggered from i915_pmic_bus_access_notifier even though it gets unregistered on (runtime) suspend, this is caused by a race happening under the following circumstances:

intel_runtime_pm_put does:

   atomic_dec(&dev_priv->pm.wakeref_count);

   pm_runtime_mark_last_busy(kdev);
   pm_runtime_put_autosuspend(kdev);

And pm_runtime_put_autosuspend calls intel_runtime_suspend from a workqueue, so there is ample of time between the atomic_dec() and intel_runtime_suspend() unregistering the notifier. If the notifier gets called in this windowd assert_rpm_wakelock_held falsely triggers (at this point we're not runtime-suspended yet).

This commit adds disable_rpm_wakeref_asserts and enable_rpm_wakeref_asserts calls around the intel_uncore_forcewake_get(FORCEWAKE_ALL) call in i915_pmic_bus_access_notifier fixing the false-positive WARN_ON.

Changes in v2:
-Reword comment explaining why disabling the wakeref asserts is
ok and necessary

---
 drivers/gpu/drm/i915/intel_uncore.c |    7 +++++++
 1 file changed, 7 insertions(+)

@@ -1171,8 +1171,15 @@ static int i915_pmic_bus_access_notifier
 		 * bus, which will be busy after this notification, leading to:
 		 * "render: timed out waiting for forcewake ack request."
 		 * errors.
+		 *
+		 * The notifier is unregistered during intel_runtime_suspend(),
+		 * so it's ok to access the HW here without holding a RPM
+		 * wake reference -> disable wakeref asserts for the time of
+		 * the access.
 		 */
+		disable_rpm_wakeref_asserts(dev_priv);
 		intel_uncore_forcewake_get(dev_priv, FORCEWAKE_ALL);
+		enable_rpm_wakeref_asserts(dev_priv);
 		break;
 	case MBI_PMIC_BUS_ACCESS_END:
 		intel_uncore_forcewake_put(dev_priv, FORCEWAKE_ALL);

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/drm-i915-re-register-pmic-bus-access-notifier-on-runtime-resume.patch queue-4.14/drm-i915-fix-false-positive-assert_rpm_wakelock_held-in-i915_pmic_bus_access_notifier-v2.patch