[PATCH v4 1/4] drm/i915: Fix false-positive assert_rpm_wakelock_held in i915_pmic_bus_access_notifier

[Hans de Goede]

Hi,

Note this v4 is send from my gmail in an attempt to keep the
X-Mailer: git-send-email header which the test-infra wants, but
that seems to have failed.

I've also just send another copy through my isp-s mail server,
but I've not received a copy of that copy myself ? If anyone
else has a second copy of this series can you please check if
the git-send-email header is there ?

If not can someone resend this series so that it can go through
the test infra ?

Regards,

Hans

On 20-08-17 14:51, Hans de Goede wrote:
> 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.
> 
> Reported-by: FKr <bugs-freedesktop at ubermail.me>
> Signed-off-by: Hans de Goede <hdegoede at redhat.com>
> Reviewed-by: Imre Deak <imre.deak at intel.com>
> ---
> Changes in v2:
> -Rebase on current (July 6th 2017) drm-next
> 
> Changes in v3:
> -Reword comment explaining why disabling the wakeref asserts is
>   ok and necessary
> -Add Imre's Reviewed-by
> ---
>   drivers/gpu/drm/i915/intel_uncore.c | 7 +++++++
>   1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> index 1d7b879cc68c..2d3aad319229 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.c
> +++ b/drivers/gpu/drm/i915/intel_uncore.c
> @@ -1171,8 +1171,15 @@ static int i915_pmic_bus_access_notifier(struct notifier_block *nb,
>   		 * 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);
>