[Intel-gfx] [PATCH 1/2] drm/i915: Schedule the HPD poll init work on an unbound workqueue

[Lucas De Marchi]

+Jani

On Fri, Sep 01, 2023 at 05:04:02PM +0300, Imre Deak wrote:
>Disabling HPD polling from i915_hpd_poll_init_work() involves probing
>all display connectors explicitly to account for lost hotplug
>interrupts. On some platforms (mostly pre-ICL) with HDMI connectors the
>I2C EDID bit-banging using udelay() triggers in turn the
>
> workqueue: i915_hpd_poll_init_work [i915] hogged CPU for >10000us 4 times, consider switching to WQ_UNBOUND
>
>warning.
>
>Fix the above by scheduling i915_hpd_poll_init_work() on a WQ_UNBOUND
>workqueue. It's ok to use a system WQ, since i915_hpd_poll_init_work()
>is properly flushed in intel_hpd_cancel_work().
>
>The connector probing from drm_mode_config::output_poll_work resulting
>in the same warning is fixed by the next patch.
>
>Cc: Tejun Heo <tj at kernel.org>
>Cc: Heiner Kallweit <hkallweit1 at gmail.com>
>CC: stable at vger.kernel.org # 6.5
>Suggested-by: Tejun Heo <tj at kernel.org>
>Suggested-by: Heiner Kallweit <hkallweit1 at gmail.com>
>Reported-by: Heiner Kallweit <hkallweit1 at 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 at intel.com>
>---
> drivers/gpu/drm/i915/display/intel_hotplug.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
>diff --git a/drivers/gpu/drm/i915/display/intel_hotplug.c b/drivers/gpu/drm/i915/display/intel_hotplug.c
>index e8562f6f8bb44..accc2fec562a0 100644
>--- a/drivers/gpu/drm/i915/display/intel_hotplug.c
>+++ b/drivers/gpu/drm/i915/display/intel_hotplug.c
>@@ -774,7 +774,7 @@ void intel_hpd_poll_enable(struct drm_i915_private *dev_priv)
> 	 * As well, there's no issue if we race here since we always reschedule
> 	 * this worker anyway
> 	 */
>-	queue_work(dev_priv->unordered_wq,
>+	queue_work(system_unbound_wq,
> 		   &dev_priv->display.hotplug.poll_init_work);
> }
>
>@@ -803,7 +803,7 @@ void intel_hpd_poll_disable(struct drm_i915_private *dev_priv)
> 		return;
>
> 	WRITE_ONCE(dev_priv->display.hotplug.poll_enabled, false);
>-	queue_work(dev_priv->unordered_wq,
>+	queue_work(system_unbound_wq,

This 1y+ patch doesn't apply anymore and now we also have xe to account
for.  I'm reviving this since we are unifying the kernel config in CI
and now several machines testing i915 start to hit this warning.

Looking at the current code for xe we have:

	drivers/gpu/drm/xe/xe_device_types.h:

         /** @unordered_wq: used to serialize unordered work, mostly display */
         struct workqueue_struct *unordered_wq;


... which is, actually, just display.

Jani, should we move this wq to display where it belongs, with the right
flags, rather than queueing it on system_unbound_wq?

Lucas De Marchi

> 		   &dev_priv->display.hotplug.poll_init_work);
> }
>
>-- 
>2.37.2
>