Re: [PATCH] drm/xe/pm: Change HPD to polling on runtime suspend

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

On Wed, Aug 07, 2024 at 12:15:33PM +0300, Murthy, Arun R wrote:
> 
> > -----Original Message-----
> > From: Deak, Imre <imre.deak@intel.com>
> > Sent: Tuesday, August 6, 2024 10:11 PM
> > To: Murthy, Arun R <arun.r.murthy@intel.com>
> > Cc: intel-xe@lists.freedesktop.org; intel-gfx@lists.freedesktop.org
> > Subject: Re: [PATCH] drm/xe/pm: Change HPD to polling on runtime suspend
> >
> > On Tue, Aug 06, 2024 at 02:25:13PM +0530, Arun R Murthy wrote:
> > > HPD is interrupt based and on runtime suspend change it to polling as
> > > HPD is not a wakeup event. A worker thread is scheduled for doing this
> > > polling and it keeps polling for HPD live status on an internval of 10s.
> > > On runtime resume disable polling and fallback to interrupt mechanism.
> > >
> > > Signed-off-by: Arun R Murthy <arun.r.murthy@intel.com>
> > > ---
> > >  drivers/gpu/drm/xe/xe_pm.c | 6 ++++++
> > >  1 file changed, 6 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/xe/xe_pm.c b/drivers/gpu/drm/xe/xe_pm.c
> > > index 9f3c14fd9f33..d952b06ebfb4 100644
> > > --- a/drivers/gpu/drm/xe/xe_pm.c
> > > +++ b/drivers/gpu/drm/xe/xe_pm.c
> > > @@ -22,6 +22,7 @@
> > >  #include "xe_pcode.h"
> > >  #include "xe_trace.h"
> > >  #include "xe_wa.h"
> > > +#include "intel_hotplug.h"
> > >
> > >  /**
> > >   * DOC: Xe Power Management
> > > @@ -378,6 +379,8 @@ int xe_pm_runtime_suspend(struct xe_device *xe)
> > >             if (err)
> > >                     goto out;
> > >     }
> > > +   /* Enable hpd polling on runtime suspend */
> > > +   intel_hpd_poll_enable(xe);
> > >
> > >     xe_irq_suspend(xe);
> > >
> > > @@ -427,6 +430,9 @@ int xe_pm_runtime_resume(struct xe_device *xe)
> > >
> > >     xe_irq_resume(xe);
> > >
> > > +   /* Disable hpd polling on runtime resume */
> > > +   intel_hpd_poll_disable(xe);
> >
> > This should be handled in xe_display_pm_resume() (likewise enabling polling in
> > xe_display_pm_suspend()), in fact it's already called there.
>
> In xe_display_pm_suspend we have drm_kms_helper_poll_disable and it disables
> output polling.

What I meant is that intel_hpd_poll_disable() is already called in
xe_display_pm_resume(), which you would call now twice during runtime
resume if d3cold is allowed.

drm_kms_helper_poll_disable() in xe_display_pm_suspend() should be
called only during system suspend, which is another thing to fix there.

> Moreover we don't have the functions defined for enable/disable_hpd
> defined in connector_ops which is referenced by
> drm_kms_helper_poll_enable/disable.
> 
> What we need is on runtime_suspend the poll work should be
> enabled so that hotplug can be detected and can come out of runtime_suspend.
> The same poll work is not required on system suspend.

All the display related suspend/resume handling is done already in
xe_display_pm_suspend()/resume() or in xe_display.c in general, both for
runtime and system suspend/resume. The reason for that is to keep the
display specific parts separate from the generic/higher-level device
suspend/resume handling in xe_pm.c. New display specific things added
should keep this separation.

> > Also this is missing the xe->info.enable_display check and polling shouldn't be
> > enabled when system (vs. runtime) suspending.
> Probably HAS_DISPLAY can be added before calling this intel_hpd_poll_enable.
> 
> Thanks and Regards,
> Arun R Murthy
> --------------------
> >
> > Not sure why the display is suspended/resumed only if d3cold is allowed, for
> > many of the display s/r steps at least it doesn't make sense to me.
> > For now moving the d3cold check within
> > xe_display_pm_suspend()/resume() and enabling/disabling polling regardless of
> > that flag would be the simplest imo.
> >
> > > +
> > >     for_each_gt(gt, xe, id)
> > >             xe_gt_resume(gt);
> > >
> > > --
> > > 2.25.1
> > >