Re: [Intel-gfx] [PATCH] drm/i915: Disable unused power wells left enabled by BIOS

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

On Wed, Feb 02, 2022 at 01:00:46PM +0200, Ville Syrjälä wrote:
> On Wed, Feb 02, 2022 at 12:42:49PM +0200, Imre Deak wrote:
> > Make sure all unused power wells left enabled by BIOS get disabled
> > during driver loading and system resume.
> > 
> > Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/5028
> > Signed-off-by: Imre Deak <imre.deak@intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_display.c  |  2 ++
> >  .../drm/i915/display/intel_display_power.c    | 31 +++++++++++++++++++
> >  .../drm/i915/display/intel_display_power.h    |  1 +
> >  3 files changed, 34 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> > index c431076f98a15..df347329d90e5 100644
> > --- a/drivers/gpu/drm/i915/display/intel_display.c
> > +++ b/drivers/gpu/drm/i915/display/intel_display.c
> > @@ -10664,6 +10664,8 @@ intel_modeset_setup_hw_state(struct drm_device *dev,
> >  	}
> >  
> >  	intel_display_power_put(dev_priv, POWER_DOMAIN_INIT, wakeref);
> > +
> > +	intel_power_domains_sanitize_state(dev_priv);
> 
> One slight concern is intel_vga_redisable() which is called after
> this during resume. Dunno if there's any way we could end up
> disabling the power well that houses the VGA logic before actually 
> turning off the VGA plane?

Yes, it could happen by the time
i915_drm_resume()->intel_display_resume() is called. Though, all the
power wells backing the VGA functionality are also in the INIT domain,
so would have caused a problem already before this patch.

i915_restore_display() also calls intel_vga_redisable(), so I think that
should handle the above scenario (and the second call can be removed as
you suggest below).

> Hmm. Maybe we should just reorder the intel_modeset_setup_hw_state()
> vs. intel_vga_redisable() anyway. We already do those in the opposite
> order during driver probe. No idea why we have a different order for
> resume.
> 
> Apart from that this seems sane enough to me.
> Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> >  }
> >  
> >  void intel_display_resume(struct drm_device *dev)
> > diff --git a/drivers/gpu/drm/i915/display/intel_display_power.c b/drivers/gpu/drm/i915/display/intel_display_power.c
> > index 369317805d245..d2102cc17bb4c 100644
> > --- a/drivers/gpu/drm/i915/display/intel_display_power.c
> > +++ b/drivers/gpu/drm/i915/display/intel_display_power.c
> > @@ -6213,6 +6213,37 @@ void intel_power_domains_driver_remove(struct drm_i915_private *i915)
> >  	intel_runtime_pm_put(&i915->runtime_pm, wakeref);
> >  }
> >  
> > +/**
> > + * intel_power_domains_sanitize_state - sanitize power domains state
> > + * @i915: i915 device instance
> > + *
> > + * Sanitize the power domains state during driver loading and system resume.
> > + * The function will disable all display power wells that BIOS has enabled
> > + * without a user for it (any user for a power well has taken a reference
> > + * on it by the time this function is called, after the state of all the
> > + * pipe, encoder, etc. HW resources have been sanitized).
> > + */
> > +void intel_power_domains_sanitize_state(struct drm_i915_private *i915)
> > +{
> > +	struct i915_power_domains *power_domains = &i915->power_domains;
> > +	struct i915_power_well *power_well;
> > +
> > +	mutex_lock(&power_domains->lock);
> > +
> > +	for_each_power_well_reverse(i915, power_well) {
> > +		if (power_well->desc->always_on || power_well->count ||
> > +		    !power_well->desc->ops->is_enabled(i915, power_well))
> > +			continue;
> > +
> > +		drm_dbg_kms(&i915->drm,
> > +			    "BIOS left unused %s power well enabled, disabling it\n",
> > +			    power_well->desc->name);
> > +		intel_power_well_disable(i915, power_well);
> > +	}
> > +
> > +	mutex_unlock(&power_domains->lock);
> > +}
> > +
> >  /**
> >   * intel_power_domains_enable - enable toggling of display power wells
> >   * @i915: i915 device instance
> > diff --git a/drivers/gpu/drm/i915/display/intel_display_power.h b/drivers/gpu/drm/i915/display/intel_display_power.h
> > index 686d18eaa24c8..a985f0e7ef78b 100644
> > --- a/drivers/gpu/drm/i915/display/intel_display_power.h
> > +++ b/drivers/gpu/drm/i915/display/intel_display_power.h
> > @@ -219,6 +219,7 @@ void intel_power_domains_disable(struct drm_i915_private *dev_priv);
> >  void intel_power_domains_suspend(struct drm_i915_private *dev_priv,
> >  				 enum i915_drm_suspend_mode);
> >  void intel_power_domains_resume(struct drm_i915_private *dev_priv);
> > +void intel_power_domains_sanitize_state(struct drm_i915_private *dev_priv);
> >  
> >  void intel_display_power_suspend_late(struct drm_i915_private *i915);
> >  void intel_display_power_resume_early(struct drm_i915_private *i915);
> > -- 
> > 2.27.0
> 
> -- 
> Ville Syrjälä
> Intel