[Intel-gfx] [PATCH] drm/i915/pps: Reuse POWER_DOMAIN_DISPLAY_CORE in pps_{lock, unlock}

[Jani Nikula]

On Fri, 08 Jan 2021, Imre Deak <imre.deak at intel.com> wrote:
> On Fri, Jan 08, 2021 at 11:38:04AM +0200, Jani Nikula wrote:
>> On Thu, 07 Jan 2021, Anshuman Gupta <anshuman.gupta at intel.com> wrote:
>> > We need a power_domain wakeref in pps_{lock,unlock} to prevent
>> > a race while resetting pps state in intel_power_sequencer_reset().
>> >
>> > intel_power_sequencer_reset() need a pps_mutex to access pps_pipe
>> > but it can't grab pps_mutex due to deadlock with power_well
>> > functions are called while holding pps_mutex.
>> > intel_power_sequencer_reset() is called by power_well function
>> > associated with legacy platforms like vlv and chv therefore re-use
>> > the POWER_DOMAIN_DISPLAY_CORE power domain, which only used
>> > by vlv and chv display power domain.
>> >
>> > This will avoids the unnecessary noise of unrelated power wells
>> > in pps_{lock,unlock}.
>> >
>> > Cc: Jani Nikula <jani.nikula at intel.com>
>> > Cc: Imre Deak <imre.deak at intel.com>
>> > Signed-off-by: Anshuman Gupta <anshuman.gupta at intel.com>
>> 
>> Imre convinced me yesterday on irc that this should work.
>> 
>> Reviewed-by: Jani Nikula <jani.nikula at intel.com>
>> 
>> On the surface, this reduces the need to enable/disable the aux power so
>> much. It's unnecessary, so it stands to reason to optimize it. We should
>> only grab the domain references we actually need.
>> 
>> However, this *also* papers over an issue we've been seeing [1]. We need
>> to be aware the root cause for that remains unknown, and needs to be
>> figured out.
>> 
>> I presume simply doing aux transfers won't reproduce the problem,
>> because that disables the power asynchronously since commit f39194a7a8b9
>> ("drm/i915: Disable power asynchronously during DP AUX
>> transfers"). Perhaps we wouldn't have seen this at all if pps_unlock()
>> also did that as suggested in the commit message.
>> 
>> Anyway, I'd like to get acks or rb's from Imre and Ville before merging
>> this.
>
> Looks ok to me:
> Acked-by: Imre Deak <imre.deak at intel.com>

Thanks, pushed to din.

BR,
Jani.


>
>> 
>> 
>> BR,
>> Jani.
>> 
>> 
>> [1] http://lore.kernel.org/r/20201204081845.26528-1-anshuman.gupta@intel.com
>> 
>> 
>> > ---
>> >  drivers/gpu/drm/i915/display/intel_dp.c | 8 ++------
>> >  1 file changed, 2 insertions(+), 6 deletions(-)
>> >
>> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
>> > index 8a00e609085f..4f190a82d4ad 100644
>> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
>> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
>> > @@ -895,9 +895,7 @@ pps_lock(struct intel_dp *intel_dp)
>> >  	 * See intel_power_sequencer_reset() why we need
>> >  	 * a power domain reference here.
>> >  	 */
>> > -	wakeref = intel_display_power_get(dev_priv,
>> > -					  intel_aux_power_domain(dp_to_dig_port(intel_dp)));
>> > -
>> > +	wakeref = intel_display_power_get(dev_priv, POWER_DOMAIN_DISPLAY_CORE);
>> >  	mutex_lock(&dev_priv->pps_mutex);
>> >  
>> >  	return wakeref;
>> > @@ -909,9 +907,7 @@ pps_unlock(struct intel_dp *intel_dp, intel_wakeref_t wakeref)
>> >  	struct drm_i915_private *dev_priv = dp_to_i915(intel_dp);
>> >  
>> >  	mutex_unlock(&dev_priv->pps_mutex);
>> > -	intel_display_power_put(dev_priv,
>> > -				intel_aux_power_domain(dp_to_dig_port(intel_dp)),
>> > -				wakeref);
>> > +	intel_display_power_put(dev_priv, POWER_DOMAIN_DISPLAY_CORE, wakeref);
>> >  	return 0;
>> >  }
>> 
>> -- 
>> Jani Nikula, Intel Open Source Graphics Center
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-- 
Jani Nikula, Intel Open Source Graphics Center