Re: [Intel-gfx] [RFC] drm/i915/dp: PPS registers doesn't require AUX power

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

On Tue, Nov 24, 2020 at 03:28:47PM +0530, Anshuman Gupta wrote:
> Platforms with South Display Engine on PCH, doesn't
> require to get/put the AUX power domain in order to
> access PPS register because PPS registers are always on
> with South display on PCH.
> 
> Cc: Imre Deak <imre.deak@intel.com>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>

Could you describe the issue the patch is fixing?

For accessing PPS registers the AUX power well may not be needed, but
I'm not sure if this also applies to PPS functionality in general. For
instance forcing VDD is required for AUX functionality.

In any case we do need a power reference for any register access, so I
don't think not getting any power reference for PPS is ok.

--Imre

> ---
>  drivers/gpu/drm/i915/display/intel_dp.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 3896d08c4177..84a2c49e154c 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -872,8 +872,9 @@ 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)));
> +	if (!HAS_PCH_SPLIT(dev_priv))
> +		wakeref = intel_display_power_get(dev_priv,
> +						  intel_aux_power_domain(dp_to_dig_port(intel_dp)));
>  
>  	mutex_lock(&dev_priv->pps_mutex);
>  
> @@ -886,9 +887,11 @@ 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);
> +
> +	if (!HAS_PCH_SPLIT(dev_priv))
> +		intel_display_power_put(dev_priv,
> +					intel_aux_power_domain(dp_to_dig_port(intel_dp)),
> +					wakeref);
>  	return 0;
>  }
>  
> -- 
> 2.26.2
> 
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