Re: [PATCH v2] drm/i915: Disable DRRS when PSR is enabled

[Jani Nikula <jani.nikula@intel.com>]

On Sat, 09 Sep 2017, "Pandiyan, Dhinakaran" <dhinakaran.pandiyan@intel.com> wrote:
> On Thu, 2017-08-31 at 14:17 -0700, Radhakrishna Sripada wrote:
>> Some platforms donot support PSR and DRRS simultaneously.
>
> I could not verify which platforms support PSR + DRRS and which don't.
> But, seems safe to have DRRS disabled for all platforms when PSR is
> enabled.
>
>
>
>> Visual artifacts and flickering were reported on BDW HP Spectre
>> x360 Convertible. Deferring to PSR when both PSR and DRRS are
>> supported by the panel.
>> 
>> V2: Minor code-style changes suggested by Rodrigo
>> 
>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=101111
>> Cc: Nicholas Stommel <nicholas.stommel@gmail.com>
>> Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
>> Cc: Jani Nikula <jani.nikula@intel.com>
>> Cc: Clinton Taylor <clinton.a.taylor@intel.com>
>> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
>> Signed-off-by: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
>> ---
>>  drivers/gpu/drm/i915/intel_dp.c | 10 +++++-----
>>  1 file changed, 5 insertions(+), 5 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
>> index 887953c0f495..aa5a69301257 100644
>> --- a/drivers/gpu/drm/i915/intel_dp.c
>> +++ b/drivers/gpu/drm/i915/intel_dp.c
>> @@ -5467,11 +5467,6 @@ static void intel_dp_set_drrs_state(struct drm_i915_private *dev_priv,
>>  		return;
>>  	}
>>  
>> -	/*
>> -	 * FIXME: This needs proper synchronization with psr state for some
>> -	 * platforms that cannot have PSR and DRRS enabled at the same time.
>> -	 */
>> -
>>  	dig_port = dp_to_dig_port(intel_dp);
>>  	encoder = &dig_port->base;
>>  	intel_crtc = to_intel_crtc(encoder->base.crtc);
>> @@ -5555,6 +5550,11 @@ void intel_edp_drrs_enable(struct intel_dp *intel_dp,
>>  		return;
>>  	}
>>  
>> +	if (dev_priv->psr.enabled) {
>> +		DRM_DEBUG_KMS("PSR enabled. Disabling DRRS.\n");
>> +		return;
>> +	}
>
> So every time a flush/invalidate happens, we end up taking the
> drrs.mutex and then returning because dev_priv->drrs.dp is NULL. That
> seems unnecessary. Have your considered drrs.type = DRRS_NOT_SUPPORTED?

That would prevent DRRS testing by disabling PSR via module parameter. I
think this is fine. Although the debug message is misleading; it's "not
enabling DRRS", not "disabling DRRS". There's a difference.

Side note, dev_priv->drrs.type is redundant and could be replaced with
direct use of dev_priv->vbt.drrs_type.

> And this solution relies on the ordering that psr_enable() is done
> before drrs_enable(), we need a comment in enable_ddi to make a note of
> that. A WARN_ON in psr_enable() if drrs is already enabled might work
> too.

I think a WARN_ON would be fine.

BR,
Jani.

>
>
>> +
>>  	mutex_lock(&dev_priv->drrs.mutex);
>>  	if (WARN_ON(dev_priv->drrs.dp)) {
>>  		DRM_ERROR("DRRS already enabled\n");

-- 
Jani Nikula, Intel Open Source Technology Center
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