Re: [PATCH 08/19] drm/i915/dp: Add a helper to decide if AS SDP can be used

["Nautiyal, Ankit K" <ankit.k.nautiyal@intel.com>]

On 3/30/2026 11:51 PM, Ville Syrjälä wrote:
> On Mon, Mar 30, 2026 at 09:36:45AM +0530, Ankit Nautiyal wrote:
>> Add a helper that determines whether AS SDP can be used for the
>> current DP configuration. For now this is true only when the sink
>> supports AS SDP and VRR is enabled, but more conditions may be added
>> later.
>>
>> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
>> ---
>>   drivers/gpu/drm/i915/display/intel_dp.c | 11 ++++++++++-
>>   1 file changed, 10 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
>> index 499850c2abcf..7ca3f9d583db 100644
>> --- a/drivers/gpu/drm/i915/display/intel_dp.c
>> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
>> @@ -3124,6 +3124,15 @@ static void intel_dp_compute_vsc_colorimetry(const struct intel_crtc_state *crtc
>>   	vsc->content_type = DP_CONTENT_TYPE_NOT_DEFINED;
>>   }
>>   
>> +static bool intel_dp_can_use_as_sdp(struct intel_dp *intel_dp,
>> +				    struct intel_crtc_state *crtc_state)
>> +{
>> +	if (!intel_dp->as_sdp_supported)
>> +		return false;
>> +
> Could have a FIXME here about fastset being borked with this. Didn't
> read far enough in the series yet to see if you did anything about that.

Hmm... let me check if I understand your concern correctly.

When VRR state changes through the fastset path, 
intel_dp_as_sdp_compute_config_late() will compute different AS SDP fields.

We do write the new values to the SDP DIP registers during update_pipe, 
but since AS SDP comparison is skipped during fastset,

we have no way to verify through state readback that the hardware 
actually latched the new values correctly.

Is that what you had in mind?

I'll add a FIXME about this.

Thanks,

Ankit


>
> Either way
> Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
>> +	return crtc_state->vrr.enable;
>> +}
>> +
>>   static void intel_dp_compute_as_sdp(struct intel_dp *intel_dp,
>>   				    struct intel_crtc_state *crtc_state)
>>   {
>> @@ -3131,7 +3140,7 @@ static void intel_dp_compute_as_sdp(struct intel_dp *intel_dp,
>>   	const struct drm_display_mode *adjusted_mode =
>>   		&crtc_state->hw.adjusted_mode;
>>   
>> -	if (!crtc_state->vrr.enable || !intel_dp->as_sdp_supported)
>> +	if (!intel_dp_can_use_as_sdp(intel_dp, crtc_state))
>>   		return;
>>   
>>   	crtc_state->infoframes.enable |= intel_hdmi_infoframe_enable(DP_SDP_ADAPTIVE_SYNC);
>> -- 
>> 2.45.2