Re: [PATCH 12/19] drm/i915/dp: Add member to intel_dp to store AS SDP v2 support

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

On 3/30/2026 11:59 PM, Ville Syrjälä wrote:
> On Mon, Mar 30, 2026 at 09:36:49AM +0530, Ankit Nautiyal wrote:
>> DP v2.1 SCR advertises support for FAVT payload fields parsing in DPCD
>> 0x2214 Bit 2. This indicates the support for Adaptive-Sync SDP version 2
>> (AS SDP v2), which allows the source to set the version in HB2[4:0] and the
>> payload length in HB3[5:0] of the AS SDP header.
>>
>> DP v2.1 SCR also adds a bit for Async Video Timing during Panel Replay, in
>> Panel Replay Capability DPCD 0x00b1 (Bit 3). When this bit is cleared, the
>> sink supports asynchronous video timing while in a Panel Replay Active
>> state. The spec mandates that such sinks shall support AS SDP v2.
>>
>> Infer AS SDP v2 support from these capabilities and store it in
>> struct intel_dp for use by subsequent feature enablement changes.
>>
>> v2:
>>   - Include parsing ASYNC_VIDEO_TIMING_NOT_SUPPORTED_IN_PR bit to
>>     determine AS SDP v2 support. (Ville)
>>
>> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
>> ---
>>   .../drm/i915/display/intel_display_types.h    |  1 +
>>   drivers/gpu/drm/i915/display/intel_dp.c       | 37 +++++++++++++++++++
>>   2 files changed, 38 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
>> index e2496db1642a..efc609eef4f5 100644
>> --- a/drivers/gpu/drm/i915/display/intel_display_types.h
>> +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
>> @@ -1870,6 +1870,7 @@ struct intel_dp {
>>   	/* connector directly attached - won't be use for modeset in mst world */
>>   	struct intel_connector *attached_connector;
>>   	bool as_sdp_supported;
>> +	bool as_sdp_v2_supported;
>>   
>>   	struct drm_dp_tunnel *tunnel;
>>   	bool tunnel_suspended:1;
>> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
>> index f9bfb07f0205..b2007ffe18bc 100644
>> --- a/drivers/gpu/drm/i915/display/intel_dp.c
>> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
>> @@ -6301,6 +6301,40 @@ intel_dp_unset_edid(struct intel_dp *intel_dp)
>>   					       false);
>>   }
>>   
>> +static bool
>> +intel_dp_sink_supports_as_sdp_v2(struct intel_dp *intel_dp)
>> +{
>> +	u8 rx_features;
>> +	u8 pr_caps;
>> +
>> +	/*
>> +	 * The DP spec does not explicitly provide the AS SDP v2 capability.
>> +	 * So based on the DP v2.1 SCR, we infer it from the following bits:
>> +	 *
>> +	 * DP_AS_SDP_FAVT_PAYLOAD_FIELDS_PARSING_SUPPORTED indicates support for
>> +	 * FAVT, which is explicitly defined to use AS SDP v2.
>> +	 *
>> +	 * DP_ASYNC_VIDEO_TIMING_NOT_SUPPORTED_IN_PR cleared indicates support
>> +	 * for Async Video timing in PR active and the spec mandates that such
>> +	 * sinks shall support AS SDP v2.
>> +	 */
>> +	if (drm_dp_dpcd_read_byte(&intel_dp->aux,
>> +				  DP_DPRX_FEATURE_ENUMERATION_LIST_CONT_1,
>> +				  &rx_features) == 1) {
>> +		if (rx_features & DP_AS_SDP_FAVT_PAYLOAD_FIELDS_PARSING_SUPPORTED)
>> +			return true;
>> +	}
>> +
>> +	if (drm_dp_dpcd_read_byte(&intel_dp->aux,
>> +				  DP_PANEL_REPLAY_CAP_CAPABILITY,
>> +				  &pr_caps) == 1) {
>> +		if (!(pr_caps & DP_PANEL_REPLAY_ASYNC_VIDEO_TIMING_NOT_SUPPORTED_IN_PR))
> That seems to be backwards. If the sink requires AS SDP
> then it will set the bit.


Hmm.. I indeed got it backwards, you are right.

If Async Video timing is supported then re-set the bit. But in that case 
AS SDP is not required.

So reset means AS SDP not required; bit set means it is required.

Thanks, I will correct this in next version.

Regards,

Ankit

>
>> +			return true;
>> +	}
>> +
>> +	return false;
>> +}
>> +
>>   static void
>>   intel_dp_detect_sdp_caps(struct intel_dp *intel_dp)
>>   {
>> @@ -6308,6 +6342,9 @@ intel_dp_detect_sdp_caps(struct intel_dp *intel_dp)
>>   
>>   	intel_dp->as_sdp_supported = HAS_AS_SDP(display) &&
>>   		drm_dp_as_sdp_supported(&intel_dp->aux, intel_dp->dpcd);
>> +
>> +	intel_dp->as_sdp_v2_supported = intel_dp->as_sdp_supported &&
>> +					intel_dp_sink_supports_as_sdp_v2(intel_dp);
>>   }
>>   
>>   static bool intel_dp_needs_dpcd_probe(struct intel_dp *intel_dp, bool force_on_external)
>> -- 
>> 2.45.2