Re: [PATCH 14/23] drm/i915/dp: Add member to intel_dp to store AS SDP v2 support

Nautiyal, Ankit K
2026-04-07T08:20:23Z

On 4/2/2026 6:20 PM, Ville Syrjälä wrote:
> On Thu, Apr 02, 2026 at 02:04:28PM +0300, Ville Syrjälä wrote:
>> On Thu, Apr 02, 2026 at 01:34:14PM +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 introduces ASYNC_VIDEO_TIMING_NOT_SUPPORTED_IN_PR in the
>>> Panel Replay Capability DPCD 0x00b1 (Bit 3). When this bit is set, the sink
>>> does not support asynchronous video timing while in a Panel Replay Active
>>> state and the source is required to keep transmitting Adaptive-Sync
>>> SDPs. 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.
>> Hmm. After some more reading I think we might actually want to consult
>> the DisplayID for this. The presence of the new adaptive sync block
>> there might be a good indication for AS SDP v2 support. While the
>> DisplayID 2.1 spec itself doesn't say that AS SDP v2 must be supported
>> when the block is present, the DP 2.1 spec does at least say the converse.
>> Ie. adaptive sync capable DP 2.1 sink must have the DisplayID block. And
>> DP 2.1 seems to be all about the AS SDP v2 and not AS SDP v1 (that's a DP
>> 2.0 thing really).
> Hmm. But the EDID comes from the display, and we could have a PCON
> in between that doesn't understand AS SDP v2. Sigh. What a mess.

hmm yeah. Is it alright to have a #TODO something like:

/*
* TODO: Check the Adaptive-Sync DisplayID 2.1 block once DisplayID parsing
* is available. This may help detect AS SDP v2 support for native DP 2.1
* sinks that do not expose FAVT or PR-based capability bits.
*
* In the presence of PCONs, check PCON support from DPCD and sink
support from Display ID.
*/

Regards,

Ankit

>> I think there was a patch posted very recently on dri-devel, adding the
>> adaptive sync DisplayID block parsing. Or at least some DisplayID block
>> related to this.
>>
>> The intel_psr_pr_async_video_timing_supported() check I think we want
>> to keep regardless, because you could have a sink with PR but no
>> adaptive sync. But the FAVT check could perhaps be dropped if we add
>> the DisplayID check.
>>
>>> v2: Include parsing ASYNC_VIDEO_TIMING_NOT_SUPPORTED_IN_PR bit to
>>> determine AS SDP v2 support. (Ville)
>>> v3: Use helper to determine asynch video timing support.
>>>
>>> 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 | 33 +++++++++++++++++++
>>> 2 files changed, 34 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 cec0f3d03c2f..9fd768447f28 100644
>>> --- a/drivers/gpu/drm/i915/display/intel_dp.c
>>> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
>>> @@ -6306,6 +6306,36 @@ 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;
>>> +
>>> + /*
>>> + * 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 indicates that the sink
>>> + * does not support asynchronous video timing while in PR Active,
>>> + * requiring the source to keep transmitting Adaptive-Sync SDPs. 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 (!intel_psr_pr_async_video_timing_supported(intel_dp))
>>> + return true;
>>> +
>>> + return false;
>>> +}
>>> +
>>> static void
>>> intel_dp_detect_sdp_caps(struct intel_dp *intel_dp)
>>> {
>>> @@ -6313,6 +6343,9 @@ 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
>> --
>> Ville Syrjälä
>> Intel