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

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

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.

> +			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

-- 
Ville Syrjälä
Intel