Re: [PATCH v2] drm/i915/display: Take into account AS SDP in intel_dp_sdp_min_guardband

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

On 10/23/2025 10:01 AM, Jouni Högander wrote:
> We started seeing "[drm] *ERROR* Timed out waiting PSR idle state" after
> taking optimized guardband into use. These are seen because VSC SDPs are
> sent on same line as AS SDPs when AS SDP is enabled. AS SDP is sent on line
> configured in EMP_AS_SDP_TL register. We are configuring
> crtc_state->vrr.vsync_start into that register.
>
> Fix this by ensuring AS SDP is sent on line which is within
> guardband. From the bspec:
>
> EMP_AS_SDP_TL < SCL + Guardband
>
> v2: check HAS_AS_SDP
>
> Bspec: 71197
> Fixes: 52ecd48b8d3f ("drm/i915/dp: Add helper to get min sdp guardband")
> Cc: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
> Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
> ---
>   drivers/gpu/drm/i915/display/intel_dp.c | 16 +++++++++++++---
>   1 file changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 475518b4048b7..a3391b17571cf 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -7023,7 +7023,7 @@ int intel_dp_compute_config_late(struct intel_encoder *encoder,
>   }
>   
>   static
> -int intel_dp_get_lines_for_sdp(u32 type)
> +int intel_dp_get_lines_for_sdp(const struct intel_crtc_state *crtc_state, u32 type)
>   {
>   	switch (type) {
>   	case DP_SDP_VSC_EXT_VESA:
> @@ -7033,6 +7033,8 @@ int intel_dp_get_lines_for_sdp(u32 type)
>   		return 8;
>   	case DP_SDP_PPS:
>   		return 7;
> +	case DP_SDP_ADAPTIVE_SYNC:
> +		return crtc_state->vrr.vsync_start + 1;


Hmm.. currently vrr.vsync_start is (vtotal - mode->vsync_start), 
returning this will effectively make the guardband as full vblank length.

So we will not have optimized guardband any more.

The issue as highlighted in commit message is the problem with 
EMP_AS_SDP_TL which is set to vrr.vsync_start.

This was working when guardband was full vblank length, but with 
optimized guardband the transmission line is no more in (SCL + 
guardband) region.

I have sent a patch to fix the transmission line : 
https://patchwork.freedesktop.org/patch/683034/?series=156411&rev=1


Regards,

Ankit

>   	default:
>   		break;
>   	}
> @@ -7043,17 +7045,25 @@ int intel_dp_get_lines_for_sdp(u32 type)
>   int intel_dp_sdp_min_guardband(const struct intel_crtc_state *crtc_state,
>   			       bool assume_all_enabled)
>   {
> +	struct intel_display *display = to_intel_display(crtc_state);
>   	int sdp_guardband = 0;
>   
>   	if (assume_all_enabled ||
>   	    crtc_state->infoframes.enable &
>   	    intel_hdmi_infoframe_enable(HDMI_PACKET_TYPE_GAMUT_METADATA))
>   		sdp_guardband = max(sdp_guardband,
> -				    intel_dp_get_lines_for_sdp(HDMI_PACKET_TYPE_GAMUT_METADATA));
> +				    intel_dp_get_lines_for_sdp(crtc_state,
> +							       HDMI_PACKET_TYPE_GAMUT_METADATA));
>   
>   	if (assume_all_enabled ||
>   	    crtc_state->dsc.compression_enable)
> -		sdp_guardband = max(sdp_guardband, intel_dp_get_lines_for_sdp(DP_SDP_PPS));
> +		sdp_guardband = max(sdp_guardband,
> +				    intel_dp_get_lines_for_sdp(crtc_state, DP_SDP_PPS));
> +
> +	if ((assume_all_enabled && HAS_AS_SDP(display)) ||
> +	    crtc_state->infoframes.enable & intel_hdmi_infoframe_enable(DP_SDP_ADAPTIVE_SYNC))
> +		sdp_guardband = max(sdp_guardband,
> +				    intel_dp_get_lines_for_sdp(crtc_state, DP_SDP_ADAPTIVE_SYNC));
>   
>   	return sdp_guardband;
>   }