Re: [PATCH 2/3] drm/amd/display: Wait up to 1 s for slow sinks in FRL link training

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Medium] drm/amd/display: unconditional 1s LTS:3 timeout violates HDMI
  T_FLT spec
--

commit 2cb267c6df8cc9565556b092b803e0c5c55db242
Author: Andrzej Piątyszek <andrzej.piatyszek@gmail.com>

drm/amd/display: Wait up to 1 s for slow sinks in FRL link training

This commit increases the FRL link training state 3 (LTS:3) polling timeout
in hdmi_frl_perform_link_training() to 1 second across all link rates to
accommodate slow HDMI sinks.

> diff --git a/drivers/gpu/drm/amd/display/dc/link/protocols/link_hdmi_frl.c b/drivers/gpu/drm/amd/display/dc/link/protocols/link_hdmi_frl.c
> index 78e62bfec49c7..97b2b9b74cc71 100644
> --- a/drivers/gpu/drm/amd/display/dc/link/protocols/link_hdmi_frl.c
> +++ b/drivers/gpu/drm/amd/display/dc/link/protocols/link_hdmi_frl.c
> @@ -612,10 +612,13 @@ static enum link_result hdmi_frl_perform_link_training(struct ddc_service *ddc_s
>  
>  		FRL_INFO("FRL LINK TRAINING:  Poll for FLT_UPDATE.\n");
>  		/*LTS:3: Start Link Training*/
> -		/*Start FLT Timer = 200 ms, or 300ms if link rate >= 16Gbps*/
> +		/*
> +		 * Start FLT Timer. Some sinks need longer than the nominal 200 ms
> +		 * (300 ms at 16 Gbps and above) to answer an LTP request, so wait
> +		 * up to 1 s before giving up on this rate.
> +		 */
>  		num_polls = 0;
> -		if (link_settings->frl_link_rate >= HDMI_FRL_LINK_RATE_16GBPS)
> -			poll_timeout_ns = 320 * 1000 * 1000;
> +		poll_timeout_ns = 1000 * 1000 * 1000;

[Severity: Medium]
Does setting poll_timeout_ns to 1 second unconditionally for all sinks break
HDMI 2.1/2.2 link layer compliance testing when test_req.fields.FLT_NO_TIMEOUT
is 0?

The HDMI specification limits the LTS:3 T_FLT timer to 200 ms nominal (220 ms
max) for rates below 16 Gbps and 300 ms nominal (320 ms max) for 16 Gbps and
above.  Commits f38686268b0d ("drm/amd/display: Fix HDMI2.2 LT timeout
duration"), 536ad3cf1871 ("drm/amd/display: Fix HDMI FRL FFE compliance test")
and 007834be6760 ("drm/amd/display: Adjust HDMI FRL LT timeout") specifically
tuned poll_timeout_ns to 220 ms and 320 ms so the elapsed time in LTS:3 does
not exceed the spec-defined limits during compliance tests.  Could the 1 second
timeout be applied only to affected displays via an EDID quirk instead?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261110130956.160024-1-andrzej.piatyszek@gmail.com?part=2