Re: [PATCH 3/6] drm/msm/dp: Limit voltage swing level to 2 for RA620 bridge

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] A device-specific workaround for the RA620 bridge is applied globally, capping the maximum voltage swing and pre-emphasis levels for all DP devices using the MSM DP driver.
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commit cfc03fd78122eb643ca94e4cccdc197ffa9a8de0
Author: Graham O'Connor <graham.oconnor@gmail.com>

drm/msm/dp: Limit voltage swing level to 2 for RA620 bridge

This commit reduces the maximum DisplayPort link training level to 2 to work
around a link training failure specific to the RA620 DP-to-HDMI bridge used
on the Radxa Dragon Q6A platform.

> diff --git a/drivers/gpu/drm/msm/dp/dp_link.h b/drivers/gpu/drm/msm/dp/dp_link.h
> index 76125e9c07e9c..ff0d8e99d87c9 100644
> --- a/drivers/gpu/drm/msm/dp/dp_link.h
> +++ b/drivers/gpu/drm/msm/dp/dp_link.h
> @@ -24,7 +24,7 @@ struct msm_dp_link_info {
>  	unsigned long capabilities;
>  };
>  
> -#define DP_TRAIN_LEVEL_MAX	3
> +#define DP_TRAIN_LEVEL_MAX	2

[Severity: High]
Does this change globally cap the maximum voltage swing and pre-emphasis
levels for all DisplayPort devices using the MSM DP driver?

Because the DP specification supports voltage swing up to level 3, which is
often required for signal integrity over long cables or at high bandwidths,
removing this capability globally can cause link training failures and
unstable connections on fully compliant displays.

Furthermore, since maximum pre-emphasis is calculated as DP_TRAIN_LEVEL_MAX
minus the voltage level, capping this macro at 2 means that if a voltage
swing level of 2 is used, the pre-emphasis level is strictly constrained to 0.

Could this hardware-specific workaround for the RA620 bridge be implemented
conditionally (for example, via DPCD OUI detection, bridge properties, or
device tree matching) rather than permanently degrading global subsystem
capabilities for all platforms?

>  
>  struct msm_dp_link_test_video {
>  	u32 test_video_pattern;

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Sashiko AI review · https://sashiko.dev/#/patchset/20260522060645.4399-1-graham.oconnor@gmail.com?part=3