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

[Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>]

On 5/22/26 8:06 AM, Graham O'Connor wrote:
> The RA620 DP-to-HDMI bridge used on the Radxa Dragon Q6A does not
> acknowledge DP link training at voltage swing level 3. The bridge
> requests maximum voltage swing but never completes link training
> when the driver attempts level 3, causing HDMI output to fail.
> 
> Cap DP_TRAIN_LEVEL_MAX at 2 to match the behaviour of the vendor
> kernel, where link training completes successfully at level 2.
> This allows the RA620 bridge to establish a stable HDMI connection.
> 
> Tested on Radxa Dragon Q6A (QCS6490) with RA620 DP-to-HDMI bridge
> 
> Signed-off-by: Graham O'Connor <graham.oconnor@gmail.com>
> ---
>  drivers/gpu/drm/msm/dp/dp_link.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/msm/dp/dp_link.h b/drivers/gpu/drm/msm/dp/dp_link.h
> index 76125e9c0..ff0d8e99d 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

You're limiting this value for *all* devices featuring a Qualcomm
SoC with a DP controller. Instead, if this is really an issue that
results from the bridge's capabilities (which could potentially only
be a symptom, not the cause), this should be somehow limited to the
specific bridge itself

Konrad