Re: [PATCH] drm/amd/display: Abort DPMS ON when enabling the link fails

[Wayne Lin <Wayne.Lin@amd.com>]

Reviewed-by: Wayne Lin <Wayne.Lin@amd.com>

On Wed, 28 Oct 2026 16:26:41 -0400, Abdulla Bubshait wrote:
> Since commit 843049bac7c0 ("drm/amd/display: Split DPMS ON into
> parts"), link_set_dpms_on_enable_link() returns
> DC_DPMS_FAILED_HANDSHAKE when enable_link() fails and the stream
> enable has to be aborted: any failure other than link training, or a
> link training failure on DP MST. The link has already been disabled at
> that point. The step loop in link_set_dpms_on() treats
> DC_DPMS_FAILED_HANDSHAKE like DC_DPMS_SUCCESS and goes on to
> link_set_dpms_on_post_enable_link().
>
> Before the split, this path returned right after disable_link(),
> because MST displays can't proceed without link training. Now, for
> failed MST handshakes MST slots are still allocated.  When the link
> trains again later, the new payload starts after the leaked slots so
> ACT never completes, and the display stays black until
> reboot. Replugging or power-cycling the monitor does not recover it.
>
> Seen on Navi 33 (DCN 3.2.1) with a DP 2.1 MST monitor (Odyssey Neo G9)
> at UHBR10 x4 with DSC. Link training sometimes fails on DPMS
> wake. With this change, the failed attempt leaves no payload behind,
> and the next modeset after the sink reconnects bring the monito back
> up.
>
> Return early on DC_DPMS_FAILED_HANDSHAKE, as for
> DC_DPMS_SKIPPED_HANDSHAKE. This restores the pre-split behaviour. Link
> training failures on non-MST signals still return DC_DPMS_SUCCESS and
> continue as before.
>
> Closes: https://gitlab.freedesktop.org/drm/amd/-/work_items/6047
> Fixes: 843049bac7c0 ("drm/amd/display: Split DPMS ON into parts")
> Cc: stable@vger.kernel.org # 7.3
> Signed-off-by: Abdulla Bubshait <darkstego@gmail.com>
> ---
>  drivers/gpu/drm/amd/display/dc/link/link_dpms.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/display/dc/link/link_dpms.c b/drivers/gpu/drm/amd/display/dc/link/link_dpms.c
> index 75e232ebffe8..b355e29b178d 100644
> --- a/drivers/gpu/drm/amd/display/dc/link/link_dpms.c
> +++ b/drivers/gpu/drm/amd/display/dc/link/link_dpms.c
> @@ -2813,11 +2813,11 @@ enum dc_status link_set_dpms_on(
>  
>  		switch (step_result) {
>  		case DC_DPMS_SUCCESS:
> -		case DC_DPMS_FAILED_HANDSHAKE:
>  			// Enum is ordered from "best" to "worst" results
>  			result = max(result, step_result);
>  			break;
>  
> +		case DC_DPMS_FAILED_HANDSHAKE:
>  		case DC_DPMS_SKIPPED_HANDSHAKE:
>  			return step_result;
>  
> -- 
> 2.56.0
>
>