Re: [PATCH 6.12] drm/amd/display: Don't write DP_MSTM_CTRL after LT

[Jani Nikula <jani.nikula@linux.intel.com>]

On Mon, 31 Mar 2025, Thadeu Lima de Souza Cascardo <cascardo@igalia.com> wrote:
> From: Wayne Lin <Wayne.Lin@amd.com>
>
> [ Upstream commit bc068194f548ef1f230d96c4398046bf59165992 ]
>
> [Why]
> Observe after suspend/resme, we can't light up mst monitors under specific
> mst hub.

This is already at stable backport stage, but it would really be helpful
to log *which* specific mst hub we're talking about here. Now the
information is lost in time, at least to outsiders.

BR,
Jani.



> The reason is that driver still writes DPCD DP_MSTM_CTRL after LT.
> It's forbidden even we write the same value for that dpcd register.
>
> [How]
> We already resume the mst branch device dpcd settings during
> resume_mst_branch_status(). Leverage drm_dp_mst_topology_queue_probe() to
> only probe the topology, not calling drm_dp_mst_topology_mgr_resume() which
> will set DP_MSTM_CTRL as well.
>
> Reviewed-by: Jerry Zuo <jerry.zuo@amd.com>
> Signed-off-by: Wayne Lin <Wayne.Lin@amd.com>
> Signed-off-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
> Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@igalia.com>
> ---
>  .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c    | 16 ++++------------
>  1 file changed, 4 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> index d9a3917d207e..c4c6538eabae 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> @@ -3231,8 +3231,7 @@ static int dm_resume(void *handle)
>  	struct dm_atomic_state *dm_state = to_dm_atomic_state(dm->atomic_obj.state);
>  	enum dc_connection_type new_connection_type = dc_connection_none;
>  	struct dc_state *dc_state;
> -	int i, r, j, ret;
> -	bool need_hotplug = false;
> +	int i, r, j;
>  	struct dc_commit_streams_params commit_params = {};
>  
>  	if (dm->dc->caps.ips_support) {
> @@ -3427,23 +3426,16 @@ static int dm_resume(void *handle)
>  		    aconnector->mst_root)
>  			continue;
>  
> -		ret = drm_dp_mst_topology_mgr_resume(&aconnector->mst_mgr, true);
> -
> -		if (ret < 0) {
> -			dm_helpers_dp_mst_stop_top_mgr(aconnector->dc_link->ctx,
> -					aconnector->dc_link);
> -			need_hotplug = true;
> -		}
> +		drm_dp_mst_topology_queue_probe(&aconnector->mst_mgr);
>  	}
>  	drm_connector_list_iter_end(&iter);
>  
> -	if (need_hotplug)
> -		drm_kms_helper_hotplug_event(ddev);
> -
>  	amdgpu_dm_irq_resume_late(adev);
>  
>  	amdgpu_dm_smu_write_watermarks_table(adev);
>  
> +	drm_kms_helper_hotplug_event(ddev);
> +
>  	return 0;
>  }

-- 
Jani Nikula, Intel