Patch "drm/amd/display: Fix DSC-re-computing" has been added to the 6.6-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    drm/amd/display: Fix DSC-re-computing

to the 6.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     drm-amd-display-fix-dsc-re-computing.patch
and it can be found in the queue-6.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 6c2f9aa834ccdc6080a18cd85574238abe914960
Author: Agustin Gutierrez <agustin.gutierrez@xxxxxxx>
Date:   Fri Apr 19 13:53:52 2024 -0400

    drm/amd/display: Fix DSC-re-computing
    
    [ Upstream commit b9b5a82c532109a09f4340ef5cabdfdbb0691a9d ]
    
    [Why]
    This fixes a bug introduced by commit c53655545141 ("drm/amd/display: dsc
    mst re-compute pbn for changes on hub").
    The change caused light-up issues with a second display that required
    DSC on some MST docks.
    
    [How]
    Use Virtual DPCD for DSC caps in MST case.
    
    [Limitations]
    This change only affects MST DSC devices that follow specifications
    additional changes are required to check for old MST DSC devices such as
    ones which do not check for Virtual DPCD registers.
    
    Reviewed-by: Swapnil Patel <swapnil.patel@xxxxxxx>
    Reviewed-by: Hersen Wu <hersenxs.wu@xxxxxxx>
    Acked-by: Tom Chung <chiahsuan.chung@xxxxxxx>
    Signed-off-by: Agustin Gutierrez <agustin.gutierrez@xxxxxxx>
    Tested-by: Daniel Wheeler <daniel.wheeler@xxxxxxx>
    Signed-off-by: Alex Deucher <alexander.deucher@xxxxxxx>
    Stable-dep-of: 4641169a8c95 ("drm/amd/display: Fix incorrect DSC recompute trigger")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
index 9ec9792f115a..b4bbd3be35a6 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
@@ -1219,10 +1219,6 @@ static bool is_dsc_need_re_compute(
 	if (dc_link->type != dc_connection_mst_branch)
 		return false;
 
-	if (!(dc_link->dpcd_caps.dsc_caps.dsc_basic_caps.fields.dsc_support.DSC_SUPPORT ||
-		dc_link->dpcd_caps.dsc_caps.dsc_basic_caps.fields.dsc_support.DSC_PASSTHROUGH_SUPPORT))
-		return false;
-
 	for (i = 0; i < MAX_PIPES; i++)
 		stream_on_link[i] = NULL;
 
@@ -1240,7 +1236,19 @@ static bool is_dsc_need_re_compute(
 			continue;
 
 		aconnector = (struct amdgpu_dm_connector *) stream->dm_stream_context;
-		if (!aconnector)
+		if (!aconnector || !aconnector->dsc_aux)
+			continue;
+
+		/*
+		 *	Check if cached virtual MST DSC caps are available and DSC is supported
+		 *	this change takes care of newer MST DSC capable devices that report their
+		 *	DPCD caps as per specifications in their Virtual DPCD registers.
+
+		 *	TODO: implement the check for older MST DSC devices that do not conform to
+		 *	specifications.
+		*/
+		if (!(aconnector->dc_sink->dsc_caps.dsc_dec_caps.is_dsc_supported ||
+			aconnector->dc_link->dpcd_caps.dsc_caps.dsc_basic_caps.fields.dsc_support.DSC_PASSTHROUGH_SUPPORT))
 			continue;
 
 		stream_on_link[new_stream_on_link_num] = aconnector;