[PATCH 29/45] drm/amd/display: MST DSC check for older devices

[Tom Chung]

From: Agustin Gutierrez <agustin.gutier...@amd.com>

[Why]
Some older MST hubs do not report DPCD registers according to
specification.

[How]
This change re-applies change: c5365554514 "drm/amd/display: dsc mst
re-compute pbn for changes on hub".
With an additional check for these older MST devices.

Reviewed-by: Swapnil Patel <swapnil.pa...@amd.com>
Acked-by: Tom Chung <chiahsuan.ch...@amd.com>
Signed-off-by: Agustin Gutierrez <agustin.gutier...@amd.com>
---
 .../amd/display/amdgpu_dm/amdgpu_dm_mst_types.c    | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

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 5542e7d63b81..affedce9de6b 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
@@ -1209,6 +1209,12 @@ static bool is_dsc_need_re_compute(
        if (dc_link->type != dc_connection_mst_branch)
                return false;
 
+       /* add a check for older MST DSC with no virtual DPCDs */
+       if (needs_dsc_aux_workaround(dc_link)  &&
+               
(!(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;
 
@@ -1230,12 +1236,8 @@ static bool is_dsc_need_re_compute(
                        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.
+                *      check if cached virtual MST DSC caps are available and 
DSC is supported
+                *      as per specifications in their Virtual DPCD registers.
                */
                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))
-- 
2.34.1