drm/amdgpu: Read vram width from integrated system info table

On KB, KV, CZ we should read the vram width from integrated system
table, if we can. The NOOFCHAN in MC_SHARED_CHMAP is not accurate.

With this change we can enable two 4k displays on CZ again. This use
case was broken sometime in January when we started looking at
vram_width for bandwidth calculations instead of hardcoding this value.

v2:
  Return 0 if integrated system info table is not available.

Tested-by: Roman Li <roman.li@amd.com>
Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

1 files changed, 29 insertions, 0 deletions

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_atombios.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_atombios.c
index f52b1bf3d3d9..ad4329922f79 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_atombios.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_atombios.c
@@ -754,6 +754,35 @@ union igp_info {
         struct _ATOM_INTEGRATED_SYSTEM_INFO_V1_9 info_9;
 };
 
+/*
+ * Return vram width from integrated system info table, if available,
+ * or 0 if not.
+ */
+int amdgpu_atombios_get_vram_width(struct amdgpu_device *adev)
+{
+        struct amdgpu_mode_info *mode_info = &adev->mode_info;
+        int index = GetIndexIntoMasterTable(DATA, IntegratedSystemInfo);
+        u16 data_offset, size;
+        union igp_info *igp_info;
+        u8 frev, crev;
+
+        /* get any igp specific overrides */
+        if (amdgpu_atom_parse_data_header(mode_info->atom_context, index, &size,
+                                   &frev, &crev, &data_offset)) {
+                igp_info = (union igp_info *)
+                        (mode_info->atom_context->bios + data_offset);
+                switch (crev) {
+                case 8:
+                case 9:
+                        return igp_info->info_8.ucUMAChannelNumber * 64;
+                default:
+                        return 0;
+                }
+        }
+
+        return 0;
+}
+
 static void amdgpu_atombios_get_igp_ss_overrides(struct amdgpu_device *adev,
                                                  struct amdgpu_atom_ss *ss,
                                                  int id)