drm/amd/display: Add Debugfs Entry to Force in SST Sequence

It is to force SST sequence on MST capable receivers.

v2: squash in compilation fix when CONFIG_DRM_AMD_DC_DCN is not set
Signed-off-by: Fangzhi Zuo <Jerry.Zuo@amd.com>
Reviewed-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_debugfs.c

@@ -3237,6 +3237,32 @@ static int disable_hpd_get(void *data, u64 *val)
 DEFINE_DEBUGFS_ATTRIBUTE(disable_hpd_ops, disable_hpd_get,
 			 disable_hpd_set, "%llu\n");
 
+#if defined(CONFIG_DRM_AMD_DC_DCN)
+/*
+ * Temporary w/a to force sst sequence in M42D DP2 mst receiver
+ * Example usage: echo 1 > /sys/kernel/debug/dri/0/amdgpu_dm_dp_set_mst_en_for_sst
+ */
+static int dp_force_sst_set(void *data, u64 val)
+{
+	struct amdgpu_device *adev = data;
+
+	adev->dm.dc->debug.set_mst_en_for_sst = val;
+
+	return 0;
+}
+
+static int dp_force_sst_get(void *data, u64 *val)
+{
+	struct amdgpu_device *adev = data;
+
+	*val = adev->dm.dc->debug.set_mst_en_for_sst;
+
+	return 0;
+}
+DEFINE_DEBUGFS_ATTRIBUTE(dp_set_mst_en_for_sst_ops, dp_force_sst_get,
+			 dp_force_sst_set, "%llu\n");
+#endif
+
 /*
  * Sets the DC visual confirm debug option from the given string.
  * Example usage: echo 1 > /sys/kernel/debug/dri/0/amdgpu_visual_confirm
@@ -3346,6 +3372,10 @@ void dtn_debugfs_init(struct amdgpu_device *adev)
 			    adev, &mst_topo_fops);
 	debugfs_create_file("amdgpu_dm_dtn_log", 0644, root, adev,
 			    &dtn_log_fops);
+#if defined(CONFIG_DRM_AMD_DC_DCN)
+	debugfs_create_file("amdgpu_dm_dp_set_mst_en_for_sst", 0644, root, adev,
+				&dp_set_mst_en_for_sst_ops);
+#endif
 
 	debugfs_create_file_unsafe("amdgpu_dm_visual_confirm", 0644, root, adev,
 				   &visual_confirm_fops);