drm/amdgpu/mst: Stop ignoring error codes and deadlocking

It appears that amdgpu makes the mistake of completely ignoring the return
values from the DP MST helpers, and instead just returns a simple
true/false. In this case, it seems to have come back to bite us because as
a result of simply returning false from
compute_mst_dsc_configs_for_state(), amdgpu had no way of telling when a
deadlock happened from these helpers. This could definitely result in some
kernel splats.

V2:
* Address Wayne's comments (fix another bunch of spots where we weren't
  passing down return codes)
Signed-off-by: Lyude Paul <lyude@redhat.com>
Fixes: 8c20a1ed ("drm/amd/display: MST DSC compute fair share")
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: <stable@vger.kernel.org> # v5.6+
Reviewed-by: Wayne Lin <Wayne.Lin@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -6539,7 +6539,7 @@ static int dm_update_mst_vcpi_slots_for_dsc(struct drm_atomic_state *state,
 	struct drm_connector_state *new_con_state;
 	struct amdgpu_dm_connector *aconnector;
 	struct dm_connector_state *dm_conn_state;
-	int i, j;
+	int i, j, ret;
 	int vcpi, pbn_div, pbn, slot_num = 0;
 
 	for_each_new_connector_in_state(state, connector, new_con_state, i) {
@@ -6586,8 +6586,11 @@ static int dm_update_mst_vcpi_slots_for_dsc(struct drm_atomic_state *state,
 			dm_conn_state->pbn = pbn;
 			dm_conn_state->vcpi_slots = slot_num;
 
-			drm_dp_mst_atomic_enable_dsc(state, aconnector->port, dm_conn_state->pbn,
-						     false);
+			ret = drm_dp_mst_atomic_enable_dsc(state, aconnector->port,
+							   dm_conn_state->pbn, false);
+			if (ret < 0)
+				return ret;
+
 			continue;
 		}
 
@@ -9604,10 +9607,9 @@ static int amdgpu_dm_atomic_check(struct drm_device *dev,
 
 #if defined(CONFIG_DRM_AMD_DC_DCN)
 	if (dc_resource_is_dsc_encoding_supported(dc)) {
-		if (!pre_validate_dsc(state, &dm_state, vars)) {
-			ret = -EINVAL;
+		ret = pre_validate_dsc(state, &dm_state, vars);
+		if (ret != 0)
 			goto fail;
-		}
 	}
 #endif
 
@@ -9702,9 +9704,9 @@ static int amdgpu_dm_atomic_check(struct drm_device *dev,
 		}
 
 #if defined(CONFIG_DRM_AMD_DC_DCN)
-		if (!compute_mst_dsc_configs_for_state(state, dm_state->context, vars)) {
+		ret = compute_mst_dsc_configs_for_state(state, dm_state->context, vars);
+		if (ret) {
 			DRM_DEBUG_DRIVER("compute_mst_dsc_configs_for_state() failed\n");
-			ret = -EINVAL;
 			goto fail;
 		}
 

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.h

@@ -53,15 +53,15 @@ struct dsc_mst_fairness_vars {
 	struct amdgpu_dm_connector *aconnector;
 };
 
-bool compute_mst_dsc_configs_for_state(struct drm_atomic_state *state,
-				       struct dc_state *dc_state,
-				       struct dsc_mst_fairness_vars *vars);
+int compute_mst_dsc_configs_for_state(struct drm_atomic_state *state,
+				      struct dc_state *dc_state,
+				      struct dsc_mst_fairness_vars *vars);
 
 bool needs_dsc_aux_workaround(struct dc_link *link);
 
-bool pre_validate_dsc(struct drm_atomic_state *state,
-		      struct dm_atomic_state **dm_state_ptr,
-		      struct dsc_mst_fairness_vars *vars);
+int pre_validate_dsc(struct drm_atomic_state *state,
+		     struct dm_atomic_state **dm_state_ptr,
+		     struct dsc_mst_fairness_vars *vars);
 
 enum dc_status dm_dp_mst_is_port_support_mode(
 	struct amdgpu_dm_connector *aconnector,