drm/amd/display: Add writeback enable field (wb_enabled)

[WHAT]
Add a new field to keep track whether a crtc is previously
writeback-enabled.

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_mode.h

@@ -418,6 +418,7 @@ struct amdgpu_crtc {
 	struct drm_pending_vblank_event *event;
 
 	bool wb_pending;
+	bool wb_enabled;
 	struct drm_writeback_connector *wb_conn;
 };
 

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

@@ -8732,9 +8732,13 @@ static void amdgpu_dm_commit_streams(struct drm_atomic_state *state,
 		if (acrtc)
 			old_crtc_state = drm_atomic_get_old_crtc_state(state, &acrtc->base);
 
+		if (!acrtc->wb_enabled)
+			continue;
+
 		dm_old_crtc_state = to_dm_crtc_state(old_crtc_state);
 
 		dm_clear_writeback(dm, dm_old_crtc_state);
+		acrtc->wb_enabled = false;
 	}
 
 	for_each_oldnew_crtc_in_state(state, crtc, old_crtc_state,
@@ -9312,9 +9316,13 @@ static void amdgpu_dm_atomic_commit_tail(struct drm_atomic_state *state)
 		if (acrtc)
 			new_crtc_state = drm_atomic_get_new_crtc_state(state, &acrtc->base);
 
+		if (acrtc->wb_enabled)
+			continue;
+
 		dm_new_crtc_state = to_dm_crtc_state(new_crtc_state);
 
 		dm_set_writeback(dm, dm_new_crtc_state, connector, new_con_state);
+		acrtc->wb_enabled = true;
 	}
 
 	/* Update audio instances for each connector. */