drm/amd/display: Return invalid state if GPINT times out

[Why]
GPINT timeout is causing PSR_STATE_0 to be returned when it shouldn't.
We must guarantee that PSR is fully disabled before doing hw programming
on driver-side.

[How]
Return invalid state if GPINT command times out. Let existing retry
logic send the GPINT until successful.
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Wyatt Wood <wyatt.wood@amd.com>
Reviewed-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dce/dmub_psr.c

@@ -81,13 +81,18 @@ static void dmub_psr_get_state(struct dmub_psr *dmub, enum dc_psr_state *state)
 {
 	struct dmub_srv *srv = dmub->ctx->dmub_srv->dmub;
 	uint32_t raw_state;
+	enum dmub_status status = DMUB_STATUS_INVALID;
 
 	// Send gpint command and wait for ack
-	dmub_srv_send_gpint_command(srv, DMUB_GPINT__GET_PSR_STATE, 0, 30);
+	status = dmub_srv_send_gpint_command(srv, DMUB_GPINT__GET_PSR_STATE, 0, 30);
 
+	if (status == DMUB_STATUS_OK) {
+		// GPINT was executed, get response
 		dmub_srv_get_gpint_response(srv, &raw_state);
-
 		*state = convert_psr_state(raw_state);
+	} else
+		// Return invalid state when GPINT times out
+		*state = 0xFF;
 }
 
 /*