drm/vc4: dpi: Ensure a default format is selected

In a couple of error/incomplete configuration cases, the
DPI_FORMAT bits wouldn't get set.

Enforce our RGB888 default in all these cases.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Link: https://lore.kernel.org/r/20220613144800.326124-11-maxime@cerno.tech
Signed-off-by: Maxime Ripard <maxime@cerno.tech>

drivers/gpu/drm/vc4/vc4_dpi.c

@@ -148,10 +148,15 @@ static void vc4_dpi_encoder_enable(struct drm_encoder *encoder)
 	}
 	drm_connector_list_iter_end(&conn_iter);
 
+	/* Default to 24bit if no connector or format found. */
+	dpi_c |= VC4_SET_FIELD(DPI_FORMAT_24BIT_888_RGB, DPI_FORMAT);
+
 	if (connector) {
 		if (connector->display_info.num_bus_formats) {
 			u32 bus_format = connector->display_info.bus_formats[0];
 
+			dpi_c &= ~DPI_FORMAT_MASK;
+
 			switch (bus_format) {
 			case MEDIA_BUS_FMT_RGB888_1X24:
 				dpi_c |= VC4_SET_FIELD(DPI_FORMAT_24BIT_888_RGB,
@@ -187,9 +192,6 @@ static void vc4_dpi_encoder_enable(struct drm_encoder *encoder)
 
 		if (connector->display_info.bus_flags & DRM_BUS_FLAG_DE_LOW)
 			dpi_c |= DPI_OUTPUT_ENABLE_INVERT;
-	} else {
-		/* Default to 24bit if no connector found. */
-		dpi_c |= VC4_SET_FIELD(DPI_FORMAT_24BIT_888_RGB, DPI_FORMAT);
 	}
 
 	if (mode->flags & DRM_MODE_FLAG_CSYNC) {