drm/bridge: tc358768: Default to positive h/v syncs

As the TC358768 is a DPI to DSI bridge, the DSI side does not need to
define h/v sync polarities. This means that sometimes we have a mode
without defined sync polarities, which does not work on the DPI side.

Add a mode_fixup hook to default to positive sync polarities.
Reviewed-by: Peter Ujfalusi <peter.ujfalusi@gmail.com>
Tested-by: Maxim Schwalm <maxim.schwalm@gmail.com> # Asus TF700T
Tested-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Robert Foss <rfoss@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230906-tc358768-v4-3-31725f008a50@ideasonboard.com

drivers/gpu/drm/bridge/tc358768.c

@@ -963,9 +963,27 @@ tc358768_atomic_get_input_bus_fmts(struct drm_bridge *bridge,
 	return input_fmts;
 }
 
+static bool tc358768_mode_fixup(struct drm_bridge *bridge,
+				const struct drm_display_mode *mode,
+				struct drm_display_mode *adjusted_mode)
+{
+	/* Default to positive sync */
+
+	if (!(adjusted_mode->flags &
+	      (DRM_MODE_FLAG_PHSYNC | DRM_MODE_FLAG_NHSYNC)))
+		adjusted_mode->flags |= DRM_MODE_FLAG_PHSYNC;
+
+	if (!(adjusted_mode->flags &
+	      (DRM_MODE_FLAG_PVSYNC | DRM_MODE_FLAG_NVSYNC)))
+		adjusted_mode->flags |= DRM_MODE_FLAG_PVSYNC;
+
+	return true;
+}
+
 static const struct drm_bridge_funcs tc358768_bridge_funcs = {
 	.attach = tc358768_bridge_attach,
 	.mode_valid = tc358768_bridge_mode_valid,
+	.mode_fixup = tc358768_mode_fixup,
 	.pre_enable = tc358768_bridge_pre_enable,
 	.enable = tc358768_bridge_enable,
 	.disable = tc358768_bridge_disable,