drm: mxsfb: Implement .format_mod_supported

This will make sure applications which use the IN_FORMATS blob
to figure out which modifiers they can use will pick up the
linear modifier which is needed by mxsfb. Such applications
will not work otherwise if an incompatible implicit modifier
ends up being selected.

Before commit ae1ed009 ("drm: mxsfb: Stop using DRM simple
display pipeline helper"), the DRM simple display pipeline
helper took care of this.
Signed-off-by: Daniel Abrecht <public@danielabrecht.ch>
Fixes: ae1ed009 ("drm: mxsfb: Stop using DRM simple display pipeline helper")
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/2a99ffffc2378209307e0992a6e97e70@nodmarc.danielabrecht.ch

drivers/gpu/drm/mxsfb/mxsfb_kms.c

@@ -486,6 +486,13 @@ static void mxsfb_plane_overlay_atomic_update(struct drm_plane *plane,
 	writel(ctrl, mxsfb->base + LCDC_AS_CTRL);
 }
 
+static bool mxsfb_format_mod_supported(struct drm_plane *plane,
+				       uint32_t format,
+				       uint64_t modifier)
+{
+	return modifier == DRM_FORMAT_MOD_LINEAR;
+}
+
 static const struct drm_plane_helper_funcs mxsfb_plane_primary_helper_funcs = {
 	.atomic_check = mxsfb_plane_atomic_check,
 	.atomic_update = mxsfb_plane_primary_atomic_update,
@@ -497,6 +504,7 @@ static const struct drm_plane_helper_funcs mxsfb_plane_overlay_helper_funcs = {
 };
 
 static const struct drm_plane_funcs mxsfb_plane_funcs = {
+	.format_mod_supported	= mxsfb_format_mod_supported,
 	.update_plane		= drm_atomic_helper_update_plane,
 	.disable_plane		= drm_atomic_helper_disable_plane,
 	.destroy		= drm_plane_cleanup,