drm/ofdrm: Preallocate format-conversion buffer in atomic_check

Preallocate the format-conversion state's storage in the plane's
atomic_check function if a format conversion is necessary. Allows
the update to fail if no memory is available. Avoids the same
allocation within atomic_update, which may not fail.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231009141018.11291-5-tzimmermann@suse.de

drivers/gpu/drm/tiny/ofdrm.c

@@ -758,7 +758,11 @@ static const uint64_t ofdrm_primary_plane_format_modifiers[] = {
 static int ofdrm_primary_plane_helper_atomic_check(struct drm_plane *plane,
 						   struct drm_atomic_state *new_state)
 {
+	struct drm_device *dev = plane->dev;
+	struct ofdrm_device *odev = ofdrm_device_of_dev(dev);
 	struct drm_plane_state *new_plane_state = drm_atomic_get_new_plane_state(new_state, plane);
+	struct drm_shadow_plane_state *new_shadow_plane_state =
+		to_drm_shadow_plane_state(new_plane_state);
 	struct drm_framebuffer *new_fb = new_plane_state->fb;
 	struct drm_crtc *new_crtc = new_plane_state->crtc;
 	struct drm_crtc_state *new_crtc_state = NULL;
@@ -777,6 +781,16 @@ static int ofdrm_primary_plane_helper_atomic_check(struct drm_plane *plane,
 	else if (!new_plane_state->visible)
 		return 0;
 
+	if (new_fb->format != odev->format) {
+		void *buf;
+
+		/* format conversion necessary; reserve buffer */
+		buf = drm_format_conv_state_reserve(&new_shadow_plane_state->fmtcnv_state,
+						    odev->pitch, GFP_KERNEL);
+		if (!buf)
+			return -ENOMEM;
+	}
+
 	new_crtc_state = drm_atomic_get_new_crtc_state(new_state, new_plane_state->crtc);
 
 	new_ofdrm_crtc_state = to_ofdrm_crtc_state(new_crtc_state);