drm/ssd130x: 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.

v6:
	* update patch for ssd132x support
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Tested-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231009141018.11291-8-tzimmermann@suse.de

drivers/gpu/drm/solomon/ssd130x.c

@@ -873,6 +873,7 @@ static int ssd130x_primary_plane_atomic_check(struct drm_plane *plane,
 	struct ssd130x_device *ssd130x = drm_to_ssd130x(drm);
 	struct drm_plane_state *plane_state = drm_atomic_get_new_plane_state(state, plane);
 	struct ssd130x_plane_state *ssd130x_state = to_ssd130x_plane_state(plane_state);
+	struct drm_shadow_plane_state *shadow_plane_state = &ssd130x_state->base;
 	struct drm_crtc *crtc = plane_state->crtc;
 	struct drm_crtc_state *crtc_state = NULL;
 	const struct drm_format_info *fi;
@@ -897,6 +898,16 @@ static int ssd130x_primary_plane_atomic_check(struct drm_plane *plane,
 
 	pitch = drm_format_info_min_pitch(fi, 0, ssd130x->width);
 
+	if (plane_state->fb->format != fi) {
+		void *buf;
+
+		/* format conversion necessary; reserve buffer */
+		buf = drm_format_conv_state_reserve(&shadow_plane_state->fmtcnv_state,
+						    pitch, GFP_KERNEL);
+		if (!buf)
+			return -ENOMEM;
+	}
+
 	ssd130x_state->buffer = kcalloc(pitch, ssd130x->height, GFP_KERNEL);
 	if (!ssd130x_state->buffer)
 		return -ENOMEM;
@@ -911,6 +922,7 @@ static int ssd132x_primary_plane_atomic_check(struct drm_plane *plane,
 	struct ssd130x_device *ssd130x = drm_to_ssd130x(drm);
 	struct drm_plane_state *plane_state = drm_atomic_get_new_plane_state(state, plane);
 	struct ssd130x_plane_state *ssd130x_state = to_ssd130x_plane_state(plane_state);
+	struct drm_shadow_plane_state *shadow_plane_state = &ssd130x_state->base;
 	struct drm_crtc *crtc = plane_state->crtc;
 	struct drm_crtc_state *crtc_state = NULL;
 	const struct drm_format_info *fi;
@@ -935,6 +947,16 @@ static int ssd132x_primary_plane_atomic_check(struct drm_plane *plane,
 
 	pitch = drm_format_info_min_pitch(fi, 0, ssd130x->width);
 
+	if (plane_state->fb->format != fi) {
+		void *buf;
+
+		/* format conversion necessary; reserve buffer */
+		buf = drm_format_conv_state_reserve(&shadow_plane_state->fmtcnv_state,
+						    pitch, GFP_KERNEL);
+		if (!buf)
+			return -ENOMEM;
+	}
+
 	ssd130x_state->buffer = kcalloc(pitch, ssd130x->height, GFP_KERNEL);
 	if (!ssd130x_state->buffer)
 		return -ENOMEM;