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 <[e-mail]>
Reviewed-by: Javier Martinez Canillas <[e-mail]>
Tested-by: Javier Martinez Canillas <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/solomon/ssd130x.c

···
 	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;
···
 
 	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;
···
 	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;
···
 		return -EINVAL;
 
 	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)