drm/ssd130x: Synchronize access to dma-buf imported GEM BOs

Synchronize CPU access to GEM BOs with other drivers when updating the
screen buffer. Imported DMA buffers might otherwise contain stale data.
Suggested-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20220927095249.1919385-1-javierm@redhat.com

drivers/gpu/drm/solomon/ssd130x.c

@@ -555,11 +555,18 @@ static int ssd130x_fb_blit_rect(struct drm_framebuffer *fb, const struct iosys_m
 	if (!buf)
 		return -ENOMEM;
 
+	ret = drm_gem_fb_begin_cpu_access(fb, DMA_FROM_DEVICE);
+	if (ret)
+		goto out_free;
+
 	iosys_map_set_vaddr(&dst, buf);
 	drm_fb_xrgb8888_to_mono(&dst, &dst_pitch, vmap, fb, rect);
 
+	drm_gem_fb_end_cpu_access(fb, DMA_FROM_DEVICE);
+
 	ssd130x_update_rect(ssd130x, buf, rect);
 
+out_free:
 	kfree(buf);
 
 	return ret;