drm/fb-helper: Unmap client buffer during shutdown

The fbdev helper's generic probe function establishes a mapping for
framebuffers without shadow buffer. The clean-up function did not unmap
the buffer object. Add the unmap operation.

As fbdev devices are usally released during system shutdown, this has
not been a problem in practice.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20201120102545.4047-3-tzimmermann@suse.de

drivers/gpu/drm/drm_fb_helper.c

@@ -1988,14 +1988,19 @@ static void drm_fbdev_cleanup(struct drm_fb_helper *fb_helper)
 	if (!fb_helper->dev)
 		return;
 
-	if (fbi && fbi->fbdefio) {
+	if (fbi) {
+		if (fbi->fbdefio)
 			fb_deferred_io_cleanup(fbi);
+		if (drm_fbdev_use_shadow_fb(fb_helper))
 			shadow = fbi->screen_buffer;
 	}
 
 	drm_fb_helper_fini(fb_helper);
 
+	if (shadow)
 		vfree(shadow);
+	else
+		drm_client_buffer_vunmap(fb_helper->buffer);
 
 	drm_client_framebuffer_delete(fb_helper->buffer);
 }