drm: Don't switch fb when disabling an output

In drm_crtc_helper_set_config, we call drm_crtc_helper_set_mode which
may return early and do no operation if the crtc is to be disabled. In
this case we merrily swap to the new fb, discarding the old_fb believing
that it has been cleaned up. However, due to the early return, the
old_fb was not presented to the backend for correct reaping, and nor was
the new one - which is about to be reaped via the
drm_helper_disable_unused_functions(), leading to incorrect refcounting
of the pinned objects.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=27722
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=29857
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=29230
Tested-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 2 insertions, 2 deletions

diff --git a/drivers/gpu/drm/drm_crtc_helper.c b/drivers/gpu/drm/drm_crtc_helper.c
index 952b3d4fb2a6..468e8e16c806 100644
--- a/drivers/gpu/drm/drm_crtc_helper.c
+++ b/drivers/gpu/drm/drm_crtc_helper.c
@@ -649,8 +649,8 @@ int drm_crtc_helper_set_config(struct drm_mode_set *set)
                 mode_changed = true;
 
         if (mode_changed) {
-                set->crtc->enabled = (set->mode != NULL);
-                if (set->mode != NULL) {
+                set->crtc->enabled = drm_helper_crtc_in_use(set->crtc);
+                if (set->crtc->enabled) {
                         DRM_DEBUG_KMS("attempting to set mode from"
                                         " userspace\n");
                         drm_mode_debug_printmodeline(set->mode);