drm: Simplify and defend later checks when disabling a crtc

By setting the FB of a CRTC to NULL, we are turning off the CRTC (and so
disable the unused encoders and connectors). As such we can simplify the
later tests by making sure the set->mode is NULL. Setting the
num_connectors to zero means that we do not need to loop over the unused
connectors.

All current usage appears correct, this only builds additional defense
into the routine.

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

1 files changed, 6 insertions, 3 deletions

diff --git a/drivers/gpu/drm/drm_crtc_helper.c b/drivers/gpu/drm/drm_crtc_helper.c
index 468e8e16c806..c4178d7c6a08 100644
--- a/drivers/gpu/drm/drm_crtc_helper.c
+++ b/drivers/gpu/drm/drm_crtc_helper.c
@@ -497,14 +497,17 @@ int drm_crtc_helper_set_config(struct drm_mode_set *set)
 
         crtc_funcs = set->crtc->helper_private;
 
+        if (!set->mode)
+                set->fb = NULL;
+
         if (set->fb) {
                 DRM_DEBUG_KMS("[CRTC:%d] [FB:%d] #connectors=%d (x y) (%i %i)\n",
                                 set->crtc->base.id, set->fb->base.id,
                                 (int)set->num_connectors, set->x, set->y);
         } else {
-                DRM_DEBUG_KMS("[CRTC:%d] [NOFB] #connectors=%d (x y) (%i %i)\n",
-                                set->crtc->base.id, (int)set->num_connectors,
-                                set->x, set->y);
+                DRM_DEBUG_KMS("[CRTC:%d] [NOFB]\n", set->crtc->base.id);
+                set->mode = NULL;
+                set->num_connectors = 0;
         }
 
         dev = set->crtc->dev;