drm: Handle ->disable_plane failures correctly

The ->disable_plane hook always had a return value, but only since the
introduction of primary planes was there any implementation that
actually failed.

So handle such failures correctly.

Note that drm_plane_force_disable is special: In the modeset cleanup
case we first disable all crtc, so primary planes should all be freed
already. And in the fb helper we only reset non-primary planes. Still
better be paranoid and add an early return.

I don't see how this could happen, but it might fix the fb refcount
underrun Thierry is seeing. Matt Roper spotted this issue.

Cc: Thierry Reding <treding@nvidia.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 10 insertions, 4 deletions

diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index f6633cb927bc..461d19bd14ee 100644
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -1152,8 +1152,10 @@ void drm_plane_force_disable(struct drm_plane *plane)
                 return;
 
         ret = plane->funcs->disable_plane(plane);
-        if (ret)
+        if (ret) {
                 DRM_ERROR("failed to disable plane with busy fb\n");
+                return;
+        }
         /* disconnect the plane from the fb and crtc: */
         __drm_framebuffer_unreference(old_fb);
         plane->fb = NULL;
@@ -2117,9 +2119,13 @@ int drm_mode_setplane(struct drm_device *dev, void *data,
         if (!plane_req->fb_id) {
                 drm_modeset_lock_all(dev);
                 old_fb = plane->fb;
-                plane->funcs->disable_plane(plane);
-                plane->crtc = NULL;
-                plane->fb = NULL;
+                ret = plane->funcs->disable_plane(plane);
+                if (!ret) {
+                        plane->crtc = NULL;
+                        plane->fb = NULL;
+                } else {
+                        old_fb = NULL;
+                }
                 drm_modeset_unlock_all(dev);
                 goto out;
         }