Re: [PATCH 28/28] drm/atomic-helper: Reject legacy flips on a disabled pipe

On Fri, Dec 04, 2015 at 09:46:09AM +0100, Daniel Vetter wrote:

We want this for consistency with existing page_flip semantics.

Since this spurred quite a discussion on IRC also document why we reject even generation when the pipe is off: It's not that it's hard to implement, but userspace has a track recording proofing that it's way too easy to accidentally abuse and cause havoc. We want to make sure userspace doesn't get away with that.

Cc: Daniel Stone daniels@collabora.com Cc: Ville Syrjälä ville.syrjala@linux.intel.com Signed-off-by: Daniel Vetter daniel.vetter@ffwll.ch

---

drivers/gpu/drm/drm_atomic.c | 9 +++++++++ drivers/gpu/drm/drm_atomic_helper.c | 8 ++++++++ 2 files changed, 17 insertions(+)

diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c index 7426d40017a0..06cdb52907da 100644 --- a/drivers/gpu/drm/drm_atomic.c +++ b/drivers/gpu/drm/drm_atomic.c @@ -1265,6 +1265,15 @@ int drm_atomic_check_only(struct drm_atomic_state *state) if (config->funcs->atomic_check) ret = config->funcs->atomic_check(state->dev, state);

• /*

• * Reject event generation for when a CRTC is off and stays off. It
  

• * wouldn't be hard to implement this, but userspace has a track record
  

• * of happily burning through 100% cpu (or worse, crash) when the
  

• * display pipe is suspended. To avoid all that fun just reject updates
  

• * that ask for events since likely that indicates a bug in the
  

• * compositors drawing loop. This is consistent with the vblank ioctl
  

• * which also rejects service on a disabled pipe.
  

• */
  

  if (!state->allow_modeset) { for_each_crtc_in_state(state, crtc, crtc_state, i) { if (drm_atomic_crtc_needs_modeset(crtc_state)) {

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c index 110f3db8dd05..8e281a96c35f 100644 --- a/drivers/gpu/drm/drm_atomic_helper.c +++ b/drivers/gpu/drm/drm_atomic_helper.c @@ -2283,6 +2283,14 @@ retry:

Argh! Once again that stupid 'put goto labes at col 0' rule making it impossible to review a patch. Could we *please* change that to put the labels at col 1 instead?

goto fail;

drm_atomic_set_fb_for_plane(plane_state, fb);

• state->allow_modeset = false;
• if (!crtc_state->active) {

• DRM_DEBUG_ATOMIC("[CRTC:%d] disabled, rejecting legacy flip\n",
  

• 		 crtc->base.id);
  

• ret = -EINVAL;
  

• goto fail;
  

• }
• ret = drm_atomic_async_commit(state); if (ret != 0) goto fail;

-- 2.5.1