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 <[email protected]> > Cc: Ville Syrjälä <[email protected]> > Signed-off-by: Daniel Vetter <[email protected]> > --- > 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
"compositor's".
> + * 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:
> goto fail;
> drm_atomic_set_fb_for_plane(plane_state, fb);
>
> + state->allow_modeset = false;
Perhaps explain the reason for setting this?
Thierry
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