On Tue, Feb 25, 2020 at 12:50:24PM +0100, Daniel Vetter wrote: > When doing an atomic modeset with ALLOW_MODESET drivers are allowed to > pull in arbitrary other resources, including CRTCs (e.g. when > reconfiguring global resources). > > But in nonblocking mode userspace has then no idea this happened, > which can lead to spurious EBUSY calls, both: > - when that other CRTC is currently busy doing a page_flip the > ALLOW_MODESET commit can fail with an EBUSY > - on the other CRTC a normal atomic flip can fail with EBUSY because > of the additional commit inserted by the kernel without userspace's > knowledge > > For blocking commits this isn't a problem, because everyone else will > just block until all the CRTC are reconfigured. Only thing userspace > can notice is the dropped frames without any reason for why frames got > dropped. > > Consensus is that we need new uapi to handle this properly, but no one > has any idea what exactly the new uapi should look like. As a stop-gap > plug this problem by demoting nonblocking commits which might cause > issues by including CRTCs not in the original request to blocking > commits. > > v2: Add comments and a WARN_ON to enforce this only when allowed - we > don't want to silently convert page flips into blocking plane updates > just because the driver is buggy. > > v3: Fix inverted WARN_ON (Pekka). > > References: https://lists.freedesktop.org/archives/dri-devel/2018-July/182281.html > Bugzilla: https://gitlab.freedesktop.org/wayland/weston/issues/24#note_9568 > Cc: Daniel Stone <daniel@xxxxxxxxxxxxx> > Cc: Pekka Paalanen <pekka.paalanen@xxxxxxxxxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx > Reviewed-by: Daniel Stone <daniels@xxxxxxxxxxxxx> > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx> > --- > drivers/gpu/drm/drm_atomic.c | 34 +++++++++++++++++++++++++++++++--- > 1 file changed, 31 insertions(+), 3 deletions(-) > > diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c > index 9ccfbf213d72..4c035abf98b8 100644 > --- a/drivers/gpu/drm/drm_atomic.c > +++ b/drivers/gpu/drm/drm_atomic.c > @@ -1362,15 +1362,43 @@ EXPORT_SYMBOL(drm_atomic_commit); > int drm_atomic_nonblocking_commit(struct drm_atomic_state *state) > { > struct drm_mode_config *config = &state->dev->mode_config; > - int ret; > + unsigned requested_crtc = 0; > + unsigned affected_crtc = 0; > + struct drm_crtc *crtc; > + struct drm_crtc_state *crtc_state; > + bool nonblocking = true; > + int ret, i; > + > + /* > + * For commits that allow modesets drivers can add other CRTCs to the > + * atomic commit, e.g. when they need to reallocate global resources. > + * > + * But when userspace also requests a nonblocking commit then userspace > + * cannot know that the commit affects other CRTCs, which can result in > + * spurious EBUSY failures. Until we have better uapi plug this by > + * demoting such commits to blocking mode. > + */ > + for_each_new_crtc_in_state(state, crtc, crtc_state, i) > + requested_crtc |= drm_crtc_mask(crtc); > > ret = drm_atomic_check_only(state); > if (ret) > return ret; > > - DRM_DEBUG_ATOMIC("committing %p nonblocking\n", state); > + for_each_new_crtc_in_state(state, crtc, crtc_state, i) > + affected_crtc |= drm_crtc_mask(crtc); > + > + if (affected_crtc != requested_crtc) { > + /* adding other CRTC is only allowed for modeset commits */ > + WARN_ON(!state->allow_modeset); Not sure that's really true. What if the driver needs to eg. redistribute FIFO space or something between the pipes? Or do we expect drivers to now examine state->allow_modeset to figure out if they're allowed to do certain things? > + > + DRM_DEBUG_ATOMIC("demoting %p to blocking mode to avoid EBUSY\n", state); > + nonblocking = false; > + } else { > + DRM_DEBUG_ATOMIC("committing %p nonblocking\n", state); > + } > > - return config->funcs->atomic_commit(state->dev, state, true); > + return config->funcs->atomic_commit(state->dev, state, nonblocking); > } > EXPORT_SYMBOL(drm_atomic_nonblocking_commit); > > -- > 2.24.1 > > _______________________________________________ > Intel-gfx mailing list > Intel-gfx@xxxxxxxxxxxxxxxxxxxxx > https://lists.freedesktop.org/mailman/listinfo/intel-gfx -- Ville Syrjälä Intel
