On Wed, 23 Sep 2020 22:01:25 +0200
Daniel Vetter <daniel.vetter@xxxxxxxx> wrote:
> On Wed, Sep 23, 2020 at 9:17 PM Marius Vlad <marius.vlad@xxxxxxxxxxxxx> wrote:
> >
> > On Wed, Sep 23, 2020 at 05:18:52PM +0200, 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).
...
> > > @@ -1313,6 +1322,26 @@ int drm_atomic_check_only(struct drm_atomic_state *state)
> > > }
> > > }
> > >
> > > + for_each_new_crtc_in_state(state, crtc, old_crtc_state, i)
> > > + affected_crtc |= drm_crtc_mask(crtc);
> > > +
> > > + /*
> > > + * For commits that allow modesets drivers can add other CRTCs to the
> > > + * atomic commit, e.g. when they need to reallocate global resources.
> > > + * This can cause spurious EBUSY, which robs compositors of a very
> > > + * effective sanity check for their drawing loop. Therefor only allow
> > > + * drivers to add unrelated CRTC states for modeset commits.
> > > + *
> > > + * FIXME: Should add affected_crtc mask to the ATOMIC IOCTL as an output
> > > + * so compositors know what's going on.
> > > + */
> > > + if (affected_crtc != requested_crtc) {
> > > + DRM_DEBUG_ATOMIC("driver added CRTC to commit: requested 0x%x, affected 0x%0x\n",
> > > + requested_crtc, affected_crtc);
> > > + WARN(!state->allow_modeset, "adding CRTC not allowed without modesets: requested 0x%x, affected 0x%0x\n",
> > > + requested_crtc, affected_crtc);
> > Previous patch had the warn on state->allow_modeset now is
> > !state->allow_modeset. Is that correct?
>
> We need to fire a warning when allow_modeset is _not_ set. An earlier
> version got that wrong, and yes that would have caused a _ton_ of
> warnings on any fairly new intel platform.
>
> > I haven't followed the entire thread on this matter, but I guess the idea
> > is that somehow the kernel would pass to userspace a CRTC mask of
> > affected_crtc (somehow, we don't know how atm) and with it, userspace
> > can then issue a new commit (this commit blocking) with those?
>
> Either that, or just use that to track all the in-flight drm events.
> Userspace will get events for all the crtc, not just the one it asked
> to update.
Wait, does that happen already? Getting CRTC events for CRTCs userspace
didn't include in the atomic commit?
That could explain why Weston freaks out in
https://gitlab.freedesktop.org/wayland/weston/-/issues/435
Thanks,
pq
> If that's easier to do by re-issuing the commit with the
> full set of crtc, then I guess that's an option. But not required (I
> think at least, would need to test that to make sure).
> -Daniel
>
> > > + }
> > > +
> > > return 0;
> > > }
> > > EXPORT_SYMBOL(drm_atomic_check_only);
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