[Intel-gfx] [PATCH] drm/atomic: protect crtc|connector->state with rcu

[Chris Wilson]

On Mon, Mar 20, 2017 at 11:01:59AM +0100, Maarten Lankhorst wrote:
> Op 20-03-17 om 09:59 schreef Daniel Vetter:
> > But my idea was kinda that we'd do the same for probe -> modeset data
> > flows like here for the other way round: Just a bunch of READ_ONCE and
> > maybe lookup the edid with rcu too. That way it's clear to anybody that
> > probe and modeset are entirely not synchronized.
> 
> Though I think it's beneficial to lock them. if it is. I'm not sure there
> are many usecases for parallel modeset vs probe. And if someone does care,
> they can use nonblocking modesets, maybe.
> 
> Legacy userspace probably can't do blocking modeset and probe at the same
> time, so I don't think it will regress.

It can happen - just consider two clients, such as system-logind walking
sysfs. Delaying most modesets would not be an issue, except where the
modeset is being uses to e.g. changes strides before in the middle of a
pageflip sequence.

I would welcome kms_flip flip/set/vblank-vs-probe, and definitely should
add it to legacy-cursor and legacy-plane as well.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre