On Mon, Sep 18, 2017 at 9:20 AM, Chad Versace <chadvers...@chromium.org> wrote:
> On Thu 14 Sep 2017, Eric Anholt wrote: > > Jason Ekstrand <ja...@jlekstrand.net> writes: > > > > > The setTexBuffer2 hook from GLX is used to implement glxBindTexImageEXT > > > which has tighter restrictions than just "it's shared". In particular, > > > it says that any rendering to the image while it is bound causes the > > > contents to become undefined. This means that we can do whatever aux > > > tracking we want between glxBindTexImageEXT and glxReleaseTexImageEXT > so > > > long as we always transition from external in Bind and to external in > > > Release. > > > > The intent of the spec was to get at the hard-to-define "you get pixels > > at least as new as the outstanding X11 rendering when you called > > glxBindTexImageEXT(), but if X11 keeps on rendering to the thing then > > you may get newer pixels, too." With your CCS plan and X11 rendering in > > parallel with you GL texturing from the X11 pixmap, will we always see > > either old or new pixels but not anything else? > That gets interesting... Yes, reading and writing to a CCS image at the same time is problematic. However, the spec does say "undefined" and not "either new or old pixels". :-) I'm not sure how this translates into the real world though. > We have bigger problems if X11 today renders to any surface that has > been externally shared with I915_FORMAT_MOD_Y_TILED_CCS. If I ran > git-grep correctly, then xf86-video-intel nor xf86-video-modesetting is > unaware of modifiers and hence unaware of CCS aux state. > you're not grepping the right branches. :-) We do have code floating around that makes modesetting modifiers-aware. It's not aware of what the modifiers mean other than that multi-planar modifiers have racing trouble and it avoids using them for front-buffer rendering. That said, I've run a variety of examples, and I have yet to see any corruption issues. > So, with respect to reviewing this patch, I think it's safe to assume > that X11 never renders to a CCS-enabled surface, and that this patch is > the correct fix. If X11 does render to CCS-enabled surfaces, then we > have more invasive problems that need fixing. > Yes. In any case, I think the old code was decidedly wrong in the face of modifiers. > Reviewed-by: Chad Versace <chadvers...@chromium.org> >
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