[Intel-gfx] FBC fixes for review and testing

[Keith Packard]

On Thu,  7 Jul 2011 12:48:05 +0100, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> FBC is currently disabled upstream due a few conflicting requirements
> and questionable benefit. It is also buggy...
> 
> https://bugs.freedesktop.org/show_bug.cgi?id=33487 is the current open
> SNB bug where FBC prevents the screen from being redrawn under a
> compositing WM. At last it appears that we have found the cause and a
> solution, so please do give these patches some testing - you will need
> to pass i915.i915_enable_fbc=1 to override the forced disabling of
> FBC.

This all looks good to me. I've one question though -- enable_fbc needs
to wait for vblank only to make sure it is disabled before turning it
back on right? If so, it seems like we could simply disable FBC
immediately, and then schedule the enable at the next vblank interval
(or even several vblank intervals in the future). Seems like this would
effectively eliminate waiting with the struct_mutex held, which seems
like a nice feature to me.

-- 
keith.packard at intel.com
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