[Intel-gfx] [PATCH 04/59] drm/i915: Fix for ringbuf space wait in LRC mode

[Chris Wilson]

On Tue, Mar 31, 2015 at 04:50:10PM +0100, Tomas Elf wrote:
> On 19/03/2015 12:30, John.C.Harrison at Intel.com wrote:
> >From: John Harrison <John.C.Harrison at Intel.com>
> >
> >The legacy and LRC code paths have an almost identical procedure for waiting for
> >space in the ring buffer. They both search for a request in the free list that
> >will advance the tail to a point where sufficient space is available. They then
> >wait for that request, retire it and recalculate the free space value.
> >
> >Unfortunately, a bug in the LRC side meant that the resulting free space might
> >not be as large as expected and indeed, might not be sufficient. This is because
> >it was testing against the value of request->tail not request->postfix. Whereas,
> >when a request is retired, ringbuf->tail is updated to req->postfix not
> >req->tail.

req->postfix is garbage, please fix.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre