Re: [PATCH] drm/i915: Set persistent-mode for SNB framebuffer compression

[Ben Widawsky <ben@bwidawsk.net>]

On Mon, Jul 04, 2011 at 07:18:11PM +0100, Chris Wilson wrote:
> On Mon,  4 Jul 2011 13:35:57 +0100, Chris Wilson <chris@chris-wilson.co.uk> wrote:
> > Persistent mode is intended for use with front-buffer rendering, such as
> > X, where it is necessary to detect writes to the scanout either by the
> > GPU or through the CPU's fence, and recompress the dirty regions on the
> > fly. (By comparison to the back-buffer rendering, the scanout is always
> > recompressed after a page-flip.)
> > 
> > This fixes the missing rendering oft triggered in the past, but easily
> > reproduced by using mutter with sna, for which the current workaround is
> > to disable fbc entirely.
> 
> Hah. Spoke too soon, actually testing it, it seems the fix was due to the
> little buglet in the first patch which had the effect of disabling FBC.
> 
> Oh well, it was a nice idea.
> -Chris

I was looking at the patch you submitted and it made me realize that
surely something must have been missing from my original patch. I'll
play around with fbc a bit more to see if I can find some other magic
bit.

Ben