[Intel-gfx] [PATCH 2/4] drm/i915: prevent tiling changes on framebuffer backing storage

Daniel Vetter daniel at ffwll.ch
Thu Oct 10 00:09:48 CEST 2013

On Thu, Oct 10, 2013 at 12:02:17AM +0200, Daniel Vetter wrote:
> On Wed, Oct 09, 2013 at 10:29:39PM +0100, Chris Wilson wrote:
> > On Wed, Oct 09, 2013 at 09:23:52PM +0200, Daniel Vetter wrote:
> > > Assuming that all framebuffer related metadata is invariant simplifies
> > > our userspace input data checking. And current userspace always first
> > > updates the tiling of an object before creating a framebuffer with it.
> > 
> > Userspace already changes the tiling layout whilst keeping the fb id.
> How exactly does that work? You can't really change the fb pitch without
> creating a new one ... That leaves switching from tiled to untiled and
> back I think.

Meh, didn't read sna carefully enough. On a second read we only seem to
have the code added

commit 0dd20381364aabede2e1306945abe21d57c1d7b4
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Sun Sep 29 11:19:46 2013 +0100

    sna: Resize an existing framebuffer if possible

That seems to just be for the cache, should be able to cope with failures
and we can fix it by moving the rmfb up before the set_tiling. It's also
only 2 weeks old.

So if there's nothing else I've missed I strongly vote to break the
pre-release over saner intefaces - allowing tiling to change kinda wreaks
a bit havoc with out in-kernel checks ...
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch

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