[Intel-gfx] [PATCH] drm/i915: Wait and retry if there is no space in the aperture mappable area

[Daniel Vetter]

On Fri, Nov 1, 2013 at 7:06 PM, Bloomfield, Jon
<jon.bloomfield at intel.com> wrote:
> Thanks Daniel, sermon noted.
>
> I hadn't twigged that we were pinning buffers to the mapable GTT region which didn't really need to be there. Do we definitely never need to modify or interrogate the hw contexts from the CPU ? What about for debug ?

We can always use direct cpu mappings to the backing storage as long
as we remember to do the coherency dances. Originally we've started to
pin all scanout buffers into the mappable part because that's what our
old userspace expects to be possible. So by default we kinda need to
keep that working.

But even for scanout buffers we could add a new flag somewhere so that
userspace can promise to the kernel to never ever to a gtt mmap (and
then the kernel could also reject any such attempts outright). But
that'd be an extension on top if we notice that the 128M of mappable
for pinned buffers isn't enough. I expect this to happen once 4k
screens get too common ;-)
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch