[Intel-gfx] [PATCH] drm/agp: agp-intel/i915: trim stolen space to 16M

[Zhenyu Wang]

On 2010.03.24 13:28:18 -0700, Jesse Barnes wrote:
> On Wed, 24 Mar 2010 13:06:05 -0700
> Eric Anholt <eric at anholt.net> wrote:
> 
> > On Mon, 22 Mar 2010 11:17:46 -0700, Jesse Barnes <jbarnes at virtuousgeek.org> wrote:
> > > On my SDV, the BIOS allocates 128M of stolen space no matter what
> > > settings I use.  This leaves very little aperture space available (at
> > > least relatively so given my 30" + 24" desktop setup) for mapping
> > > buffers in execbuf.
> > > 
> > > I've been using this patch for awhile to work around the problem, and
> > > think it's a reasonable thing to apply.  We generally only need a small
> > > amount of stolen space for the few things that need contiguous space,
> > > the compressed frame buffer being the biggest.
> > > 
> > > I think I have an idea of how to reclaim the space and give it back to
> > > linux, but I haven't tested that yet; I'll post a follow-up patch on
> > > top of this one when I have it working (basically changing the memory
> > > back to WB using MTRR and/or set_memory_* calls and using memory
> > > hotplug's add_memory() call to return it to the system).
> > > 
> > > Signed-off-by: Jesse Barnes <jbarnes at virtuousgeek.org>
> > 
> > I love the idea!  The interactions between the two modules are sure
> > ugly, though -- like the duplication of i915_probe_agp().  That's part
> > of why I've wished we would just pull GTT setup into the DRM and leave
> > intel-agp to rot for non-KMS support that actually uses the agpgart
> > interfaces.
> 
> Agreed.  I briefly looked at cleaning that up too, but it seemed pretty
> invasive to the AGP and DRM code, so I left it for another day.

yeah, another benefit I can think of is that if we want to do PPGTT support
in future, we don't have to hook up possible new APIs in AGP to serve DRM,
which is really inconvenient.

> 
> > Given that the DRM wants a variable amount of the stolen memory for its
> > purposes, it seems like we need for the DRM to be able to tell AGP how
> > much it should give back.  Probably easiest would be for DRM to just do
> > that by binding things in at lower addresses if it feels like, and AGP
> > should just do whatever the DRM says without checking if the DRM's
> > offset happened to be in stolen.
> 
> Yeah that would probably be better, and would be easier after reworking
> things.
> 

-- 
Open Source Technology Center, Intel ltd.

$gpg --keyserver wwwkeys.pgp.net --recv-keys 4D781827
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