[Intel-gfx] [PATCH] drm/i915: add a LLC feature flag in device description

[Eric Anholt]

On Tue, 13 Dec 2011 17:09:37 +0100, Daniel Vetter <daniel at ffwll.ch> wrote:
> On Tue, Dec 13, 2011 at 11:05:15AM -0200, Eugeni Dodonov wrote:
> > From: Eugeni Dodonov <eugeni.dodonov at intel.com>
> > 
> > LLC is not SNB-specific, so we should check for it in a more generic way.
> > 
> > v2: export LLC support status via debugfs and DRM GETPARAM.
> > 
> > Signed-off-by: Eugeni Dodonov <eugeni.dodonov at intel.com>
> 
> Nice patch and would get an r-b from me safe for the new GETPARAM. I
> really think we need to export this on a per-bo basis (and with the caveat
> that the kernel is free to change the caching on every ioctl that uses
> it). I.e. without forcing userspace to check the caching bits before any
> bo access I fear that we won't be able to change the kernel's behaviour in
> this area, which surely results in backwards-compat hell when the first
> w/a that needs such changes comes around. Hence in its current from
> 
> Nacked-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> 
> So please drop the GETPARAM. For the per-bo get_cache_flags ioctl there's
> already a patch by Ben floating around.

The way the getparam would be useful is that right now we're taking some
different paths for performance reasons in Mesa on gen6, assuming that
LLC is present.  Knowing whether or not we expect BOs in general to be
LLC for performance would be nice for that -- without that, I'll just
make assumptions based on chipset generation.
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