Re: [PATCH 1/3] drm/i915: gen 9 h/w w/a (Wa32bitGeneralStateOffset & Wa32bitInstructionBaseOffset)

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Feb 18, 2015 at 06:19:08PM +0000, Damien Lespiau wrote:
> On Wed, Feb 18, 2015 at 03:16:06PM +0000, Nick Hoath wrote:
> > Signed-off-by: Nick Hoath <nicholas.hoath@intel.com>
> 
> That looks reaaaally drastic and without explanations nor W/A
> documentation that looks wrong.
> 
> Couldn't it be the virtual addresses that need to be on 32 bits? within
> a 64bits PPGTT address space? Also this W/A is listed for BDW/CHV. Right
> now, we have no way of telling what kind of buffer we're being asked to
> relocate into the address space, so there's no way to selectively ensure
> some of those buffers end up with a virtual address that remains in the
> lower 4GB.

I915_GEM_DOMAIN_INSTRUCTION is commonly used for all indirect state by
mesa, so we could restrict the wa to objects with that reloc. Which means
that all the render/texture crap can still be relocated anywhere, which is
the majority.

Of course that means a full audit of mesa/ddx/libva to make sure we don't
break anything. And if there would be breakage we need to make 48bit
address spaces opt-in.

But yeah restricting all objects and then also applying that restriction
to physical objects is _really_ drastic. So please double-check that this
is about physical addresses and not virtual addresses.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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