[Intel-gfx] [PATCH 1/2] drm/i915/bdw: Use scratch page table for GEN8 PPGTT

[Ben Widawsky]

Way more coming in terms of sharing code. If you feel like looking
into the future:
http://cgit.freedesktop.org/~bwidawsk/drm-intel/log/?h=dynamic_pt_alloc

I've hoped, and continue to hope to kill insert/clear_entires
entirely. Still debugging some gen7 crap though for now.

On Tue, Mar 11, 2014 at 9:46 AM, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> On Tue, Mar 11, 2014 at 09:39:30AM -0700, Ben Widawsky wrote:
>> On Tue, Mar 11, 2014 at 5:24 AM, Chris Wilson <chris at chris-wilson.co.uk> wrote:
>> > On Sat, Mar 08, 2014 at 11:59:42AM -0800, Ben Widawsky wrote:
>> >> On Sat, Mar 08, 2014 at 11:58:16AM -0800, Ben Widawsky wrote:
>> >> > I'm not clear if the hardware is still subject to the same prefetching
>> >> > issues that made us use a scratch page in the first place. In either
>> >> > case, we're using garbage with the current code (we will end up using
>> >> > offset 0).
>> >> >
>> >> > This may be the cause of our current gem_cpu_reloc regression with
>> >> > PPGTT. I cannot test it at the moment.
>> >> >
>> >>
>> >> Wait NVM... that wasn't gen8. I can't associate this one with a bug.
>> >
>> > Yeah, this doesn't appear to achieve anything. ppgtt->base.scratch is
>> > only used by ppgtt->base.clear_range() and there is no caller between
>> > i915_gem_init_ppgtt() and ppgtt->base.scratch initialisation in
>> > gen6_ppgtt_init().
>>
>>
>> Still the right thing to do for gen8 though, right?
>
> Likewise vm->scratch.addr is only used by gen8_ppgtt_clear_range()...
> Except that it is never initialized to point to the scratch page in
> gen8_ppgtt_init(). So yes, wrt gen8 it is the right thing to do. There
> is more common code you could refactor if you so desired though...
>
> My bad for not realising this was to fix the gen8 bug, I was looking for
> something broken in the gen6 init sequence. So,
> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
> -Chris
>
> --
> Chris Wilson, Intel Open Source Technology Centre