[Intel-gfx] [RFC 2/8] drm/i915: Split PTE encode between Gen12 and Meteorlake

[Matt Roper]

On Fri, Jul 28, 2023 at 09:18:36AM +0100, Tvrtko Ursulin wrote:
> 
> On 27/07/2023 23:25, Matt Roper wrote:
> > On Thu, Jul 27, 2023 at 03:54:58PM +0100, Tvrtko Ursulin wrote:
> > > From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> > > 
> > > No need to run extra instructions which will never trigger on platforms
> > > before Meteorlake.
> > > 
> > > Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> > > ---
> > >   drivers/gpu/drm/i915/gt/gen8_ppgtt.c | 26 ++++++++++++++++++++++++++
> > >   1 file changed, 26 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/gt/gen8_ppgtt.c b/drivers/gpu/drm/i915/gt/gen8_ppgtt.c
> > > index c8568e5d1147..862ac1d2de25 100644
> > > --- a/drivers/gpu/drm/i915/gt/gen8_ppgtt.c
> > > +++ b/drivers/gpu/drm/i915/gt/gen8_ppgtt.c
> > > @@ -63,6 +63,30 @@ static u64 gen12_pte_encode(dma_addr_t addr,
> > >   {
> > >   	gen8_pte_t pte = addr | GEN8_PAGE_PRESENT | GEN8_PAGE_RW;
> > > +	if (unlikely(flags & PTE_READ_ONLY))
> > > +		pte &= ~GEN8_PAGE_RW;
> > > +
> > > +	if (flags & PTE_LM)
> > > +		pte |= GEN12_PPGTT_PTE_LM;
> > > +
> > > +	if (pat_index & BIT(0))
> > > +		pte |= GEN12_PPGTT_PTE_PAT0;
> > > +
> > > +	if (pat_index & BIT(1))
> > > +		pte |= GEN12_PPGTT_PTE_PAT1;
> > > +
> > > +	if (pat_index & BIT(2))
> > > +		pte |= GEN12_PPGTT_PTE_PAT2;
> > > +
> > > +	return pte;
> > > +}
> > > +
> > > +static u64 mtl_pte_encode(dma_addr_t addr,
> > > +			  unsigned int pat_index,
> > > +			  u32 flags)
> > > +{
> > > +	gen8_pte_t pte = addr | GEN8_PAGE_PRESENT | GEN8_PAGE_RW;
> > > +
> > 
> > Would it be more readable to start with
> > 
> >          gen8_pte_t pte = gen12_pte_encode(addr, pat_index, flags);
> > 
> > and then |-in only the MTL-specific bit(s) as appropriate?
> > 
> > >   	if (unlikely(flags & PTE_READ_ONLY))
> > >   		pte &= ~GEN8_PAGE_RW;
> > > @@ -995,6 +1019,8 @@ struct i915_ppgtt *gen8_ppgtt_create(struct intel_gt *gt,
> > >   	 */
> > >   	ppgtt->vm.alloc_scratch_dma = alloc_pt_dma;
> > > +	if (GRAPHICS_VER_FULL(gt->i915) >= IP_VER(12, 70))
> > > +		ppgtt->vm.pte_encode = mtl_pte_encode;
> > >   	if (GRAPHICS_VER(gt->i915) >= 12)
> > >   		ppgtt->vm.pte_encode = gen12_pte_encode;
> > 
> > I think you wanted 'else if' here.  Otherwise you clobber the MTL
> > function pointer.
> 
> Doh this was a strong fail.. Yes and yes.. I even had it like you suggest in
> that patch I mentioned to you earlier..
> https://patchwork.freedesktop.org/patch/546013/?series=120341&rev=2.
> 
> Do you have an opinion on that one perhaps?

Yeah, I overlooked that patch before, but it looks good to me.


Matt


> 
> Thanks,
> 
> Tvrtko

-- 
Matt Roper
Graphics Software Engineer
Linux GPU Platform Enablement
Intel Corporation