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

[Matt Roper]

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.


Matt

>  	else
> -- 
> 2.39.2
> 

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