Re: [Intel-gfx] [PATCH] drm/i915/gtt: add some flushing for the 64K GTT path

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Matthew Auld <matthew.auld@intel.com> writes:

> If we need to mark the PDE as operating in 64K GTT mode, we should be
> paranoid and flush the extra writes, like we already do for the PTEs. On
> some platforms the clflush can apparently add the just the right amount
> of magical delay to force the GPU to see the updated entry.
>
> Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>

Makes sense to follow the same pattern as the other writes.

Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>

> ---
>  drivers/gpu/drm/i915/gt/gen8_ppgtt.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/gt/gen8_ppgtt.c b/drivers/gpu/drm/i915/gt/gen8_ppgtt.c
> index 6e0e52eeb87a..6a5af995f5b1 100644
> --- a/drivers/gpu/drm/i915/gt/gen8_ppgtt.c
> +++ b/drivers/gpu/drm/i915/gt/gen8_ppgtt.c
> @@ -548,6 +548,7 @@ static void gen8_ppgtt_insert_huge(struct i915_vma *vma,
>  					      I915_GTT_PAGE_SIZE_2M)))) {
>  			vaddr = px_vaddr(pd);
>  			vaddr[maybe_64K] |= GEN8_PDE_IPS_64K;
> +			clflush_cache_range(vaddr, PAGE_SIZE);
>  			page_size = I915_GTT_PAGE_SIZE_64K;
>  
>  			/*
> @@ -568,6 +569,7 @@ static void gen8_ppgtt_insert_huge(struct i915_vma *vma,
>  				for (i = 1; i < index; i += 16)
>  					memset64(vaddr + i, encode, 15);
>  
> +				clflush_cache_range(vaddr, PAGE_SIZE);
>  			}
>  		}
>  
> -- 
> 2.26.3