Re: [PATCH v6 1/2] drm/i915/gt: introduce vm->scratch_range callback

["Das, Nirmoy" <nirmoy.das@xxxxxxxxxxxxxxx>]

On 3/10/2023 10:23 AM, Andrzej Hajda wrote:
> The callback will be responsible for setting scratch page PTEs for
> specified range. In contrast to clear_range it cannot be optimized to nop.
> It will be used by code adding guard pages.
>
> Signed-off-by: Andrzej Hajda <andrzej.hajda@xxxxxxxxx>
Reviewed-by: Nirmoy Das <nirmoy.das@xxxxxxxxx>
> ---
>   drivers/gpu/drm/i915/gt/intel_ggtt.c      | 23 +++++++++++++++++++++++
>   drivers/gpu/drm/i915/gt/intel_ggtt_gmch.c |  1 +
>   drivers/gpu/drm/i915/gt/intel_gtt.h       |  2 ++
>   3 files changed, 26 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_ggtt.c b/drivers/gpu/drm/i915/gt/intel_ggtt.c
> index 842e69c7b21e49..38e6f0b207fe0c 100644
> --- a/drivers/gpu/drm/i915/gt/intel_ggtt.c
> +++ b/drivers/gpu/drm/i915/gt/intel_ggtt.c
> @@ -291,6 +291,27 @@ static void gen8_ggtt_insert_entries(struct i915_address_space *vm,
>   	ggtt->invalidate(ggtt);
>   }
>   
> +static void gen8_ggtt_clear_range(struct i915_address_space *vm,
> +				  u64 start, u64 length)
> +{
> +	struct i915_ggtt *ggtt = i915_vm_to_ggtt(vm);
> +	unsigned int first_entry = start / I915_GTT_PAGE_SIZE;
> +	unsigned int num_entries = length / I915_GTT_PAGE_SIZE;
> +	const gen8_pte_t scratch_pte = vm->scratch[0]->encode;
> +	gen8_pte_t __iomem *gtt_base =
> +		(gen8_pte_t __iomem *)ggtt->gsm + first_entry;
> +	const int max_entries = ggtt_total_entries(ggtt) - first_entry;
> +	int i;
> +
> +	if (WARN(num_entries > max_entries,
> +		"First entry = %d; Num entries = %d (max=%d)\n",
> +		first_entry, num_entries, max_entries))
> +		num_entries = max_entries;
> +
> +	for (i = 0; i < num_entries; i++)
> +		gen8_set_pte(&gtt_base[i], scratch_pte);
> +}
> +
>   static void gen6_ggtt_insert_page(struct i915_address_space *vm,
>   				  dma_addr_t addr,
>   				  u64 offset,
> @@ -919,6 +940,7 @@ static int gen8_gmch_probe(struct i915_ggtt *ggtt)
>   	ggtt->vm.cleanup = gen6_gmch_remove;
>   	ggtt->vm.insert_page = gen8_ggtt_insert_page;
>   	ggtt->vm.clear_range = nop_clear_range;
> +	ggtt->vm.scratch_range = gen8_ggtt_clear_range;
>   
>   	ggtt->vm.insert_entries = gen8_ggtt_insert_entries;
>   
> @@ -1082,6 +1104,7 @@ static int gen6_gmch_probe(struct i915_ggtt *ggtt)
>   	ggtt->vm.clear_range = nop_clear_range;
>   	if (!HAS_FULL_PPGTT(i915))
>   		ggtt->vm.clear_range = gen6_ggtt_clear_range;
> +	ggtt->vm.scratch_range = gen6_ggtt_clear_range;
>   	ggtt->vm.insert_page = gen6_ggtt_insert_page;
>   	ggtt->vm.insert_entries = gen6_ggtt_insert_entries;
>   	ggtt->vm.cleanup = gen6_gmch_remove;
> diff --git a/drivers/gpu/drm/i915/gt/intel_ggtt_gmch.c b/drivers/gpu/drm/i915/gt/intel_ggtt_gmch.c
> index 77c793812eb46a..d6a74ae2527bd9 100644
> --- a/drivers/gpu/drm/i915/gt/intel_ggtt_gmch.c
> +++ b/drivers/gpu/drm/i915/gt/intel_ggtt_gmch.c
> @@ -102,6 +102,7 @@ int intel_ggtt_gmch_probe(struct i915_ggtt *ggtt)
>   	ggtt->vm.insert_page = gmch_ggtt_insert_page;
>   	ggtt->vm.insert_entries = gmch_ggtt_insert_entries;
>   	ggtt->vm.clear_range = gmch_ggtt_clear_range;
> +	ggtt->vm.scratch_range = gmch_ggtt_clear_range;
>   	ggtt->vm.cleanup = gmch_ggtt_remove;
>   
>   	ggtt->invalidate = gmch_ggtt_invalidate;
> diff --git a/drivers/gpu/drm/i915/gt/intel_gtt.h b/drivers/gpu/drm/i915/gt/intel_gtt.h
> index 5a775310d3fcb5..69ce55f517f567 100644
> --- a/drivers/gpu/drm/i915/gt/intel_gtt.h
> +++ b/drivers/gpu/drm/i915/gt/intel_gtt.h
> @@ -298,6 +298,8 @@ struct i915_address_space {
>   				  u64 start, u64 length);
>   	void (*clear_range)(struct i915_address_space *vm,
>   			    u64 start, u64 length);
> +	void (*scratch_range)(struct i915_address_space *vm,
> +			      u64 start, u64 length);
>   	void (*insert_page)(struct i915_address_space *vm,
>   			    dma_addr_t addr,
>   			    u64 offset,