[Intel-gfx] [PATCH 3/9] drm/i915: Clearing buffer objects via CPU/GTT

[Tvrtko Ursulin]

Hi,

On 14/12/15 05:46, ankitprasad.r.sharma at intel.com wrote:
> From: Ankitprasad Sharma <ankitprasad.r.sharma at intel.com>
>
> This patch adds support for clearing buffer objects via CPU/GTT. This
> is particularly useful for clearing out the non shmem backed objects.
> Currently intend to use this only for buffers allocated from stolen
> region.
>
> v2: Added kernel doc for i915_gem_clear_object(), corrected/removed
> variable assignments (Tvrtko)
>
> v3: Map object page by page to the gtt if the pinning of the whole object
> to the ggtt fails, Corrected function name (Chris)
>
> v4: Clear the buffer page by page, and not map the whole object in the gtt
> aperture. Use i915 wrapper function in place of drm_mm_insert_node_in_range.
>
> Testcase: igt/gem_stolen
>
> Signed-off-by: Ankitprasad Sharma <ankitprasad.r.sharma at intel.com>
> ---
>   drivers/gpu/drm/i915/i915_drv.h |  1 +
>   drivers/gpu/drm/i915/i915_gem.c | 44 +++++++++++++++++++++++++++++++++++++++++
>   2 files changed, 45 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index a10b866..e195fee 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2897,6 +2897,7 @@ int i915_gem_obj_prepare_shmem_read(struct drm_i915_gem_object *obj,
>   				    int *needs_clflush);
>
>   int __must_check i915_gem_object_get_pages(struct drm_i915_gem_object *obj);
> +int i915_gem_object_clear(struct drm_i915_gem_object *obj);
>
>   static inline int __sg_page_count(struct scatterlist *sg)
>   {
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 46c1e75..e50a91b 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -5293,3 +5293,47 @@ fail:
>   	drm_gem_object_unreference(&obj->base);
>   	return ERR_PTR(ret);
>   }
> +
> +/**
> + * i915_gem_object_clear() - Clear buffer object via CPU/GTT
> + * @obj: Buffer object to be cleared
> + *
> + * Return: 0 - success, non-zero - failure
> + */
> +int i915_gem_object_clear(struct drm_i915_gem_object *obj)
> +{
> +	int ret, i;
> +	char __iomem *base;
> +	size_t size = obj->base.size;
> +	struct drm_i915_private *i915 = to_i915(obj->base.dev);
> +	struct drm_mm_node node;
> +
> +	lockdep_assert_held(&obj->base.dev->struct_mutex);
> +	memset(&node, 0, sizeof(node));
> +	ret = i915_gem_insert_node_in_range(i915, &node, 4096, 0,

Use PAGE_SIZE instead of 4096 since it is used it the for loop below?

> +					    0, i915->gtt.mappable_end);
> +	if (ret)
> +		goto out;
> +
> +	i915_gem_object_pin_pages(obj);

Does it need a call to i915_gem_object_get_pages to work with all 
objects in all scenarios?

> +	base = io_mapping_map_wc(i915->gtt.mappable, node.start);
> +	for (i = 0; i < size/PAGE_SIZE; i++) {
> +		wmb();
> +		i915->gtt.base.insert_page(&i915->gtt.base,
> +					   i915_gem_object_get_dma_address(obj, i),
> +					   node.start,
> +					   I915_CACHE_NONE, 0);
> +		wmb();
> +		memset_io(base, 0, 4096);

Again, maybe also use PAGE_SIZE so it is consistent with the for loop?

> +	}
> +
> +	wmb();
> +	io_mapping_unmap(base);
> +	i915->gtt.base.clear_range(&i915->gtt.base,
> +			node.start, node.size,
> +			true);
> +	drm_mm_remove_node(&node);
> +	i915_gem_object_unpin_pages(obj);
> +out:
> +	return ret;
> +}
>

Regards,

Tvrtko