On Tue, Jan 26, 2016 at 01:13:30AM +0530, ankitprasad.r.sharma@xxxxxxxxx wrote:
> From: Ankitprasad Sharma <ankitprasad.r.sharma@xxxxxxxxx>
>
> 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.
>
> v5: Use renamed wrapper function for drm_mm_insert_node_in_range,
> updated barrier positioning (Chris)
>
> v6: Use PAGE_SIZE instead of 4096, use get_pages call before pinning pages
> (Tvrtko)
>
> v7: Fixed the onion (undo operation in reverse order) (Chris)
>
> Testcase: igt/gem_stolen
>
> Signed-off-by: Ankitprasad Sharma <ankitprasad.r.sharma@xxxxxxxxx>
> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_drv.h | 1 +
> drivers/gpu/drm/i915/i915_gem.c | 46 +++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 47 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index c9b8a63..fcaea77 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2892,6 +2892,7 @@ 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 9c751f3..ad70bd3 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -5398,3 +5398,49 @@ 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;
size_t!!!!
> + struct drm_i915_private *i915 = to_i915(obj->base.dev);
I have a different preference for my variable ordering, but meh.
> + struct drm_mm_node node;
> +
> + lockdep_assert_held(&obj->base.dev->struct_mutex);
> + ret = insert_mappable_node(i915, &node, PAGE_SIZE);
> + if (ret)
> + return ret;
> +
> + ret = i915_gem_object_get_pages(obj);
> + if (ret)
> + goto err_remove_node;
> +
> + i915_gem_object_pin_pages(obj);
> + base = io_mapping_map_wc(i915->gtt.mappable, node.start);
> + for (i = 0; i < size/PAGE_SIZE; i++) {
> + i915->gtt.base.insert_page(&i915->gtt.base,
> + i915_gem_object_get_dma_address(obj, i),
> + node.start,
> + I915_CACHE_NONE, 0);
> + wmb();
Again, let's document that these provide explicit barriers with the
insert-page WC into the GGTT versus the WC through the GGTT.
> + memset_io(base, 0, PAGE_SIZE);
> + wmb();
> + }
> +
> + io_mapping_unmap(base);
So whitespace after the loop + unmap, but none before? That's
inconsistent. Either you mean the loop is part of the map-wc critical
section or it is not.
Fix the size_t, and you have my r-b.
-Chris
--
Chris Wilson, Intel Open Source Technology Centre
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