On Wed, Dec 09, 2015 at 06:16:17PM +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)
>
> 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 | 79 +++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 80 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 548a0eb..8e554d3 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2856,6 +2856,7 @@ 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 9d2e6e3..d57e850 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -5244,3 +5244,82 @@ fail:
> drm_gem_object_unreference(&obj->base);
> return ERR_PTR(ret);
> }
> +
> +/**
> + * i915_gem_clear_object() - 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;
> +
> + WARN_ON(!mutex_is_locked(&obj->base.dev->struct_mutex));
Just lockdep_assert_held.
> + ret = i915_gem_obj_ggtt_pin(obj, 0, PIN_MAPPABLE | PIN_NONBLOCK);
Would be nice to get the PIN_NOFAULT patches in to give preference to
userspace mappings....
> + if (ret) {
> + memset(&node, 0, sizeof(node));
> + ret = drm_mm_insert_node_in_range_generic(&i915->gtt.base.mm,
> + &node, 4096, 0,
> + I915_CACHE_NONE, 0,
> + i915->gtt.mappable_end,
> + DRM_MM_SEARCH_DEFAULT,
> + DRM_MM_CREATE_DEFAULT);
We use this often enough to merit a little helper.
> + if (ret)
> + goto out;
> +
> + i915_gem_object_pin_pages(obj);
> + } else {
> + node.start = i915_gem_obj_ggtt_offset(obj);
> + node.allocated = false;
> + }
> +
> + ret = i915_gem_object_put_fence(obj);
> + if (ret)
> + goto unpin;
You only need to drop the fence when using the whole object GGTT
mmaping.
> +
> + if (node.allocated) {
> + 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();
> + base = ioremap_wc(i915->gtt.mappable_base + node.start, 4096);
> + memset_io(base, 0, 4096);
> + iounmap(base);
> + }
> + } else {
> + /* Get the CPU virtual address of the buffer */
> + base = ioremap_wc(i915->gtt.mappable_base +
> + node.start, size);
You should not use ioremap_wc() as it is easy to exhaust the kernel
address space on 32bit.
If you did a page by page approach for both paths, you could do this with
much less code...
-Chris
--
Chris Wilson, Intel Open Source Technology Centre
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