On Wed, 2015-12-09 at 13:26 +0000, Dave Gordon wrote:
> On 09/12/15 12:46, 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));
> > + ret = i915_gem_obj_ggtt_pin(obj, 0, PIN_MAPPABLE | PIN_NONBLOCK);
> > + 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);
> > + 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;
> > +
> > + 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);
> > + if (base == NULL) {
> > + DRM_ERROR("Mapping of gem object to CPU failed!\n");
> > + ret = -ENOSPC;
> > + goto unpin;
> > + }
> > +
> > + memset_io(base, 0, size);
> > + iounmap(base);
> > + }
> > +unpin:
> > + if (node.allocated) {
> > + wmb();
> > + i915->gtt.base.clear_range(&i915->gtt.base,
> > + node.start, node.size,
> > + true);
> > + drm_mm_remove_node(&node);
> > + i915_gem_object_unpin_pages(obj);
> > + }
> > + else {
> > + i915_gem_object_ggtt_unpin(obj);
> > + }
> > +out:
> > + return ret;
> > +}
>
> This is effectively two functions interleaved, as shown by the repeated
> if (node.allocated) tests. Would it not be clearer to have the mainline
> function deal only with the GTT-pinned case, and a separate function for
> the page-by-page version, called as a fallback if pinning fails?
>
> 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);
>
> WARN_ON(!mutex_is_locked(&obj->base.dev->struct_mutex));
> ret = i915_gem_obj_ggtt_pin(obj, 0, PIN_MAPPABLE|PIN_NONBLOCK);
> if (ret)
> return __i915_obj_clear_by_pages(...);
>
> ... mainline (fast) code here ...
>
> return ret;
> }
>
> static int __i915_obj_clear_by_pages(...);
> {
> ... complicated page-by-page fallback code here ...
> }
>
This is good to separate the page-by-page path to not make the code
messy, Also I kind of liked Chris' suggestion to not use ioremap_wc() as
it could easily exhaust kernel space.
To make it less messy and more robust, I would prefer to use only the
page-by-page path (no need to even try mapping the full object), with
io_mapping_map_wc()
Thanks,
Ankit
>
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