Re: [PATCH 13/18] drm/i915: Introduce i915_gem_object_create_stolen()

Ben Widawsky
2012-11-05T16:32:02Z

On Fri, 19 Oct 2012 18:03:19 +0100
Chris Wilson <chris@chris-wilson.co.uk> wrote:

> Allow for the creation of GEM objects backed by stolen memory. As these
> are not backed by ordinary pages, we create a fake dma mapping and store
> the address in the scatterlist rather than obj->pages.
>
> v2: Mark _i915_gem_object_create_stolen() as static, as noticed by Jesse
> Barnes.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>

Deferring on an r-b for now until I understand the point of most of this
patch.

Some comments below however.

> ---
> drivers/gpu/drm/i915/i915_drv.h | 3 +
> drivers/gpu/drm/i915/i915_gem.c | 1 +
> drivers/gpu/drm/i915/i915_gem_stolen.c | 122 ++++++++++++++++++++++++++++++++
> 3 files changed, 126 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 6b893c7..5a0e0cd 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -1526,6 +1526,9 @@ int i915_gem_init_stolen(struct drm_device *dev);
> int i915_gem_stolen_setup_compression(struct drm_device *dev);
> void i915_gem_stolen_cleanup_compression(struct drm_device *dev);
> void i915_gem_cleanup_stolen(struct drm_device *dev);
> +struct drm_i915_gem_object *
> +i915_gem_object_create_stolen(struct drm_device *dev, u32 size);
> +void i915_gem_object_release_stolen(struct drm_i915_gem_object *obj);
>
> /* i915_gem_tiling.c */
> void i915_gem_detect_bit_6_swizzle(struct drm_device *dev);
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index d75c5c3..0349899 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -3857,6 +3857,7 @@ void i915_gem_free_object(struct drm_gem_object *gem_obj)
> obj->pages_pin_count = 0;
> i915_gem_object_put_pages(obj);
> i915_gem_object_free_mmap_offset(obj);
> + i915_gem_object_release_stolen(obj);
>
> BUG_ON(obj->pages);
>
> diff --git a/drivers/gpu/drm/i915/i915_gem_stolen.c b/drivers/gpu/drm/i915/i915_gem_stolen.c
> index 68ef22a..86c4af4 100644
> --- a/drivers/gpu/drm/i915/i915_gem_stolen.c
> +++ b/drivers/gpu/drm/i915/i915_gem_stolen.c
> @@ -204,3 +204,125 @@ int i915_gem_init_stolen(struct drm_device *dev)
>
> return 0;
> }
> +
> +static struct sg_table *
> +i915_pages_create_for_stolen(struct drm_device *dev,
> + u32 offset, u32 size)
> +{
> + struct drm_i915_private *dev_priv = dev->dev_private;
> + struct sg_table *st;
> + struct scatterlist *sg;
> +

BUG_ON(offset + size <= dev_priv->mm.gtt->stolen_size);

> + /* We hide that we have no struct page backing our stolen object
> + * by wrapping the contiguous physical allocation with a fake
> + * dma mapping in a single scatterlist.
> + */
> +
> + st = kmalloc(sizeof(*st), GFP_KERNEL);
> + if (st == NULL)
> + return NULL;
> +
> + if (!sg_alloc_table(st, 1, GFP_KERNEL)) {
> + kfree(st);
> + return NULL;
> + }
> +
> + sg = st->sgl;
> + sg->offset = offset;
> + sg->length = size;
> +
> + sg_dma_address(sg) = dev_priv->mm.stolen_base + offset;
> + sg_dma_len(sg) = size;
> +

Do we want to make stolen_base a dma_addr_t (or at least typecast it)?

> + return st;
> +}
> +
> +static int i915_gem_object_get_pages_stolen(struct drm_i915_gem_object *obj)
> +{
> + BUG();
> + return -EINVAL;
> +}
> +

__noreturn, or maybe just make .get_pages = NULL, and do the check in
the upper layer get_pages?

> +static void i915_gem_object_put_pages_stolen(struct drm_i915_gem_object *obj)
> +{
> + /* Should only be called during free */
> + sg_free_table(obj->pages);
> + kfree(obj->pages);
> +}
> +
> +static const struct drm_i915_gem_object_ops i915_gem_object_stolen_ops = {
> + .get_pages = i915_gem_object_get_pages_stolen,
> + .put_pages = i915_gem_object_put_pages_stolen,
> +};
> +
> +static struct drm_i915_gem_object *
> +_i915_gem_object_create_stolen(struct drm_device *dev,
> + struct drm_mm_node *stolen)
> +{
> + struct drm_i915_gem_object *obj;
> +
> + obj = kzalloc(sizeof(*obj), GFP_KERNEL);
> + if (obj == NULL)
> + return NULL;
> +
> + if (drm_gem_private_object_init(dev, &obj->base, stolen->size))
> + goto cleanup;
> +
> + i915_gem_object_init(obj, &i915_gem_object_stolen_ops);
> +
> + obj->pages = i915_pages_create_for_stolen(dev,
> + stolen->start, stolen->size);
> + if (obj->pages == NULL)
> + goto cleanup;
> +
> + obj->has_dma_mapping = true;
> + obj->pages_pin_count = 1;
> + obj->stolen = stolen;
> +
> + obj->base.write_domain = I915_GEM_DOMAIN_GTT;
> + obj->base.read_domains = I915_GEM_DOMAIN_GTT;
> + obj->cache_level = I915_CACHE_NONE;
> +
> + return obj;
> +
> +cleanup:
> + kfree(obj);
> + return NULL;
> +}
> +
> +struct drm_i915_gem_object *
> +i915_gem_object_create_stolen(struct drm_device *dev, u32 size)
> +{
> + struct drm_i915_private *dev_priv = dev->dev_private;
> + struct drm_i915_gem_object *obj;
> + struct drm_mm_node *stolen;
> +
> + if (dev_priv->mm.stolen_base == 0)
> + return 0;
> +
> + DRM_DEBUG_KMS("creating stolen object: size=%x\n", size);
> + if (size == 0)
> + return NULL;
> +
> + stolen = drm_mm_search_free(&dev_priv->mm.stolen, size, 4096, 0);
> + if (stolen)
> + stolen = drm_mm_get_block(stolen, size, 4096);
> + if (stolen == NULL)
> + return NULL;

Could probably do slightly better here with ERR_PTR(-ENOMEM) but since
we don't do that elsewhere, I guess it doesn't matter.

> +
> + obj = _i915_gem_object_create_stolen(dev, stolen);
> + if (obj)
> + return obj;
> +
> + drm_mm_put_block(stolen);
> + return NULL;

Similarly here maybe use PTR_ERR(obj) and return something meaningful in
_i915_gem_object_create_stolen.

Since just about everything is more or less, ENOMEM, maybe it doesn't
matter.
> +}
> +
> +void
> +i915_gem_object_release_stolen(struct drm_i915_gem_object *obj)
> +{
> + if (obj->stolen) {
> + drm_mm_put_block(obj->stolen);
> + obj->stolen = NULL;
> + }
> +}

--
Ben Widawsky, Intel Open Source Technology Center