[Intel-gfx] [PATCH 1/6] drm/i915: Clearing buffer objects via CPU/GTT

[Chris Wilson]

On Wed, Nov 11, 2015 at 04:06:08PM +0530, 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)
> 
> Testcase: igt/gem_stolen
> 
> Signed-off-by: Ankitprasad Sharma <ankitprasad.r.sharma at intel.com>
> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> ---
>  drivers/gpu/drm/i915/i915_drv.h |  1 +
>  drivers/gpu/drm/i915/i915_gem.c | 39 +++++++++++++++++++++++++++++++++++++++
>  2 files changed, 40 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 548a0eb..39b29d3 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_clear_object(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..645b8a0 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -5244,3 +5244,42 @@ 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_clear_object(struct drm_i915_gem_object *obj)
> +{
> +	int ret;
> +	char __iomem *base;
> +	size_t size = obj->base.size;
> +	struct drm_i915_private *dev_priv = 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);
> +	if (ret)
> +		return ret;

Now we have page accessors we can stop thrashing the mappable aperture
for no reason. :)
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre