Re: [PATCH 1/6] drm/i915: Clearing buffer objects via CPU/GTT

[Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>]

On Wed, 2015-12-09 at 13:57 +0000, Chris Wilson wrote:
> On Wed, Dec 09, 2015 at 06:16:17PM +0530, ankitprasad.r.sharma@intel.com wrote:
> > From: Ankitprasad Sharma <ankitprasad.r.sharma@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)
> > 
> > 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@intel.com>
> > Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> > ---
> >  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....
> 
Wouldn't it be better, not to use 2 approaches and just do the clearing
using the insert_page function. (not to even try mapping the whole
object) ?

Thanks,
Ankit


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