Re: [PATCH 21/30] drm/i915: Redirect GTT mappings to the CPU page if cache-coherent

[Eric Anholt <eric@anholt.net>]

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On Tue, 12 Apr 2011 21:31:49 +0100, Chris Wilson <chris@chris-wilson.co.uk> wrote:
> ... or if we will need to perform a cache-flush on the object anyway.
> Unless, of course, we need to use a fence register to perform tiling
> operations during the transfer.

Here's the case I see: I've GTT-map-written a BO (so it hit backing
pages), then that object becomes the framebuffer (PTEs changed to
uncached), then we try to GTT-map-write it some more.  The fake GTT map
skips that.

Also, looks like unrelated change to madvise?

> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_gem.c |   34 ++++++++++++++++++++++++++++++++--
>  1 files changed, 32 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 9d87258..2961f37 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1211,12 +1211,40 @@ int i915_gem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
>  
>  	trace_i915_gem_object_fault(obj, page_offset, true, write);
>  
> -	/* Now bind it into the GTT if needed */
>  	if (!obj->map_and_fenceable) {
>  		ret = i915_gem_object_unbind(obj);
>  		if (ret)
>  			goto unlock;
>  	}
> +
> +	/* If it is unbound or we are currently writing through the CPU
> +	 * domain, continue to do so.
> +	 */
> +	if (obj->tiling_mode == I915_TILING_NONE &&
> +	    (obj->cache_level != I915_CACHE_NONE ||
> +	     obj->base.write_domain == I915_GEM_DOMAIN_CPU)) {
> +		struct page *page;
> +
> +		ret = i915_gem_object_set_to_cpu_domain(obj, write);
> +		if (ret)
> +			goto unlock;
> +
> +		obj->dirty = 1;
> +		obj->fault_mappable = true;
> +		mutex_unlock(&dev->struct_mutex);
> +
> +		page = read_cache_page_gfp(obj->base.filp->f_path.dentry->d_inode->i_mapping,
> +					   page_offset,
> +					   GFP_HIGHUSER | __GFP_RECLAIMABLE);
> +		if (IS_ERR(page)) {
> +			ret = PTR_ERR(page);
> +			goto out;
> +		}
> +
> +		vmf->page = page;
> +		return VM_FAULT_LOCKED;
> +	}
> +
>  	if (!obj->gtt_space) {
>  		ret = i915_gem_object_bind_to_gtt(obj, 0, true);
>  		if (ret)
> @@ -3597,8 +3625,10 @@ i915_gem_madvise_ioctl(struct drm_device *dev, void *data,
>  
>  	/* if the object is no longer bound, discard its backing storage */
>  	if (i915_gem_object_is_purgeable(obj) &&
> -	    obj->gtt_space == NULL)
> +	    obj->gtt_space == NULL) {
> +		i915_gem_release_mmap(obj);
>  		i915_gem_object_truncate(obj);
> +	}
>  
>  	args->retained = obj->madv != __I915_MADV_PURGED;
>  
> -- 
> 1.7.4.1
> 
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