[Intel-gfx] [PATCH] drm/i915: Implement dma-buf mmap() on systems with LLC

[Daniel Vetter]

On Mon, Feb 24, 2014 at 07:50:49PM +0000, Rob Bradford wrote:
> From: Rob Bradford <rob at linux.intel.com>
> 
> The LLC check echoes the check made by i915_gem_fault() which will
> handle the mapping the pages through the GTT.
> 
> The aim is that this is functionally equivalent to using the
> I915_GEM_MMAP_GTT ioctl and then mmaping using the offset returned.
> 
> Signed-off-by: Rob Bradford <rob at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/i915_gem_dmabuf.c | 20 +++++++++++++++++++-
>  1 file changed, 19 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/i915_gem_dmabuf.c
> index 9bb533e..55ff592 100644
> --- a/drivers/gpu/drm/i915/i915_gem_dmabuf.c
> +++ b/drivers/gpu/drm/i915/i915_gem_dmabuf.c
> @@ -197,7 +197,25 @@ static void i915_gem_dmabuf_kunmap(struct dma_buf *dma_buf, unsigned long page_n
>  
>  static int i915_gem_dmabuf_mmap(struct dma_buf *dma_buf, struct vm_area_struct *vma)
>  {
> -	return -EINVAL;
> +	struct drm_i915_gem_object *obj = dma_buf_to_obj(dma_buf);
> +	struct drm_device *dev = obj->base.dev;
> +	int ret;
> +
> +	if (!HAS_LLC(dev))
> +		return -EINVAL;
> +
> +	ret = i915_mutex_lock_interruptible(dev);
> +	if (ret)
> +		goto unlock;
> +
> +	ret = drm_gem_mmap_obj(&obj->base, vma_pages(vma) << PAGE_SHIFT, vma);

The gtt memory mapping you're forwarding here to is actually always
coherent, so the LLC test is redundant. The only issue is if you try to
gtt mmap a coherent BO on pre-snb, iirc that can hang.

Another thing is the pte shootdown. I think to make that work you need to
frob the vma -> mapping association a bit so that unmap_mapping_range
works correctly. A testcase which dma-buf mmaps more data than we have cpu
accessible gtt space should easily hit this.

Which brings up the last bit: This needs a prime_mmap testcase in igt ...

Cheers, Daniel

> +
> +	if (ret)
> +		goto unlock;
> +
> +unlock:
> +	mutex_unlock(&dev->struct_mutex);
> +	return ret;
>  }
>  
>  static int i915_gem_begin_cpu_access(struct dma_buf *dma_buf, size_t start, size_t length, enum dma_data_direction direction)
> -- 
> 1.8.3.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch