Re: [PATCH 5/6] drm/amdgpu: add support for exporting VRAM using DMA-buf v2

[Jason Gunthorpe <jgg@ziepe.ca>]

On Wed, Mar 11, 2020 at 02:51:57PM +0100, Christian König wrote:
> +/**
> + * amdgpu_vram_mgr_alloc_sgt - allocate and fill a sg table
> + *
> + * @adev: amdgpu device pointer
> + * @mem: TTM memory object
> + * @dev: the other device
> + * @dir: dma direction
> + * @sgt: resulting sg table
> + *
> + * Allocate and fill a sg table from a VRAM allocation.
> + */
> +int amdgpu_vram_mgr_alloc_sgt(struct amdgpu_device *adev,
> +			      struct ttm_mem_reg *mem,
> +			      struct device *dev,
> +			      enum dma_data_direction dir,
> +			      struct sg_table **sgt)

single ** pointer with an int return is odd, use ERR_PTR?

> +{
> +	struct drm_mm_node *node;
> +	struct scatterlist *sg;
> +	int num_entries = 0;
> +	unsigned int pages;
> +	int i, r;
> +
> +	*sgt = kmalloc(sizeof(*sg), GFP_KERNEL);
> +	if (!*sgt)
> +		return -ENOMEM;
> +
> +	for (pages = mem->num_pages, node = mem->mm_node;
> +	     pages; pages -= node->size, ++node)
> +		++num_entries;
> +
> +	r = sg_alloc_table(*sgt, num_entries, GFP_KERNEL);
> +	if (r)
> +		goto error_free;
> +
> +	for_each_sg((*sgt)->sgl, sg, num_entries, i)
> +		sg->length = 0;
> +
> +	node = mem->mm_node;
> +	for_each_sg((*sgt)->sgl, sg, num_entries, i) {
> +		phys_addr_t phys = (node->start << PAGE_SHIFT) +
> +			adev->gmc.aper_base;
> +		size_t size = node->size << PAGE_SHIFT;
> +		dma_addr_t addr;
> +
> +		++node;
> +		addr = dma_map_resource(dev, phys, size, dir,
> +					DMA_ATTR_SKIP_CPU_SYNC);
> +		r = dma_mapping_error(dev, addr);
> +		if (r)
> +			goto error_unmap;
> +
> +		sg_set_dma_addr(sg, addr, size, 0);

Is it possible that phys will need to have contiguous pages joined
here, or has 'node' already ensured contiguous pages?

Jason
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