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

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