Re: [PATCHv2 8/8] videobuf2: handle non-contiguous DMA allocations

Hi Hans,

On (21/06/17 16:56), Sergey Senozhatsky wrote:
[..]

static void *vb2_dc_vaddr(struct vb2_buffer *vb, void *buf_priv)
{
        struct vb2_dc_buf *buf = buf_priv;

        if (buf->vaddr)
                return buf->vaddr;

        if (buf->db_attach) {
                struct dma_buf_map map;

                if (!dma_buf_vmap(buf->db_attach->dmabuf, &map))
                        buf->vaddr = map.vaddr;

                return buf->vaddr;
        }

        if (!buf->coherent_mem)
                buf->vaddr = dma_vmap_noncontiguous(buf->dev, buf->size,
                                                    buf->dma_sgt);
        return buf->vaddr;
}

And in vb2_dc_alloc functions set vaddr for !DMA_ATTR_NO_KERNEL_MAPPING
in both coherent and non-coherent. So that we probably can have less
branches when ->vaddr is NULL for one type of allocations, and is not
NULL for another.

static int vb2_dc_alloc_coherent(struct vb2_dc_buf *buf)
{
        struct vb2_queue *q = buf->vb->vb2_queue;

        buf->cookie = dma_alloc_attrs(buf->dev,
                                      buf->size,
                                      &buf->dma_addr,
                                      GFP_KERNEL | q->gfp_flags,
                                      buf->attrs);
        if (!buf->cookie)
                return -ENOMEM;

        if (q->dma_attrs & DMA_ATTR_NO_KERNEL_MAPPING)
                return 0;

        buf->vaddr = buf->cookie;
        return 0;
}

static int vb2_dc_alloc_non_coherent(struct vb2_dc_buf *buf)
{
        struct vb2_queue *q = buf->vb->vb2_queue;

        buf->dma_sgt = dma_alloc_noncontiguous(buf->dev,
                                               buf->size,
                                               buf->dma_dir,
                                               GFP_KERNEL | q->gfp_flags,
                                               buf->attrs);
        if (!buf->dma_sgt)
                return -ENOMEM;

        if (q->dma_attrs & DMA_ATTR_NO_KERNEL_MAPPING)
                return 0;

        buf->vaddr = dma_vmap_noncontiguous(buf->dev, buf->size, buf->dma_sgt);
        if (!buf->vaddr) {
                dma_free_noncontiguous(buf->dev, buf->size,
                                       buf->dma_sgt, buf->dma_addr);
                return -ENOMEM;
        }
        return 0;
}

I guess this should address the case when

"after allocating the buffer, the buffer is exported as a dma_buf and
another device calls dma_buf_ops vb2_dc_dmabuf_ops_vmap, which in turn
calls dma_buf_map_set_vaddr(map, buf->vaddr); with a NULL buf->vaddr"

Because ->vaddr will not be NULL now after allocation for both coherent
and non-coherent buffers (modulo DMA_ATTR_NO_KERNEL_MAPPING requests).

What do you think?