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SubjectRe: [PATCHv2 8/8] videobuf2: handle non-contiguous DMA allocations
On (21/06/03 13:59), Hans Verkuil wrote:
[[.]
> > static void *vb2_dc_vaddr(struct vb2_buffer *vb, void *buf_priv)
> > {
> > struct vb2_dc_buf *buf = buf_priv;
> > - struct dma_buf_map map;
> > - int ret;
> >
> > - if (!buf->vaddr && buf->db_attach) {
> > - ret = dma_buf_vmap(buf->db_attach->dmabuf, &map);
> > - buf->vaddr = ret ? NULL : map.vaddr;
> > + 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;
> > }
> >
> > + /* Non-coherent memory */
> > + buf->vaddr = dma_vmap_noncontiguous(buf->dev, buf->size, buf->dma_sgt);
> > +
>
> This function can use some comments. What is happening AFAICS is that
> buf->vaddr is either set in vb2_dc_alloc_coherent (unless
> DMA_ATTR_NO_KERNEL_MAPPING was set), it is obtained through dma_buf_vmap()
> if the buffer was attached to a dma_buf, or it is allocated via
> dma_vmap_noncontiguous() for non-coherent memory.

Yeah, it's complicated. Maybe we can make things more symmetrical.

> But this leaves coherent memory with DMA_ATTR_NO_KERNEL_MAPPING set, what
> is vaddr in that case? I think it will call dma_vmap_noncontiguous()
> incorrectly in that case, shouldn't there be a check for !buf->coherent_mem
> before the call to dma_vmap_noncontiguous()?

Thanks a lot for looking into it.

So vb2_dc_vaddr() can look like this:

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;
}

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