On (20/11/30 09:34), Christoph Hellwig wrote:
>
> > + uvc_urb->pages = dma_alloc_noncontiguous(dma_dev, stream->urb_size,
> > + &uvc_urb->dma,
> > + gfp_flags | __GFP_NOWARN, 0);
> > + if (!uvc_urb->pages)
> > + return false;
> > +
> > + uvc_urb->buffer = vmap(uvc_urb->pages,
> > + PAGE_ALIGN(stream->urb_size) >> PAGE_SHIFT,
> > + VM_DMA_COHERENT, PAGE_KERNEL);
> > + if (!uvc_urb->buffer) {
> > + dma_free_noncontiguous(dma_dev, stream->urb_size,
> > + uvc_urb->pages, uvc_urb->dma);
> > + return false;
> > + }
> > +
> > + if (sg_alloc_table_from_pages(&uvc_urb->sgt, uvc_urb->pages,
> > + PAGE_ALIGN(stream->urb_size) >> PAGE_SHIFT, 0,
> > + stream->urb_size, GFP_KERNEL)) {
> > + vunmap(uvc_urb->buffer);
> > + dma_free_noncontiguous(dma_dev, stream->urb_size,
> > + uvc_urb->pages, uvc_urb->dma);
> > + return false;
> > + }
>
> I wonder if we should lift this into a helper. On the one hand I had
> proliferating struct scatterlist usage, on the other hand it is all over
> the media and drm code anyway, and duplicating this doesn't help anyone.
Not that I have any sound experience in this area, but the helper
probably won't hurt. Do you also plan to add vmap() to that helper
or dma_alloc_noncontiguous()/sg_alloc_table_from_pages() only?
helper()
{
dma_alloc_noncontiguous();
sg_alloc_table_from_pages();
if ((dma_attrs & DMA_ATTR_NO_KERNEL_MAPPING) == 0)
vmap();
}
videobuf2-dma-contig still has to carry around two versions: one that
deals with the noncontig pages and sgt (new API); and the current one.
But if the helper will include fallback to coherent allocations then
this may change, depending on the helper implementation.
-ss
