Re: [RFCv3 2/2] dma-buf: add helpers for sharing attacher constraints with dma-parms

Rob Clark
2015-02-02T20:30:24Z

On Mon, Feb 2, 2015 at 11:54 AM, Daniel Vetter <daniel@ffwll.ch> wrote:
>> My initial thought is for dma-buf to not try to prevent something than
>> an exporter can actually do.. I think the scenario you describe could
>> be handled by two sg-lists, if the exporter was clever enough.
>
> That's already needed, each attachment has it's own sg-list. After all
> there's no array of dma_addr_t in the sg tables, so you can't use one sg
> for more than one mapping. And due to different iommu different devices
> can easily end up with different addresses.

Well, to be fair it may not be explicitly stated, but currently one
should assume the dma_addr_t's in the dmabuf sglist are bogus. With
gpu's that implement per-process/context page tables, I'm not really
sure that there is a sane way to actually do anything else..

BR,
-R