On Wed, Nov 19, 2025 at 02:16:57PM +0100, Christian König wrote:
> > +/**
> > + * dma_buf_map - Returns the scatterlist table of the attachment from
> > arrays
> > + * of physical vectors. This funciton is intended for MMIO memory only.
> > + * @attach: [in] attachment whose scatterlist is to be returned
> > + * @provider: [in] p2pdma provider
> > + * @phys_vec: [in] array of physical vectors
> > + * @nr_ranges: [in] number of entries in phys_vec array
> > + * @size: [in] total size of phys_vec
> > + * @dir: [in] direction of DMA transfer
> > + *
> > + * Returns sg_table containing the scatterlist to be returned; returns
> > ERR_PTR
> > + * on error. May return -EINTR if it is interrupted by a signal.
> > + *
> > + * On success, the DMA addresses and lengths in the returned scatterlist
> > are
> > + * PAGE_SIZE aligned.
> > + *
> > + * A mapping must be unmapped by using dma_buf_unmap().
> > + */
> > +struct sg_table *dma_buf_map(struct dma_buf_attachment *attach,
>
> That is clearly not a good name for this function. We already have overloaded
> the term *mapping* with something completely different.
>
> > + struct p2pdma_provider *provider,
> > + struct dma_buf_phys_vec *phys_vec,
> > + size_t nr_ranges, size_t size,
> > + enum dma_data_direction dir)
> > +{
> > + unsigned int nents, mapped_len = 0;
> > + struct dma_buf_dma *dma;
> > + struct scatterlist *sgl;
> > + dma_addr_t addr;
> > + size_t i;
> > + int ret;
> > +
> > + dma_resv_assert_held(attach->dmabuf->resv);
> > +
> > + if (WARN_ON(!attach || !attach->dmabuf || !provider))
> > + /* This function is supposed to work on MMIO memory only */
> > + return ERR_PTR(-EINVAL);
> > +
> > + dma = kzalloc(sizeof(*dma), GFP_KERNEL);
> > + if (!dma)
> > + return ERR_PTR(-ENOMEM);
> > +
> > + switch (pci_p2pdma_map_type(provider, attach->dev)) {
> > + case PCI_P2PDMA_MAP_BUS_ADDR:
> > + /*
> > + * There is no need in IOVA at all for this flow.
> > + */
> > + break;
> > + case PCI_P2PDMA_MAP_THRU_HOST_BRIDGE:
> > + dma->state = kzalloc(sizeof(*dma->state), GFP_KERNEL);
> > + if (!dma->state) {
> > + ret = -ENOMEM;
> > + goto err_free_dma;
> > + }
> > +
> > + dma_iova_try_alloc(attach->dev, dma->state, 0, size);
>
> Oh, that is a clear no-go for the core DMA-buf code.
>
> It's intentionally up to the exporter how to create the DMA
> addresses the importer can work with.
I can't fully understand this remark?
> We could add something like a dma_buf_sg_helper.c or similar and put it in
> there.
Yes, the intention is this function is an "exporter helper" that an
exporter can call if it wants to help generate the scatterlist.
So your "no-go" is just about what file it is in, not anything about
how it works?
Thanks,
Jason
