On 2023-09-26 07:51, Christoph Hellwig wrote:
On Wed, Sep 20, 2023 at 05:54:26PM +0100, Robin Murphy wrote:
As I mentioned before, I think it might make the most sense to make the
whole thing into a "proper" dma_alloc_sgtable() function, which can then be
used with dma_sync_sgtable_*() as dma_alloc_pages() is used with
dma_sync_single_*() (and then dma_alloc_noncontiguous() clearly falls as
the special in-between case).
Why not just use dma_alloc_noncontiguous if the caller wants an sgtable
anyway?
Because we don't need the restriction of the allocation being
DMA-contiguous (and thus having to fall back to physically-contiguous in
the absence of an IOMMU). That's what vb2_dma_contig already does,
whereas IIUC vb2_dma_sg is for devices which can handle genuine
scatter-gather DMA (and so are less likely to have an IOMMU, and more
likely to need the best shot at piecing together large allocations).
Thanks,
Robin.
