On Thu, Jun 24, 2021 at 11:52:47AM +0200, Christian König wrote:

I've already converted a bunch of the GPU drivers, but there are at least 6 
GPU still needing to be fixed and on top of that comes VA-API and a few 
others.

What are your plans for the DMA mapping subsystem?

Building a new API that allows batched DMA mapping without the scatterlist.
The main input for my use case would be bio_vecs, but I plan to make it
a little flexible, and the output would be a list of [dma_addr,len]
tuples, with the API being flexible enough to just return a single
[dma_addr,len] for the common IOMMU coalescing case.

quoted

Btw, one thing I noticed when looking over the dma-buf instances is that
there is a lot of duplicated code for creating a sg_table from pages,
and then mapping it.  It would be good if we could move toward common
helpers instead of duplicating that all over again.

Can you give an example?

Take a look at the get_sg_table and put_sg_table helpers in udmabuf.
Those would also be useful in armda, i915, tegra, gntdev-dmabuf, mbochs
in one form or another.

Similar for variants that use a contigous regions.