a saner API for allocating DMA addressable pages v2

Christoph Hellwig
2020-09-14T14:49:56Z

Hi all,

this series replaced the DMA_ATTR_NON_CONSISTENT flag to dma_alloc_attrs
with a separate new dma_alloc_pages API, which is available on all
platforms. In addition to cleaning up the convoluted code path, this
ensures that other drivers that have asked for better support for
non-coherent DMA to pages with incurring bounce buffering over can finally
be properly supported.

I'm still a little unsure about the API naming, as alloc_pages sort of
implies a struct page return value, but we return a kernel virtual
address. The other alternative would be to name the API
dma_alloc_noncoherent, but the whole non-coherent naming seems to put
people off. As a follow up I plan to move the implementation of the
DMA_ATTR_NO_KERNEL_MAPPING flag over to this framework as well, given
that is also is a fundamentally non coherent allocation. The replacement
for that flag would then return a struct page, as it is allowed to
actually return pages without a kernel mapping as the name suggested
(although most of the time they will actually have a kernel mapping..)

In addition to the conversions of the existing non-coherent DMA users,
I've also added a patch to convert the firewire ohci driver to use
the new dma_alloc_pages API.

Note that I haven't carried over any Tested-by: tags for the noncoherent
allocation conversions as there was a bit of a patch reshuffle, but the
result should be the same.

The first patch is queued up for 5.9 in the media tree, but included here
for completeness.

A git tree is available here:

git://git.infradead.org/users/hch/misc.git dma_alloc_pages

Gitweb:

http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/dma_alloc_pages

Changes since v1:
- rebased on the latests dma-mapping tree, which merged many of the
cleanups
- fix an argument passing typo in 53c700, caught by sparse
- rename a few macro arguments in 53c700
- pass the right device to the DMA API in the lib82596 drivers
- fix memory ownershiptransfers in sgiseeq
- better document what a page in the direct kernel mapping means
- split into dma_alloc_pages that returns a struct page and is in the
direct mapping vs dma_alloc_noncoherent that can be vmapped
- conver the firewire ohci driver to dma_alloc_pages