Re: [RFC 2/3] USB: core: Add non-coherent buffer allocation helpers

From: Christoph Hellwig
Date: Fri Aug 31 2018 - 01:51:05 EST

On Thu, Aug 30, 2018 at 07:11:35PM -0300, Ezequiel Garcia wrote:
> On Thu, 2018-08-30 at 10:58 -0700, Christoph Hellwig wrote:
> > Please don't introduce new DMA_ATTR_NON_CONSISTENT users, it is
> > a rather horrible interface, and I plan to kill it off rather sooner
> > than later. I plan to post some patches for a better interface
> > that can reuse the normal dma_sync_single_* interfaces for ownership
> > transfers. I can happily include usb in that initial patch set based
> > on your work here if that helps.
> Please do. Until we have proper allocators that go thru the DMA API,
> drivers will have to kmalloc the USB transfer buffers, and have
> streaming mappings. Which in turns mean not using IOMMU or CMA.

dma_map_page will of course use the iommu.