Re: [RFC] /dev/ioasid uAPI proposal

[Christoph Hellwig]

On Fri, Jun 04, 2021 at 08:58:05AM -0300, Jason Gunthorpe wrote:
> On Fri, Jun 04, 2021 at 09:11:03AM +0800, Jason Wang wrote:
> > > nor do any virtio drivers implement the required platform specific
> > > cache flushing to make no-snoop TLPs work.
> > 
> > I don't get why virtio drivers needs to do that. I think DMA API should hide
> > those arch/platform specific stuffs from us.
> 
> It is not arch/platform stuff. If the device uses no-snoop then a
> very platform specific recovery is required in the device driver.

Well, the proper way to support NO_SNOOP DMA would be to force the
DMA API into supporting the device as if the platform was not DMA
coherent, probably on a per-call basis.  It is just that no one bothered
to actually do the work an people just kept piling hacks over hacks.