On Fri, Feb 9, 2024 at 11:35 PM Michał Mirosław <mirq-linux@xxxxxxxxxxxx> wrote: > > I think it's worth mentioning the cb710 example here, which > > uses a platform device as a child of a PCI device and > > does not assign a DMA mask nor use DMA. > > > > This one will see a change in behavior, meaning that the > > blockdev buffers are no longer bounced. As far as I can > > tell, this is fine because the driver appears to correctly > > use the sg_iter infrastructure for mapping data pages, > > but it would be good to have this confirmed by > > Michał Mirosław because this code path has probably never > > been tested without BLK_BOUNCE_HIGH. > > Hi, this driver doesn't do DMA at all, so having DMA mask set or not > it should be good as long as the CPU can read/write the buffers. The only difference is where the CPU have to read/write the buffers really, before the change those were all guaranteed to be in lowmem (bounced there by the block core), now they can also be in highmem, but sg_miter will deal with it for sure. Yours, Linus Wallej
