On Fri, 27 Apr 2018, Christoph Hellwig wrote: > On Sun, Apr 15, 2018 at 11:24:11AM -0400, Alan Stern wrote: > > On Sun, 15 Apr 2018, Christoph Hellwig wrote: > > > > > USB host controllers now must handle highmem, so we can get rid of bounce > > > buffering highmem pages in the block layer. > > > > Sorry, I don't quite understand what you are saying. Do you mean that > > all USB host controllers now magically _do_ handle highmem? Or do you > > mean that if they _don't_ handle highmem, we will not support them any > > more? > > USB controller themselves never cared about highmem, drivers did. For > PIO based controllers they'd have to kmap any address no in the kernel > drirect mapping. > > Nothing in drivers/usb/host or the other diretories related to host > drivers calls page_address (only used in a single gadget) or sg_virt > (only used in a few upper level drivers), which makes me assume > semi-confidently that no USB host driver is not highmem aware these > days.
sg_virt is called in drivers/usb/core/message.c. (Maybe that's what you meant by "upper level drivers".) I'm not sure just how important that usage is. Alan Stern > Greg, does this match your observation as the USB maintainer?
