On Tue, Jan 01 2002, David Brownell wrote: > > > Not that I've seen a writeup about highmem (linux/Documentation > > > doesn't seem to have one anyway) but if I infer correctly from that > > > DMA-mapping.txt writeup, URBs don't support it because there's no way > > > to specify buffers as a "struct page *" or an array of "struct > > > scatterlist". That's the only way that document identifies to access > > > "highmem memory". > > > > What kind of mapping does URBs require? A virtual mapping? > > Each URB points to one transfer buffer, address plus length, where > the USB device drivers directly read/write those addresses. The > requirement for drivers is that the transfer buffers can be passed to > pci_map_single() calls by the Host Controller Drivers (HCDs). The > device drivers, and URBs, don't expose such mappings, they only > require that they can be created/destroyed.
.. which is the requirement that you want to change to use pci_map_page or pci_map_sg > I'd be inclined to say transfer buffers must not be "virtual" mappings, > but since terminology can differ I'll let you draw your conclusion. They must not be, currently they are. > Standard HC hardware (EHCI, OHCI, UHCI) can use 32bit addresses > for their PCI DMA. EHCI can also, in some implementations, handle 64bit > addresses. Good > > > (And making all the "single" mapping calls in the HCDs use page > > > mappings.) > > > > exactly > > So you're saying that pci_map_page() is not necessary? And that > highmem buffers (page+offset, or scatterlist thereof) can be turned > into the form needed by URBs using some other mechanism? Sorry if I wasn't clear, no that's not what I meant. See above. pci_map_single requires a virtual mapping so it simply cannot support highmem. -- Jens Axboe _______________________________________________ [EMAIL PROTECTED] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
