> (2) How do I pass a highmem address to the HCDs? The URB structures we use > don't seem particularly well-suited for this.
The urb->transfer_buffer is required to be normal DMA-able memory, following the rules in Documentation/DMA-mapping.txt ... that got cleared up somewhere around the 2.4.5 timeframe, all the HCDs now use the pci_map_single() calls with those buffers. kmalloc() is fine, not vmalloc(), and so on. 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". > (1) Do the USB HCDs support highmem? I seem to recall they do, but I'm not > certain. If URBs can't describe highmem, the HCD's won't support them per se; you'd have to turn highmem to "lowmem" or whatever it's called, and then let the HCDs manage the lowmem-to-dma_addr_t mappings. Alternatively, in 2.5 we might add "highmem" support to USB. Now that I've looked at it a few minutes, I suspect we must -- just to support block devices (usb-storage) fully. Is there more to it than adding page+offset as an alternative way to describe the transfer_buffer? (And making all the "single" mapping calls in the HCDs use page mappings.) - Dave _______________________________________________ [EMAIL PROTECTED] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
