On Sat, 30 Oct 2004, Axel Waggershauser wrote: > I have no sufficient knowledge of the whole scatter-gather method but I > thought version 2 (avoiding copy_to/from_user with sg) would exactly be > the way to go. As far as I understand it, any memory block in user-space > may be at most fragmented into single pages so where would be that > problem with "correct packetization" compared to the suggestion from > Duncan of scattering single pages in kernel-space? Is the problem that > the user-space memory block would have to be page aligned?
(512-byte alignment would be sufficient.) That is the major part of the problem. Another part is that user-space pages may be located in high memory, not directly accessible to the kernel. Not all USB host controllers use DMA, and very few of them can go above the 4 GB cutoff. (However this issue doesn't seem to bother users of the sg and st drivers, and the majority of USB controllers _do_ use DMA.) Alan Stern ------------------------------------------------------- This SF.Net email is sponsored by: Sybase ASE Linux Express Edition - download now for FREE LinuxWorld Reader's Choice Award Winner for best database on Linux. http://ads.osdn.com/?ad_id=5588&alloc_id=12065&op=click _______________________________________________ [EMAIL PROTECTED] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
