On Fri, 9 Apr 2010, Oliver Neukum wrote: > Am Freitag, 9. April 2010 17:15:43 schrieb Alan Stern: > > > > Then usb_submit_urb(urb[i]) will copy the appropriate four bytes to a > > > > bounce buffer and map the bounce buffer. Accesses to the other parts > > > > of xbuf won't violate the cacheline rules, because xbuf isn't mapped > > > > for DMA -- only the bounce buffer is. When urb[i] completes, the > > > > bounce buffer contents will be copied back to the original four bytes > > > > in xbuf. Again, there is no violation of cacheline rules. > > > > > > I think you are assuming that either every or no part of the buffer is mapped > > > for DMA in place. I don't think you can assume that. > > > > Yes I can, because the code that makes this decision is part of > > usbcore and it is under m > > It seems to me that in usbcore you can positively know that a buffer > will be mapped. However if the mapping is not done in usbcore you > cannot know what the HCD driver will do to a buffer, in particular > you don't know whether it will be processed by PIO or mapped for > DMA. The mapping is always done either by usb_buffer_alloc() or by map_urb_for_dma(). Both functions are in usbcore. > Maybe I understand this wrongly. Which code exactly were you refering to? Search for usages of "syncbuf" and "sync_dma" in sound/usb/usbaudio.c. Alan Stern _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
