Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757394Ab0DIVVO (ORCPT ); Fri, 9 Apr 2010 17:21:14 -0400 Received: from iolanthe.rowland.org ([192.131.102.54]:38330 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1755445Ab0DIVVK (ORCPT ); Fri, 9 Apr 2010 17:21:10 -0400 Date: Fri, 9 Apr 2010 17:21:09 -0400 (EDT) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: Oliver Neukum cc: Daniel Mack , , Pedro Ribeiro , , Greg KH , , Subject: Re: USB transfer_buffer allocations on 64bit systems In-Reply-To: <201004092251.51739.oliver@neukum.org> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1612 Lines: 36 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/