Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757188Ab0DIUvy (ORCPT ); Fri, 9 Apr 2010 16:51:54 -0400 Received: from smtp-out003.kontent.com ([81.88.40.217]:47419 "EHLO smtp-out003.kontent.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756535Ab0DIUvv (ORCPT ); Fri, 9 Apr 2010 16:51:51 -0400 From: Oliver Neukum To: Alan Stern Subject: Re: USB transfer_buffer allocations on 64bit systems Date: Fri, 9 Apr 2010 22:51:51 +0200 User-Agent: KMail/1.12.4 (Linux/2.6.34-rc3-0.1-default; KDE/4.3.5; x86_64; ; ) Cc: Daniel Mack , linux-kernel@vger.kernel.org, Pedro Ribeiro , akpm@linux-foundation.org, Greg KH , alsa-devel@alsa-project.org, linux-usb@vger.kernel.org References: In-Reply-To: MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201004092251.51739.oliver@neukum.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1349 Lines: 29 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. Maybe I understand this wrongly. Which code exactly were you refering to? Regards Oliver -- 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/