From mboxrd@z Thu Jan 1 00:00:00 1970 From: Oliver Neukum Subject: Re: USB transfer_buffer allocations on 64bit systems Date: Fri, 9 Apr 2010 22:51:51 +0200 Message-ID: <201004092251.51739.oliver@neukum.org> References: Mime-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-usb-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Alan Stern Cc: Daniel Mack , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Pedro Ribeiro , akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org, Greg KH , alsa-devel-K7yf7f+aM1XWsZ/bQMPhNw@public.gmane.org, linux-usb-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: alsa-devel@alsa-project.org 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-usb" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html