Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762754AbYFWTHb (ORCPT ); Mon, 23 Jun 2008 15:07:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755371AbYFWTHV (ORCPT ); Mon, 23 Jun 2008 15:07:21 -0400 Received: from cluster-d.mailcontrol.com ([217.69.20.190]:57300 "EHLO cluster-d.mailcontrol.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755261AbYFWTHT (ORCPT ); Mon, 23 Jun 2008 15:07:19 -0400 Message-ID: <485FF44C.4010600@csr.com> Date: Mon, 23 Jun 2008 20:06:52 +0100 From: David Vrabel User-Agent: Thunderbird 2.0.0.14 (X11/20080505) MIME-Version: 1.0 To: Alan Stern CC: Kernel development list , AntonioLin , linux-usb@vger.kernel.org, "Perez-Gonzalez, Inaky" Subject: Re: Scatter-gather list constraints References: In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-OriginalArrivalTime: 23 Jun 2008 19:06:52.0365 (UTC) FILETIME=[4BB4DFD0:01C8D564] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1487 Lines: 35 Alan Stern wrote: > On Mon, 23 Jun 2008, David Vrabel wrote: > >> Note that this 1024 byte multiple is for one particular WUSB mass >> storage device. The WUSB standard permits max packet sizes of up 3584 >> (in multiples of 512), but I suspect WUSB mass storage devices will only >> use 512, 1024, or 2048. >> >> For a solution, we may be able to do something if the HWA host >> controller is passed a single URB with an s-g list (rather than one URB >> per s-g list entry) and was careful about how it segmented the URB into >> transfers to the rpipe. > > That would be ideal. However there is no way to pass an S-G list along > with an URB; there's no field for it in the data structure. And none > of the existing host controller drivers support such a thing. > > I suppose we could add a field to struct urb and add a flag indicating > whether the controller driver supports S-G lists. This is what I was thinking. Can the number of entries in a sg list be limited? e.g., if the hardware only had support for say, 64 entries? David -- David Vrabel, Senior Software Engineer, Drivers CSR, Churchill House, Cambridge Business Park, Tel: +44 (0)1223 692562 Cowley Road, Cambridge, CB4 0WZ http://www.csr.com/ -- 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/