From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752114Ab1JQSLW (ORCPT ); Mon, 17 Oct 2011 14:11:22 -0400 Received: from bar.sig21.net ([80.81.252.164]:47710 "EHLO bar.sig21.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751198Ab1JQSLV (ORCPT ); Mon, 17 Oct 2011 14:11:21 -0400 Date: Mon, 17 Oct 2011 20:11:18 +0200 From: Johannes Stezenbach To: Alan Stern Cc: Markus Rechberger , Greg KH , USB list , LKML Subject: Re: [Patch] Increase USBFS Bulk Transfer size Message-ID: <20111017181117.GA17422@sig21.net> References: <20111014224549.GA22810@sig21.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-Spam-21-Score: -1.0 (-) X-Spam-21-Report: No, score=-1.0 required=5.0 tests=ALL_TRUSTED=-1,BAYES_20=-0.001 autolearn=no Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Oct 15, 2011 at 03:04:28PM -0400, Alan Stern wrote: > On Sat, 15 Oct 2011, Johannes Stezenbach wrote: > > > It would make a difference if the > > device violated the spec and sent 188 byte packets. However, the > > spec says a short packet terminates the transfer. But I wonder > > if this is really the case? > > The device does not send short packets. If it did, the 24064-byte > transfers would end early. Re-reading the USB-2.0 standard, a short packet which terminates the transfer is defined by packet_size < wMaxPacketSize, not by packet_size < 512. Thus wMaxPacketSize == 188 (or 2*188) might be possible. There is a comment in linux/drivers/usb/host/ehci-q.c: /* The USB spec says that high speed bulk endpoints * always use 512 byte maxpacket. But some device * vendors decided to ignore that, and MSFT is happy * to help them do so. So now people expect to use * such nonconformant devices with Linux too; sigh. */ Maybe we should look at the descriptors? Johannes