Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754027AbaGCIlf (ORCPT ); Thu, 3 Jul 2014 04:41:35 -0400 Received: from mx0.aculab.com ([213.249.233.131]:60840 "HELO mx0.aculab.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751031AbaGCIlc (ORCPT ); Thu, 3 Jul 2014 04:41:32 -0400 From: David Laight To: "'Stefan Klug'" , Alan Stern CC: "linux-usb@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: RE: [PATCH][RFC] USB: zerocopy support for usbfs Thread-Topic: [PATCH][RFC] USB: zerocopy support for usbfs Thread-Index: AQHPlpMFL9uP+IUGEEyniU1IREIvbZuOBe9A Date: Thu, 3 Jul 2014 08:40:21 +0000 Message-ID: <063D6719AE5E284EB5DD2968C1650D6D1726BEF0@AcuExch.aculab.com> References: <53B50AB7.2090709@baslerweb.com> In-Reply-To: <53B50AB7.2090709@baslerweb.com> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.202.99.200] Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from base64 to 8bit by mail.home.local id s638fjQj005744 From: Stefan Klug ... > Is there any way to check if the host controller supports arbitrary > alignment? > If I read the xhci spec correctly arbitrary alignment is explicitly > permitted. Not entirely. The xhci spec has a few limits on the alignment of transfer buffer. They seem to be designed to make life difficult for the kernel! 1) Transfer buffers cannot be longer than 64k. 2) Transfer buffers cannot cross 64k address boundaries. 3) The end of a ring segment must occur on a USB packet boundary. The current xhci driver doesn't implement check 3 - which causes certain devices to fail (notable the ax88179_178a usb3 ethernet). David ????{.n?+???????+%?????ݶ??w??{.n?+????{??G?????{ay?ʇڙ?,j??f???h?????????z_??(?階?ݢj"???m??????G????????????&???~???iO???z??v?^?m???? ????????I?