From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 102A1C433E9 for ; Fri, 22 Jan 2021 17:21:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D0DE923433 for ; Fri, 22 Jan 2021 17:21:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729446AbhAVQzw (ORCPT ); Fri, 22 Jan 2021 11:55:52 -0500 Received: from netrider.rowland.org ([192.131.102.5]:41021 "HELO netrider.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1729587AbhAVQVC (ORCPT ); Fri, 22 Jan 2021 11:21:02 -0500 Received: (qmail 45515 invoked by uid 1000); 22 Jan 2021 11:20:19 -0500 Date: Fri, 22 Jan 2021 11:20:19 -0500 From: Alan Stern To: Pete Zaitcev Cc: Jeremy Figgins , gregkh@linuxfoundation.org, linux-usb@vger.kernel.org Subject: Re: [PATCH] USB: usblp: add USBLP_QUIRK_NO_SET_INTF flag Message-ID: <20210122162019.GA43566@rowland.harvard.edu> References: <20210117234416.49d59761@suzdal.zaitcev.lan> <20210118163117.GA142198@rowland.harvard.edu> <20210121131954.7103881d@suzdal.zaitcev.lan> <20210121192929.GA12502@rowland.harvard.edu> <20210121170249.4081af4c@suzdal.zaitcev.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210121170249.4081af4c@suzdal.zaitcev.lan> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org On Thu, Jan 21, 2021 at 05:02:49PM -0600, Pete Zaitcev wrote: > On Thu, 21 Jan 2021 14:29:29 -0500 > Alan Stern wrote: > > > > I'm also concerned about regressions. This is a legacy class driver, > > > only used where CUPS is not applicable, mostly with truly ancient > > > devices. So yes, setting a zero altsetting after enumeration should > > > be unnecessary. But you never know with the old firmware. > > > How about skipping the call whenever the interface has only one > > altsetting? > > Do you mean when it's only one and not equal to zero? If there's only one, it _has_ to be equal to 0. According to section 9.2.3 of the USB-2 spec: Alternate settings range from zero to one less than the number of alternate settings for a specific interface. > BTW, one other thing bothers me. Jeremy confirmed that my patch > worked, which skips the call when USB_QUIRK_NO_SET_INTF is set. > But if we look into drivers/usb/core/message.c, the control > exchange to set the altsetting is skipped in that case anyway. > So, usblp was calling usb_set_protocol, the suspect control was > skipped, but something else caused a problem. Could it be the > attempt to clear halt that triggered the problem? It could very well be. The printer might not reset the endpoint toggle when it gets the Clear-Halt request. It's also possible that when the quirk flag wasn't set (so the Set-Interface request was issued), the printer failed reset the endpoint toggle. Alan Stern