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 D0B7FC433E0 for ; Fri, 22 Jan 2021 16:47:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 891A523AA1 for ; Fri, 22 Jan 2021 16:47:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729370AbhAVQXI (ORCPT ); Fri, 22 Jan 2021 11:23:08 -0500 Received: from netrider.rowland.org ([192.131.102.5]:50241 "HELO netrider.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1729367AbhAVQW4 (ORCPT ); Fri, 22 Jan 2021 11:22:56 -0500 Received: (qmail 45621 invoked by uid 1000); 22 Jan 2021 11:22:12 -0500 Date: Fri, 22 Jan 2021 11:22:12 -0500 From: Alan Stern To: Jeremy Figgins Cc: Pete Zaitcev , gregkh@linuxfoundation.org, linux-usb@vger.kernel.org Subject: Re: [PATCH] USB: usblp: add USBLP_QUIRK_NO_SET_INTF flag Message-ID: <20210122162212.GB43566@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> <2d9bf7fd-918c-c5cb-d2d3-7cd9a86b451e@jeremyfiggins.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2d9bf7fd-918c-c5cb-d2d3-7cd9a86b451e@jeremyfiggins.com> 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 07:06:27PM -0600, Jeremy Figgins wrote: > On 1/21/21 5:02 PM, 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? > > > > 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? > > > > -- Pete > > > > > In my debugging, I found that it was the calls to usb_control_msg_send() in > both usb_set_interface() and usb_clear_halt() caused the printer to lockup. > I suppose another way to resolve this would to have a flag to prevent > usb_clear_halt()'s call to usb_control_msg_send(), but I'm not an expert in > USB, so I'm not sure of the ramifications of that. The simplest solution in all cases is just to avoid calling either usb_set_interface or usb_clear_halt. Especially since in cases where the interface has only one altsetting, neither call should be necessary. Alan Stern