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=-3.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 6A903C433E0 for ; Thu, 14 May 2020 14:40:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 40F5A205CB for ; Thu, 14 May 2020 14:40:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726073AbgENOky (ORCPT ); Thu, 14 May 2020 10:40:54 -0400 Received: from netrider.rowland.org ([192.131.102.5]:53821 "HELO netrider.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1726066AbgENOky (ORCPT ); Thu, 14 May 2020 10:40:54 -0400 Received: (qmail 30396 invoked by uid 500); 14 May 2020 10:40:53 -0400 Date: Thu, 14 May 2020 10:40:53 -0400 From: Alan Stern To: Bin Liu , linux-usb@vger.kernel.org Subject: Re: [PATCH] usb: musb: return -ESHUTDOWN in urb when three-strikes error happened Message-ID: <20200514144053.GC12181@rowland.harvard.edu> References: <20200513213620.21541-1-b-liu@ti.com> <20200514013205.GA10515@rowland.harvard.edu> <20200514142803.GA11463@iaqt7> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200514142803.GA11463@iaqt7> Sender: linux-usb-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org On Thu, May 14, 2020 at 09:28:03AM -0500, Bin Liu wrote: > On Wed, May 13, 2020 at 09:32:05PM -0400, Alan Stern wrote: > > On Wed, May 13, 2020 at 04:36:20PM -0500, Bin Liu wrote: > > > When a USB device attached to a hub got disconnected, MUSB controller > > > generates RXCSR_RX_ERROR interrupt for the 3-strikes-out error. > > > > > > Currently the MUSB host driver returns -EPROTO in current URB, then the > > > USB device driver could immediately resubmit the URB which causes MUSB > > > generate RXCSR_RX_ERROR interrupt again. This circle causes interrupt > > > storm then the hub never got a chance to report the USB device detach. > > > > > > To fix the interrupt storm, change the URB return code to -ESHUTDOWN for > > > MUSB_RXCSR_H_ERROR interrupt, so that the USB device driver will not > > > immediately resubmit the URB. > > > > > > Signed-off-by: Bin Liu > > > > Strictly speaking, this is not the right thing to do. It goes against > > the API described in error-codes.rst. A better approach would be to fix > > error-codes.rst says: > > -ESHUTDOWN The device or host controller has been > disabled due to some problem that could not > be worked around, such as a physical > disconnect. > > So -ESHUTDOWN is applicable in this case - the device is disconnected > behind a hub. Yes, but you don't _know_ that the device was disconnected. All you know is that there was a 3-strikes error. Other problems can cause such errors (noise, for example). Alan Stern