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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 9313AC433DF for ; Thu, 14 May 2020 16:26:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7BE4E20675 for ; Thu, 14 May 2020 16:26:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726123AbgENQ0F (ORCPT ); Thu, 14 May 2020 12:26:05 -0400 Received: from netrider.rowland.org ([192.131.102.5]:45369 "HELO netrider.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1726117AbgENQ0F (ORCPT ); Thu, 14 May 2020 12:26:05 -0400 Received: (qmail 10249 invoked by uid 500); 14 May 2020 12:26:04 -0400 Date: Thu, 14 May 2020 12:26:04 -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: <20200514162604.GA9571@rowland.harvard.edu> References: <20200513213620.21541-1-b-liu@ti.com> <20200514013205.GA10515@rowland.harvard.edu> <20200514142803.GA11463@iaqt7> <20200514144053.GC12181@rowland.harvard.edu> <20200514150259.GB11463@iaqt7> <20200514153731.GC11463@iaqt7> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200514153731.GC11463@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 10:37:31AM -0500, Bin Liu wrote: > On Thu, May 14, 2020 at 10:02:59AM -0500, Bin Liu wrote: > > On Thu, May 14, 2020 at 10:40:53AM -0400, Alan Stern wrote: > > > 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). > > > > Yes, I know this. But we don't have a solution then. I cannot add > > resubmit delay in those ~500 device drivers. > > By the way I don't think noise could last long enough to cause 3-strikes > error. A shortest USB packet is about 3-bytes long, a noise should be > just a glitch, it won't last at least 3-bytes long to supress the bus > and 3 times on the exact timing when the host expecting a response > packet. I cannot think of any other reason which can cause the 3-strikes > error other than the device is off the bus. Heh. I heard from somebody (many years ago) about a setup where one of his USB devices stopped working whenever he turned on the fluorescent lights. Yes, I agree that noise is pretty uncommon, and the vast majority of 3-strikes errors are caused by disconnection or device firmware bugs. That's why I didn't NAK this patch. Still, it's worth pointing out that this change abuses the API (perhaps mentioning it in a comment). And it still would be preferable to fix the drivers in question, impractical though that may be. (I have a hard time believing there are really 500 of them getting this wrong...) Alan Stern