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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 23DA3C433E0 for ; Wed, 20 May 2020 16:38:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 040DB2065F for ; Wed, 20 May 2020 16:38:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726806AbgETQil (ORCPT ); Wed, 20 May 2020 12:38:41 -0400 Received: from netrider.rowland.org ([192.131.102.5]:51121 "HELO netrider.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1726439AbgETQil (ORCPT ); Wed, 20 May 2020 12:38:41 -0400 Received: (qmail 12889 invoked by uid 1000); 20 May 2020 12:38:40 -0400 Date: Wed, 20 May 2020 12:38:40 -0400 From: Alan Stern To: Rik van Riel Cc: linux-usb , alsa-devel@alsa-project.org, "linux-kernel@vger.kernel.org" , Mathias Nyman , Greg Kroah-Hartman , Jaroslav Kysela , Takashi Iwai Subject: Re: XHCI vs PCM2903B/PCM2904 part 2 Message-ID: <20200520163840.GA11084@rowland.harvard.edu> References: <273cc1c074cc4a4058f31afe487fb233f5cf0351.camel@surriel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <273cc1c074cc4a4058f31afe487fb233f5cf0351.camel@surriel.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-usb-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org On Wed, May 20, 2020 at 07:26:57AM -0400, Rik van Riel wrote: > After a few more weeks of digging, I have come to the tentative > conclusion that either the XHCI driver, or the USB sound driver, > or both, fail to handle USB errors correctly. > > I have some questions at the bottom, after a (brief-ish) explanation > of exactly what seems to go wrong. > > TL;DR: arecord from a misbehaving device can hang forever > after a USB error, due to poll on /dev/snd/timer never returning. > > The details: under some mysterious circumstances, the PCM290x > family sound chips can send more data than expected during an > isochronous transfer, leading to a babble error. Those Do these chips connect as USB-3 devices or as USB-2? (I wouldn't expect an audio device to use USB-3; it shouldn't need the higher bandwidth.) > circumstances seem to in part depend on the USB host controller > and/or the electrical environment, since the chips work just > fine for most people. > > Receiving data past the end of the isochronous transfer window > scheduled for a device results in the XHCI controller throwing > a babble error, which moves the endpoint into halted state. > > This is followed by the host controller software sending a > reset endpoint command, and moving the endpoint into stopped > state, as specified on pages 164-165 of the XHCI specification. In general, errors such as babble are not supposed to stop isochronous endpoints. > However, the USB sound driver seems to have no idea that this > error happened. The function retire_capture_urb looks at the > status of each isochronous frame, but seems to be under the > assumption that the sound device just keeps on running. This is appropriate, for the reason mentioned above. > The function snd_complete_urb seems to only detect that the > device is not running if usb_submit_urb returns a failure. > > err = usb_submit_urb(urb, GFP_ATOMIC); > if (err == 0) > return; > > usb_audio_err(ep->chip, "cannot submit urb (err = %d)\n", err); > > if (ep->data_subs && ep->data_subs->pcm_substream) { > substream = ep->data_subs->pcm_substream; > snd_pcm_stop_xrun(substream); > } > > However, the XHCI driver will happily submit an URB to a > stopped device. Do you mean "stopped device" or "stopped endpoint"? > Looking at the call trace usb_submit_urb -> > xhci_urb_enqueue -> xhci_queue_isoc_tx_prepare -> prepare_ring, > you can see this code: > > /* Make sure the endpoint has been added to xHC schedule */ > switch (ep_state) { > ... > case EP_STATE_HALTED: > xhci_dbg(xhci, "WARN halted endpoint, queueing URB anyway.\n"); > case EP_STATE_STOPPED: > case EP_STATE_RUNNING: > break; > > This leads me to a few questions: > - should retire_capture_urb call snd_pcm_stop_xrun, > or another function like it, if it sees certain > errors in the iso frame in the URB? No. Isochronous endpoints are expected to encounter errors from time to time; that is the nature of isochronous communications. You're supposed to ignore the errors (skip over any bad data) and keep going. > - should snd_complete_urb do something with these > errors, too, in case they happen on the sync frames > and not the data frames? > - does the XHCI code need to ring the doorbell when > submitting an URB to a stopped device, or is it > always up to the higher-level driver to fully reset > the device before it can do anything useful? In this case it is not up to the higher-level driver. > - if a device in stopped state does not do anything > useful, should usb_submit_urb return an error? The notion of "stopped state" is not part of USB-2. As a result, it should be handled entirely within the xhci-hcd driver. (A non-isochronous endpoint can be in the "halted" state. But obviously this isn't what you're talking about.) > - how should the USB sound driver recover from these > occasional and/or one-off errors? stop the sound > stream, or try to reinitialize the device and start > recording again? As far as I know, it should do its best to continue (perhaps fill in missing data with zeros). Alan Stern > I am willing to write patches and can test with my > setup, but both the sound code and the USB code are > new to me so I would like to know what direction I > should go in :)