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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 D8F3DC433E0 for ; Wed, 20 May 2020 11:27:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B6E0B207C4 for ; Wed, 20 May 2020 11:27:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726846AbgETL1I (ORCPT ); Wed, 20 May 2020 07:27:08 -0400 Received: from shelob.surriel.com ([96.67.55.147]:52946 "EHLO shelob.surriel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726435AbgETL1I (ORCPT ); Wed, 20 May 2020 07:27:08 -0400 Received: from imladris.surriel.com ([96.67.55.152]) by shelob.surriel.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1jbMsE-0003xQ-7J; Wed, 20 May 2020 07:26:58 -0400 Message-ID: <273cc1c074cc4a4058f31afe487fb233f5cf0351.camel@surriel.com> Subject: XHCI vs PCM2903B/PCM2904 part 2 From: Rik van Riel To: linux-usb Cc: alsa-devel@alsa-project.org, "linux-kernel@vger.kernel.org" , Mathias Nyman , Greg Kroah-Hartman , Jaroslav Kysela , Takashi Iwai Date: Wed, 20 May 2020 07:26:57 -0400 Content-Type: multipart/signed; micalg="pgp-sha256"; protocol="application/pgp-signature"; boundary="=-KZ0PlQuw8u0ClyxHg+lW" User-Agent: Evolution 3.34.4 (3.34.4-1.fc31) MIME-Version: 1.0 Sender: linux-usb-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org --=-KZ0PlQuw8u0ClyxHg+lW Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable 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 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. 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. The function snd_complete_urb seems to only detect that the device is not running if usb_submit_urb returns a failure. err =3D usb_submit_urb(urb, GFP_ATOMIC); if (err =3D=3D 0) return; usb_audio_err(ep->chip, "cannot submit urb (err =3D %d)\n", err); if (ep->data_subs && ep->data_subs->pcm_substream) { substream =3D ep->data_subs->pcm_substream; snd_pcm_stop_xrun(substream); } However, the XHCI driver will happily submit an URB to a stopped device. 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? - 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? - if a device in stopped state does not do anything useful, should usb_submit_urb return an error? - 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? 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 :) --=20 All Rights Reversed. --=-KZ0PlQuw8u0ClyxHg+lW Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- iQEzBAABCAAdFiEEKR73pCCtJ5Xj3yADznnekoTE3oMFAl7FFAEACgkQznnekoTE 3oM+AAf+JhbuACD7UFirucp8tydQbMb1EuABebzvTo+DuA0miaAAYbfZu8o1g3P1 gg7edPquFrT88411j4qWGfHSBvG9n3WhF8qLm1aIdLB83K9Vi0R1oxDgizg8I4IR R/EO16XdMWsOKAsv4yiKtuDGUZ8Y+TuGivRts6bTKjwqxABOVeX82zCPmHOPe6dI z2EXhqmduk4W2Hfswz5ouBMHyNpPeMEMPWxlIwhU+d6a/5ZkhDcoWvaxC8sr5LRC W4LhSZINZsMt+tzjy1dv7EkTQz/gGBKU+ZnTrA5XZxLAT83Y2YmdQd+76UUmSyzl c9N17a9S0hnZ6luq73BDEh7vsj/ZZA== =8U/0 -----END PGP SIGNATURE----- --=-KZ0PlQuw8u0ClyxHg+lW--