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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,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 720ECC43460 for ; Tue, 27 Apr 2021 13:06:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 379D36115C for ; Tue, 27 Apr 2021 13:06:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236008AbhD0NHO (ORCPT ); Tue, 27 Apr 2021 09:07:14 -0400 Received: from mga09.intel.com ([134.134.136.24]:16490 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235795AbhD0NHO (ORCPT ); Tue, 27 Apr 2021 09:07:14 -0400 IronPort-SDR: VUHxa8mAROe/IsTc5dnCt84zfX3CiTFG7REsnml2CAfMgiacruIICsTNeelaqxVxnyvkcBH95j pVe6fedBL+vw== X-IronPort-AV: E=McAfee;i="6200,9189,9966"; a="196615230" X-IronPort-AV: E=Sophos;i="5.82,254,1613462400"; d="scan'208";a="196615230" Received: from fmsmga005.fm.intel.com ([10.253.24.32]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 27 Apr 2021 06:06:24 -0700 IronPort-SDR: K7Np3LQlVoiWluaCTJ2FhoyRO9jf9C1CNb5JOOaVp44Xg9W3y+DRBiB/QbRchsDnrwzusNwyA8 Bh1mQgIX/amQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.82,254,1613462400"; d="scan'208";a="618919372" Received: from mattu-haswell.fi.intel.com (HELO [10.237.72.170]) ([10.237.72.170]) by fmsmga005.fm.intel.com with ESMTP; 27 Apr 2021 06:06:22 -0700 Subject: Re: [PATCH v2 3/7] usb: xhci: Check for blocked disconnection To: Thinh Nguyen , Felipe Balbi , Greg Kroah-Hartman , linux-usb@vger.kernel.org, Mathias Nyman Cc: John Youn References: <07196754c6de290bb46cc235ce6e96c5df304150.1618014279.git.Thinh.Nguyen@synopsys.com> From: Mathias Nyman Autocrypt: addr=mathias.nyman@linux.intel.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <07196754c6de290bb46cc235ce6e96c5df304150.1618014279.git.Thinh.Nguyen@synopsys.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org Hi Thinh Sorry about the delay. On 10.4.2021 3.47, Thinh Nguyen wrote: > If there is a device with active enhanced super-speed (eSS) isoc IN > endpoint(s) behind one or more eSS hubs, DWC_usb31 (v1.90a and prior) > host controller will not detect the device disconnection until no more > isoc URB is submitted. If there's a device disconnection, internally > the wait for tHostTransactionTimeout (USB 3.2 spec 8.13) blocks the > other endpoints from being scheduled. So, it blocks the interrupt > endpoint of the eSS hub indicating the port change status. > > This can be an issue for applications that continuously submitting isoc > URBs to the xHCI. To work around this, stop processing new URBs after 3 > consecutive isoc transaction errors. If new isoc transfers are queued > after the device is disconnected, the host will respond with USB > transaction error. After 3 consecutive USB transaction errors, the > driver can wait a period of time (at least 2 * largest periodic interval > of the topology) without ringing isoc endpoint doorbell to detect the > port change status. If there is no disconnection detected, ring the > endpoint doorbell to resume isoc transfers. Is that enough? many Isoc URBs queue 16 - 32 Isoc TRBs per URB. And drivers like UVC queue several URBs in advance. If I remember correctly then a transaction errors won't stop Isoch endpoints, so waiting for 2 * Interval after 3 consecutive transaction errors might not be enough. How about stopping the endpoint after 3 consecutive transaction errors, and restating it a bit later? > > This workaround tracks the max eSS periodic interval every time there's > an endpoint added or dropped, which happens when there's bandwidth > check. So, scan the topology and update the xhci->max_ess_interval > whenever there's a bandwidth check. Introduced a new flag > VDEV_DISCONN_CHECK_PENDING to prevent ringing the doorbell while waiting > for a disconnection status. After 2 * max_ess_interval time and no > disconnection detected, a delayed work will ring the doorbell to resume > the active isoc transfers. Sounds very elaborate for a vendor specific disconnect workaround. Isn't there a simpler way? Maybe stop all isoc in endpoints if one them has 3 consecutive transaction error, wait for 2x hub interrupt interval time, and then restart the endpoints if there is no disconnect? There is bigger concern with this series, it scatters a lot of vendor specific code around the generic xhci driver. It's not very clear afterwards what code is part of the workaround and what is generic code. We just got a lot of the Mediatek code moved to xhci-mtk*, maybe its time to add xhci-snps.c instead of using the generic platform driver with tons of workarounds and quirks. Thanks -Mathias