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=-1.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 592A7C282CE for ; Wed, 22 May 2019 18:10:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 30B2720863 for ; Wed, 22 May 2019 18:10:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="frr1iTSy" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729161AbfEVSKh (ORCPT ); Wed, 22 May 2019 14:10:37 -0400 Received: from mail-it1-f196.google.com ([209.85.166.196]:54669 "EHLO mail-it1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727975AbfEVSKg (ORCPT ); Wed, 22 May 2019 14:10:36 -0400 Received: by mail-it1-f196.google.com with SMTP id h20so5126752itk.4 for ; Wed, 22 May 2019 11:10:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=3TUaQnKxGVlpWSPefIyk2E07CFvwMDXGPaWjCwdOzPc=; b=frr1iTSygWFPnr5/ey27pxt1cfBtzPKcb5lZDA/fu8dE9SjUZ0g+PVcc06KiQ9/wJp HNO6AWj6TYApsqV+IK+BQsqd54H5A/bdFsoEMMgsXbs0nAv2poHnHbB45XVWALyR5Br5 ymgG+BfyWDKpG/NnKJ6OQjG2wMuS9A+Ofk4AE2P05OaUy1D2AgH5cr+HLItgD0A6epA2 zqkE3JWfzJvbob/DvPkPYG/u4MinzMxlP/cUqevtnoaIDimZ7e3vtLPo8dyZ/vmO0itS jOLex57FcbLpUAhIXMukWVDiCsoPvAIAbP7eXp3BA6oUgC3ESC5KHfIMt2+21yv+A8mQ Fafw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=3TUaQnKxGVlpWSPefIyk2E07CFvwMDXGPaWjCwdOzPc=; b=O7++32y1DsOHuImmxD+xQT/CXQ6FMQyWz6Eg9fLk5syYBf+E8hOJQwfVfHulbfLOG6 VbistFikCDUTD2ZVVpruhlfkBnKnyzxCliUh3kMkd18a6cyOMjqXvjR/I1yx9Ih3CeOM qMLtGxLiZGQ8xut4ZRmkUFCTBxk2Sxy36IDBCXx5BHKEHS4VcqPZytA8UbQEOhk2c7cm S5L1lB+iFU5NY6Yp3k7VbPcIbciYshM/LlvxNAyOmVETBkLn3QNofwI/AIRau3gKiq6D qv8APDf97DwTVua1NeC3SGHQ9pXSV8088VhIhd2NELcirkx0yh7lmBsCjkbVXgpFD5nL h4dw== X-Gm-Message-State: APjAAAWLq5rULYH5CdFpJl6g/R5bA1dC0qUQdj3vtU/MaRWg0Ui5qSBi 3xnc0xbyQwSQkOSR4w5zSmwzZ9AYPh6fw2P38dtPlsTK X-Google-Smtp-Source: APXvYqz9eLUgCjZxLo/vpG3af0L6etYrvYVd0GrTMp4ahq2xE4ZtnQGK9joeaxrO0qQ5Lx7oxC4w9UNyJNOsWgfJk0w= X-Received: by 2002:a02:ad09:: with SMTP id s9mr20093787jan.17.1558548636248; Wed, 22 May 2019 11:10:36 -0700 (PDT) MIME-Version: 1.0 References: <20190522071227.31488-1-andrew.smirnov@gmail.com> <20190522071227.31488-3-andrew.smirnov@gmail.com> <1558517601.2624.32.camel@pengutronix.de> In-Reply-To: From: Chris Healy Date: Wed, 22 May 2019 11:10:25 -0700 Message-ID: Subject: Re: [PATCH 3/3] ARM: dts: imx6: rdu2: Limit USBH1 to Full Speed To: Andrey Smirnov Cc: Lucas Stach , linux-arm-kernel , Shawn Guo , Fabio Estevam , linux-kernel Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > > Am Mittwoch, den 22.05.2019, 00:12 -0700 schrieb Andrey Smirnov: > > > Cabling used to connect devices to USBH1 on RDU2 does not meet USB > > > spec cable quality and cable length requirements to operate at High > > > Speed, so limit the port to Full Speed only. > > > > Really? I thought this issue is specific to the RDU1, but you've been > > looking at this USB stuff for a lot longer than me. > > > > I am merely a messenger here. I didn't personally verify this to be > the case, so your knowledge is probably as good as mine. Chris > reported this based on feedback from their EE team, so he should know > all of the details better. The issue is less about the internals of the device and more about the cabling that the device is connected to. In the target application of this device, the USB cables are almost always longer than the spec limit of the USB standard for high speed. Given our use cases, we don't have need for high speed so limiting the max speed to full speed is the way we work around cables that are too long for stable high speed operation. We have validated that running with full speed does mitigate the problems experienced when attempting to run with high speed on the target application installations. Reviewed-by: Chris Healy