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=-6.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 688D3C54FD0 for ; Mon, 27 Apr 2020 16:46:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 42CB02080C for ; Mon, 27 Apr 2020 16:46:29 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="h89b6fSs" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726312AbgD0QqY (ORCPT ); Mon, 27 Apr 2020 12:46:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55656 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726282AbgD0QqY (ORCPT ); Mon, 27 Apr 2020 12:46:24 -0400 Received: from mail-wr1-x443.google.com (mail-wr1-x443.google.com [IPv6:2a00:1450:4864:20::443]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C7BF7C03C1A7 for ; Mon, 27 Apr 2020 09:46:23 -0700 (PDT) Received: by mail-wr1-x443.google.com with SMTP id s10so21390804wrr.0 for ; Mon, 27 Apr 2020 09:46:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=AFi2Ya3qM5IG+jnvqV1yuZyqNjUjwvEPZevqNfZVj0Y=; b=h89b6fSsTBUeL/XipyElSwPh022ivI7iy5S/qxb+B/YEFMXucgbgOPMaB5I8zHmo3G LRWpG0yPHRoPm6hWulcNTa8EZpmSU1ehlxrUGamES39kPwX8I0j/A+0KZg7hPbEs+0ks HANPmqjxSzMVM627SPxh1zTvoq9vHdnqsYVlJLIsHlzUsz3AmLrZdNJaY2bMEyz4RN+E NUpREb4sDwp8b2vh1zjq7PTy4S4t+pYLtsg99Q5g3VduUeMbXnv7Nu100uduQeC6sixW KMe2/BjTYwmqPbUi0wUvp7QccKp6gT4ao065bGV2099c9BJ1ORrE1ANzXHHED1u/7sCf qvnw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=AFi2Ya3qM5IG+jnvqV1yuZyqNjUjwvEPZevqNfZVj0Y=; b=j6CqHDlI8sZuChlIKxaliq138r3RFlPwsdJ/f2xEvGBIdkZw8yBrte+EeKDWFhoDrv /4h9ZsBh+BL8qO/xWOPgSlhBmnl6j4pQYDxkxMhn0KfP8s4MMeWo4igpWU5uixNMAClw o8JuYoZ0GdqGCBXJT62or46VsZU7QyuouUc0W7pXfrE/lLb8NeWDb9+3R8Farwl1htKS hL8pb/6q94Sbu6LwB4AwrLTHRf6NnMsyRuHIHwCtbRya/vssME8flgFtMJLNMFtrA2+6 WcVSvMbBwtlTVIxYjxTOOtwV6AvayViS7NfDq4vsqoG07t+OlkFKf6SVHBqSJcZX9HaI IMOg== X-Gm-Message-State: AGi0PuZ2T+ruevBOngsppMdATy5J9bVtBk4oDzgUYxmHS0HNusfs460Y TuZw8XIz4+z59lHAd5JQNR8EMg== X-Google-Smtp-Source: APiQypJ51FxUeaZo6yUU8t+LqTak9jj4U50akJER7m2MFUmNuUtXtokVlL35B4R3u3x89HQbdmY3Ng== X-Received: by 2002:adf:e944:: with SMTP id m4mr27910229wrn.366.1588005982418; Mon, 27 Apr 2020 09:46:22 -0700 (PDT) Received: from holly.lan (cpc141214-aztw34-2-0-cust773.18-1.cable.virginm.net. [86.9.19.6]) by smtp.gmail.com with ESMTPSA id x18sm21079430wrs.11.2020.04.27.09.46.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 27 Apr 2020 09:46:21 -0700 (PDT) Date: Mon, 27 Apr 2020 17:46:19 +0100 From: Daniel Thompson To: Douglas Anderson Cc: jason.wessel@windriver.com, gregkh@linuxfoundation.org, kgdb-bugreport@lists.sourceforge.net, mingo@redhat.com, hpa@zytor.com, bp@alien8.de, linux-serial@vger.kernel.org, agross@kernel.org, tglx@linutronix.de, frowand.list@gmail.com, bjorn.andersson@linaro.org, jslaby@suse.com, catalin.marinas@arm.com, corbet@lwn.net, will@kernel.org, Andrew Morton , Borislav Petkov , Juergen Gross , Mauro Carvalho Chehab , Pawan Gupta , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 7/9] Documentation: kgdboc: Document new earlycon_kgdboc parameter Message-ID: <20200427164619.kw4mihmoxmxzjk66@holly.lan> References: <20200421211447.193860-1-dianders@chromium.org> <20200421141234.v2.7.I7d5eb42c6180c831d47aef1af44d0b8be3fac559@changeid> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200421141234.v2.7.I7d5eb42c6180c831d47aef1af44d0b8be3fac559@changeid> Sender: linux-serial-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org On Tue, Apr 21, 2020 at 02:14:45PM -0700, Douglas Anderson wrote: > The recent patch ("kgdboc: Add earlycon_kgdboc to support early kgdb > using boot consoles") adds a new kernel command line parameter. > Document it. > > Note that the patch adding the feature does some comparing/contrasting > of "earlycon_kgdboc" vs. the existing "ekgdboc". See that patch for > more details, but briefly "ekgdboc" can be used _instead_ of "kgdboc" > and just makes "kgdboc" do its normal initialization early (only works > if your tty driver is already ready). The new "earlycon_kgdboc" works > in combination with "kgdboc" and is backed by boot consoles. > > Signed-off-by: Douglas Anderson > --- > > Changes in v2: None > > .../admin-guide/kernel-parameters.txt | 20 +++++++++++++++++++ > Documentation/dev-tools/kgdb.rst | 14 +++++++++++++ > 2 files changed, 34 insertions(+) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index f2a93c8679e8..588625ec2993 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -1132,6 +1132,22 @@ > address must be provided, and the serial port must > already be setup and configured. > > + earlycon_kgdboc= [KGDB,HW] > + If the boot console provides the ability to read > + characters and can work in polling mode, you can use > + this parameter to tell kgdb to use it as a backend > + until the normal console is registered. Intended to > + be used together with the kgdboc parameter which > + specifies the normal console to transition to. > + > + The the name of the early console should be specified > + as the value of this parameter. Note that the name of > + the early console might be different than the tty > + name passed to kgdboc. If only one boot console with > + a read() function is enabled it's OK to leave the > + value blank and the first boot console that implements > + read() will be picked. There's no need for the "If only one boot console with a read() funcuiton is enabled" here, Seeing this in alphabetic order in this patch it also crosses my mind that kgdboc_earlycon might be a better name so that is sorts closer to the other kgdb options. This is a kgdboc feature that uses earlycon not an earlycon feature that uses kgdboc. > + > earlyprintk= [X86,SH,ARM,M68k,S390] > earlyprintk=vga > earlyprintk=sclp > @@ -1190,6 +1206,10 @@ > This is designed to be used in conjunction with > the boot argument: earlyprintk=vga > > + This parameter works in place of the kgdboc parameter > + but can only be used if the backing tty is available > + very early in the boot process. > + I wonder if pragmatic advice is more useful: For early debugging via a serial port see earlycon_kgdboc instead. > edd= [EDD] > Format: {"off" | "on" | "skip[mbr]"} > > diff --git a/Documentation/dev-tools/kgdb.rst b/Documentation/dev-tools/kgdb.rst > index d38be58f872a..c0b321403d9a 100644 > --- a/Documentation/dev-tools/kgdb.rst > +++ b/Documentation/dev-tools/kgdb.rst > @@ -274,6 +274,20 @@ don't like this are to hack gdb to send the :kbd:`SysRq-G` for you as well as > on the initial connect, or to use a debugger proxy that allows an > unmodified gdb to do the debugging. > > +Kernel parameter: ``earlycon_kgdboc`` > +------------------------------------- > + > +If you specify the kernel parameter ``earlycon_kgdboc`` and your serial > +driver registers a boot console that supports polling (doesn't need > +interrupts and implements a nonblocking read() function) kgdb will attempt > +to work using the boot console until it can transition to the regular > +tty driver specified by the ``kgdboc`` parameter. > + > +Normally there is only one boot console (especially that implements the > +read() function) so just adding ``earlycon_kgdboc`` on its own is > +sufficient to make this work. If you have more than one boot console you > +can add the boot console's name to differentiate. > + I think we need an example here. The example in the patch header for the previous patch was useful (at least for me). Daniel.