From patchwork Thu May 7 20:08:47 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Doug Anderson X-Patchwork-Id: 214009 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=-9.8 required=3.0 tests=DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED, USER_AGENT_GIT 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 101CAC54E49 for ; Thu, 7 May 2020 20:09:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DFE542173E for ; Thu, 7 May 2020 20:09:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="m5ylYMv8" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728632AbgEGUJO (ORCPT ); Thu, 7 May 2020 16:09:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45856 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1728625AbgEGUJN (ORCPT ); Thu, 7 May 2020 16:09:13 -0400 Received: from mail-pl1-x642.google.com (mail-pl1-x642.google.com [IPv6:2607:f8b0:4864:20::642]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DC36DC05BD0A for ; Thu, 7 May 2020 13:09:12 -0700 (PDT) Received: by mail-pl1-x642.google.com with SMTP id b8so2387453plm.11 for ; Thu, 07 May 2020 13:09:12 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=JZVfMDRlaZxQ6qpzAMsiTzN4YCAYznWKH75NGk0mLe0=; b=m5ylYMv87Zesz+z8ZAznR4kWc9TIjqXmxiLRRY8QyOpCZOwt00FTXHCWaihQzLwGTB /kjZ0p7FzdVuwoHXJtcPF3yVROz9sUTpYmZCbApuKUmPUpqHuEyGNlO3TyZwioK9zYWZ M773j7obrswcIlQPjJ858TSOKYbtG52zYMVnA= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=JZVfMDRlaZxQ6qpzAMsiTzN4YCAYznWKH75NGk0mLe0=; b=ZRBiCVQOoEOPehFyiU9932soZCNUQzp/9Cf/MAjvENdYPHQJEelTdE8N09K6GxnL+4 8ACESHCYBCU/nWm7FYlq0h2iA4t5XsUFsARUCINv4exZbxJPfcJo7pO+FGfi0wR+dNf+ 0mlrBPFB1guMvyxz4lG548lhTlNJvgT6+841se2V0HcZU4apeF8CSNwI3or//tCN7j0O x7icivw6pBgSGJlrx2wYR/WnJpBsCuL0y6XpojL28mP6jrrky6llZoyuKYyIR3yVzKQc HQr675lxlcAe0Xi2tU0ipaAV2LDk0BYwWzNpjVO7E4ksEY2OdkFqWgRmibVxOmRkw5XN fQPw== X-Gm-Message-State: AGi0PuY951uhphDma7NCTNvTPjIv64PDIyeYS92SJSJE0bvEGRKuyaT+ E8Awei9rirLRdKtX3n2XHq0UVw== X-Google-Smtp-Source: APiQypJWVjHYI0dqkVdBU1DEnnSramGm6bwNGEmhZQc/6xZdlZXzI9QuauPG2Tcya5C3/lJNRD27RQ== X-Received: by 2002:a17:902:c193:: with SMTP id d19mr15373854pld.60.1588882152281; Thu, 07 May 2020 13:09:12 -0700 (PDT) Received: from tictac2.mtv.corp.google.com ([2620:15c:202:1:24fa:e766:52c9:e3b2]) by smtp.gmail.com with ESMTPSA id d203sm5547601pfd.79.2020.05.07.13.09.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 07 May 2020 13:09:11 -0700 (PDT) From: Douglas Anderson To: jason.wessel@windriver.com, daniel.thompson@linaro.org, gregkh@linuxfoundation.org Cc: corbet@lwn.net, frowand.list@gmail.com, bjorn.andersson@linaro.org, linux-serial@vger.kernel.org, mingo@redhat.com, hpa@zytor.com, jslaby@suse.com, kgdb-bugreport@lists.sourceforge.net, sumit.garg@linaro.org, will@kernel.org, tglx@linutronix.de, agross@kernel.org, catalin.marinas@arm.com, bp@alien8.de, Douglas Anderson , Andrew Morton , Juergen Gross , Mauro Carvalho Chehab , Pawan Gupta , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v4 09/12] Documentation: kgdboc: Document new kgdboc_earlycon parameter Date: Thu, 7 May 2020 13:08:47 -0700 Message-Id: <20200507130644.v4.9.I7d5eb42c6180c831d47aef1af44d0b8be3fac559@changeid> X-Mailer: git-send-email 2.26.2.645.ge9eca65c58-goog In-Reply-To: <20200507200850.60646-1-dianders@chromium.org> References: <20200507200850.60646-1-dianders@chromium.org> MIME-Version: 1.0 Sender: linux-serial-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org The recent patch ("kgdboc: Add kgdboc_earlycon 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 "kgdboc_earlycon" 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 "kgdboc_earlycon" works in combination with "kgdboc" and is backed by boot consoles. Signed-off-by: Douglas Anderson Reviewed-by: Greg Kroah-Hartman Reviewed-by: Daniel Thompson --- Changes in v4: - s/The the/The/ Changes in v3: - Added example in kgdb.rst - Removed unneeded sentence in kerenel-parameters doc. - Renamed earlycon_kgdboc to kgdboc_earlycon. - Suggest people use kgdboc_earlycon instead of ekgdboc. Changes in v2: None .../admin-guide/kernel-parameters.txt | 20 ++++++++++++++++ Documentation/dev-tools/kgdb.rst | 24 +++++++++++++++++++ 2 files changed, 44 insertions(+) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 7bc83f3d9bdf..2cbde9ea476d 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -1190,6 +1190,11 @@ 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. For early debugging + via a serial port see kgdboc_earlycon instead. + edd= [EDD] Format: {"off" | "on" | "skip[mbr]"} @@ -2105,6 +2110,21 @@ kms, kbd format: kms,kbd kms, kbd and serial format: kms,kbd,[,baud] + kgdboc_earlycon= [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 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. It's OK to leave the value + blank and the first boot console that implements + read() will be picked. + kgdbwait [KGDB] Stop kernel execution and enter the kernel debugger at the earliest opportunity. diff --git a/Documentation/dev-tools/kgdb.rst b/Documentation/dev-tools/kgdb.rst index d38be58f872a..61293f40bc6e 100644 --- a/Documentation/dev-tools/kgdb.rst +++ b/Documentation/dev-tools/kgdb.rst @@ -274,6 +274,30 @@ 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: ``kgdboc_earlycon`` +------------------------------------- + +If you specify the kernel parameter ``kgdboc_earlycon`` 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 ``kgdboc_earlycon`` 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. Note that names that +are registered through the boot console layer and the tty layer are not +the same for the same port. + +For instance, on one board to be explicit you might do:: + + kgdboc_earlycon=qcom_geni kgdboc=ttyMSM0 + +If the only boot console on the device was "qcom_geni", you could simplify:: + + kgdboc_earlycon kgdboc=ttyMSM0 + Kernel parameter: ``kgdbwait`` ------------------------------