From patchwork Mon Nov 20 22:33:35 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Simon Glass X-Patchwork-Id: 839806 X-Patchwork-Delegate: trini@ti.com Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=none (mailfrom) smtp.mailfrom=lists.denx.de (client-ip=81.169.180.215; helo=lists.denx.de; envelope-from=u-boot-bounces@lists.denx.de; receiver=) Authentication-Results: ozlabs.org; dkim=fail reason="signature verification failed" (2048-bit key; unprotected) header.d=google.com header.i=@google.com header.b="m8PT6yAi"; dkim-atps=neutral Received: from lists.denx.de (dione.denx.de [81.169.180.215]) by ozlabs.org (Postfix) with ESMTP id 3ygkFJ3YqZz9t20 for ; Tue, 21 Nov 2017 09:40:20 +1100 (AEDT) Received: by lists.denx.de (Postfix, from userid 105) id 36435C220F3; Mon, 20 Nov 2017 22:39:02 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on lists.denx.de X-Spam-Level: X-Spam-Status: No, score=-0.0 required=5.0 tests=RCVD_IN_DNSWL_BLOCKED, RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL, T_DKIM_INVALID autolearn=unavailable autolearn_force=no version=3.4.0 Received: from lists.denx.de (localhost [IPv6:::1]) by lists.denx.de (Postfix) with ESMTP id 7F25DC22105; Mon, 20 Nov 2017 22:36:07 +0000 (UTC) Received: by lists.denx.de (Postfix, from userid 105) id 323A8C22102; Mon, 20 Nov 2017 22:34:08 +0000 (UTC) Received: from mail-it0-f53.google.com (mail-it0-f53.google.com [209.85.214.53]) by lists.denx.de (Postfix) with ESMTPS id 032EFC220F3 for ; Mon, 20 Nov 2017 22:34:04 +0000 (UTC) Received: by mail-it0-f53.google.com with SMTP id x13so3760906iti.4 for ; Mon, 20 Nov 2017 14:34:03 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=sender:from:to:cc:subject:date:message-id:in-reply-to:references; bh=4WR+OO8gFCx2q9FZz1NXarF22Snqd2qBg2EVGr5TZC8=; b=m8PT6yAiBKfZrFtZp7NACP1/1B099gboszs1Js/KVfgUYrdpu9LWlUReVQnrb8tqDt Hd+tvDgIF0icmgpcFmdmp7zL0hT5g/PRmdBYVabGW8svYFacaq8BT0etblNfUp/iW7pY SpdCl/4ASiA4zZ0oi/qXHiowYRuImr+Y51wFWPBAh4izIg/iAcxrlcNDWycVR6pUBNav gj4Qx15dxX4XB127oq5Au5aISb8JDdATO3R136lR68E2WBbIrTz2GFjAJQYQNuOdb6S9 z/OBX2iBfA/zbUoPO7TknAv5f9m/lYEErmQR6TA6ipNXm4jR3tR1sLm2fLFZkdcTzIMR xsYA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:from:to:cc:subject:date:message-id :in-reply-to:references; bh=4WR+OO8gFCx2q9FZz1NXarF22Snqd2qBg2EVGr5TZC8=; b=BQ0LDmkWvcZ2hbv8uLPvcqb6eFT9cyYIFzO+MyHRoQ6txv3h9D0LzEMvEYlISzwdEl 71eqjiYtUVSIsCkmCvNKWwRqkbP4Ad+g8dmiY45+TZs94vk6BUSKmaqvhBhAKP199Esc 4YA9zj/7nHBBm45cGhudLpQnEh511QjHnVmLEJ0LBGt+YsOT5vf9tu63w9svQWYqUKJa I+8qw/NyGX5rpw+XpJ72NfOglZK0VMBJnJv14cmaw2YkCPJrGyBNqIYMeABeowqS9m7F g32tnl1GRyzx5FulGmIXqvVT9KtaGUvcd7Au7X+XxuKPZ6ltZ3x8wQCDKcBQMj15d+k2 lrhQ== X-Gm-Message-State: AJaThX4da7XTf4wrIbCToMA5sVgrA+u3o2i1hT1cTlnPLOyCgBjI/1EX /1YnJNjE3THmsaN4hRoLgXlo5w== X-Google-Smtp-Source: AGs4zMaOw8BEye06aQG3wmRMewCROzFPXAYKyNXe2H5hnX/2UmuJexPhEumzFNW+qtndYE3A3wfnSg== X-Received: by 10.36.95.5 with SMTP id r5mr6955226itb.70.1511217242383; Mon, 20 Nov 2017 14:34:02 -0800 (PST) Received: from kiwi.bld.corp.google.com ([100.101.164.89]) by smtp.gmail.com with ESMTPSA id 14sm4889944ior.48.2017.11.20.14.34.00 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 20 Nov 2017 14:34:01 -0800 (PST) Received: by kiwi.bld.corp.google.com (Postfix, from userid 121222) id 8CD9614001C; Mon, 20 Nov 2017 15:33:59 -0700 (MST) From: Simon Glass To: U-Boot Mailing List Date: Mon, 20 Nov 2017 15:33:35 -0700 Message-Id: <20171120223335.45852-15-sjg@chromium.org> X-Mailer: git-send-email 2.15.0.448.gf294e3d99a-goog In-Reply-To: <20171120223335.45852-1-sjg@chromium.org> References: <20171120223335.45852-1-sjg@chromium.org> Cc: Tom Rini Subject: [U-Boot] [PATCH v3 14/14] log: Add documentation X-BeenThere: u-boot@lists.denx.de X-Mailman-Version: 2.1.18 Precedence: list List-Id: U-Boot discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Errors-To: u-boot-bounces@lists.denx.de Sender: "U-Boot" Add documentation for the log system. Signed-off-by: Simon Glass Reviewed-by: Bin Meng Reviewed-by: Lukasz Majewski --- Changes in v3: - Rebase to master Changes in v2: - Drop the special log() functions from the README doc/README.log | 214 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 214 insertions(+) create mode 100644 doc/README.log diff --git a/doc/README.log b/doc/README.log new file mode 100644 index 00000000000..f653fe7d797 --- /dev/null +++ b/doc/README.log @@ -0,0 +1,214 @@ +Logging in U-Boot +================= + +Introduction +------------ + +U-Boot's internal operation involves many different steps and actions. From +setting up the board to displaying a start-up screen to loading an Operating +System, there are many component parts each with many actions. + +Most of the time this internal detail is not useful. Displaying it on the +console would delay booting (U-Boot's primary purpose) and confuse users. + +But for digging into what is happening in a particular area, or for debugging +a problem it is often useful to see what U-Boot is doing in more detail than +is visible from the basic console output. + +U-Boot's logging feature aims to satisfy this goal for both users and +developers. + + +Logging levels +-------------- + +There are a number logging levels available, in increasing order of verbosity: + + LOGL_EMERG - Printed before U-Boot halts + LOGL_ALERT - Indicates action must be taken immediate or U-Boot will crash + LOGL_CRIT - Indicates a critical error that will cause boot failure + LOGL_ERR - Indicates an error that may cause boot failure + LOGL_WARNING - Warning about an unexpected condition + LOGL_NOTE - Important information about progress + LOGL_INFO - Information about normal boot progress + LOGL_DEBUG - Debug information (useful for debugging a driver or subsystem) + LOGL_DEBUG_CONTENT - Debug message showing full message content + LOGL_DEBUG_IO - Debug message showing hardware I/O access + + +Logging category +---------------- + +Logging can come from a wide variety of places within U-Boot. Each log message +has a category which is intended to allow messages to be filtered according to +their source. + +The following main categories are defined: + + LOGC_NONE - Unknown category (e.g. a debug() statement) + UCLASS_... - Related to a particular uclass (e.g. UCLASS_USB) + LOGC_ARCH - Related to architecture-specific code + LOGC_BOARD - Related to board-specific code + LOGC_CORE - Related to core driver-model support + LOGC_DT - Related to device tree control + + +Enabling logging +---------------- + +The following options are used to enable logging at compile time: + + CONFIG_LOG - Enables the logging system + CONFIG_MAX_LOG_LEVEL - Max log level to build (anything higher is compiled + out) + CONFIG_LOG_CONSOLE - Enable writing log records to the console + +If CONFIG_LOG is not set, then no logging will be available. + +The above have SPL versions also, e.g. CONFIG_SPL_MAX_LOG_LEVEL. + + +Using DEBUG +----------- + +U-Boot has traditionally used a #define called DEBUG to enable debugging on a +file-by-file basis. The debug() macro compiles to a printf() statement if +DEBUG is enabled, and an empty statement if not. + +With logging enabled, debug() statements are interpreted as logging output +with a level of LOGL_DEBUG and a category of LOGC_NONE. + +The logging facilities are intended to replace DEBUG, but if DEBUG is defined +at the top of a file, then it takes precedence. This means that debug() +statements will result in output to the console and this output will not be +logged. + + +Logging destinations +-------------------- + +If logging information goes nowhere then it serves no purpose. U-Boot provides +several possible determinations for logging information, all of which can be +enabled or disabled independently: + + console - goes to stdout + + +Filters +------- + +Filters are attached to log drivers to control what those drivers emit. Only +records that pass through the filter make it to the driver. + +Filters can be based on several criteria: + + - maximum log level + - in a set of categories + - in a set of files + +If no filters are attached to a driver then a default filter is used, which +limits output to records with a level less than CONFIG_LOG_MAX_LEVEL. + + +Logging statements +------------------ + +The main logging function is: + + log(category, level, format_string, ...) + +Also debug() and error() will generate log records - these use LOG_CATEGORY +as the category, so you should #define this right at the top of the source +file to ensure the category is correct. + + +Code size +--------- + +Code size impact depends largely on what is enabled. The following numbers are +for snow, which is a Thumb-2 board: + +This series: adds bss +20.0 data +4.0 rodata +4.0 text +44.0 +CONFIG_LOG: bss -52.0 data +92.0 rodata -635.0 text +1048.0 +CONFIG_LOG_MAX_LEVEL=7: bss +188.0 data +4.0 rodata +49183.0 text +98124.0 + +The last option turns every debug() statement into a logging call, which +bloats the code hugely. The advantage is that it is then possible to enable +all logging within U-Boot. + + +To Do +----- + +There are lots of useful additions that could be made. None of the below is +implemented! If you do one, please add a test in test/py/tests/test_log.py + +Convenience functions to support setting the category: + + log_arch(level, format_string, ...) - category LOGC_ARCH + log_board(level, format_string, ...) - category LOGC_BOARD + log_core(level, format_string, ...) - category LOGC_CORE + log_dt(level, format_string, ...) - category LOGC_DT + +Convenience functions to support a category defined for a single file, for +example: + + #define LOG_CATEGORY UCLASS_USB + +all of these can use LOG_CATEGORY as the category, and a log level +corresponding to the function name: + + logc(level, format_string, ...) + +More logging destinations: + + device - goes to a device (e.g. serial) + buffer - recorded in a memory buffer + +Convert debug() statements in the code to log() statements + +Support making printf() emit log statements a L_INFO level + +Convert error() statements in the code to log() statements + +Figure out what to do with BUG(), BUG_ON() and warn_non_spl() + +Figure out what to do with assert() + +Add a way to browse log records + +Add a way to record log records for browsing using an external tool + +Add commands to add and remove filters + +Add commands to add and remove log devices + +Allow sharing of printf format strings in log records to reduce storage size +for large numbers of log records + +Add a command-line option to sandbox to set the default logging level + +Convert core driver model code to use logging + +Convert uclasses to use logging with the correct category + +Consider making log() calls emit an automatic newline, perhaps with a logn() + function to avoid that + +Passing log records through to linux (e.g. via device tree /chosen) + +Provide a command to access the number of log records generated, and the +number dropped due to them being generated before the log system was ready. + +Add a printf() format string pragma so that log statements are checked properly + +Enhance the log console driver to show level / category / file / line +information + +Add a command to add new log records and delete existing records. + +Provide additional log() functions - e.g. logc() to specify the category + +-- +Simon Glass +15-Sep-17