linux-kernel - [PATCH] char drivers: ramoops documentation

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Message-Id: <1312234010-18004-1-git-send-email-sergiu@chromium.org>
Date:	Mon,  1 Aug 2011 14:26:50 -0700
From:	Sergiu Iordache <sergiu@...omium.org>
To:	linux-doc@...r.kernel.org
Cc:	Randy Dunlap <rdunlap@...otime.net>, linux-kernel@...r.kernel.org,
	marco.stornelli@...il.com, Sergiu Iordache <sergiu@...omium.org>
Subject: [PATCH] char drivers: ramoops documentation

Add a documentation file describing the usage of Ramoops

Change-Id: I9dab9c4b9e4921b220574470372e330d32f9c63b
Signed-off-by: Sergiu Iordache <sergiu@...omium.org>
---
 Documentation/ramoops.txt |   67 +++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 67 insertions(+), 0 deletions(-)
 create mode 100644 Documentation/ramoops.txt

diff --git a/Documentation/ramoops.txt b/Documentation/ramoops.txt
new file mode 100644
index 0000000..ef606de
--- /dev/null
+++ b/Documentation/ramoops.txt
@@ -0,0 +1,67 @@
+Ramoops oops/panic logger
+=========================
+
+Sergiu Iordache <sergiu@...omium.org>
+
+Updated: 1 August 2011
+
+0. Introduction
+
+Ramoops is an oops/panic logger in RAM. It works by logging oopses and panics
+in a circular buffer. In order to work it needs a system with persistent RAM
+so that the content of that area can survive after a restart.
+
+1. Ramoops concepts
+
+Ramoops uses a predefined memory area to store the dump. The start and size of
+the memory area are set using two variables: "mem_address" for the start and
+"mem_size" for the size. Memory size will be rounded to a multiple of two.
+This memory area is divided into "record_size" chunks (also rounded to
+multiple of two) and each oops/panic writes a "record_size" chunk of
+information. Dumping both oopses and panics can be done by setting 1 in the
+"dump_oops" variable while setting 0 in that variable dumps only the panics.
+
+2. Setting the parameters
+
+Setting the ramoops parameters can be done in 2 different manners:
+ 1. Use the module parameters (which have the names of the variables described
+ as before).
+ 2. Use a platform device and set the platform data. The parameters can then
+ be set through that platform data. An example of doing that is:
+
+#include <linux/ramoops.h>
+[...]
+
+static struct ramoops_platform_data ramoops_data = {
+        .mem_size               = <...>,
+        .mem_address            = <...>,
+        .record_size            = <...>,
+        .dump_oops              = <...>,
+};
+
+static struct platform_device ramoops_dev = {
+        .name = "ramoops",
+        .dev = {
+                .platform_data = &ramoops_data,
+        },
+};
+
+[... inside a function ...]
+int ret;
+
+ret = platform_device_register(&ramoops_dev);
+if (ret) {
+	printk(KERN_ERR "unable to register platform device\n");
+	return ret;
+}
+
+3. Dump format
+
+The data dump begins with a header, currently defined at "====" followed by a
+timestamp and then continues with the actual dump data.
+
+4. Reading the data
+
+The dump data can be read from memory (through /dev/mem or other means).
+Getting the module parameters, which are needed in order to parse the data can
+be done through /sys/module/ramoops/parameters/* .
-- 
1.7.2.3

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