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Date: Sat, 6 Aug 2011 18:25:52 -0700
From: Randy Dunlap <rdunlap@xenotime.net>
To: Sergiu Iordache <sergiu@chromium.org>
Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] char drivers: ramoops documentation
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On Fri,  5 Aug 2011 16:33:49 -0700 Sergiu Iordache wrote:

> Add a documentation file describing the usage of Ramoops
> 
> Signed-off-by: Sergiu Iordache <sergiu@chromium.org>
> ---
>  Documentation/ramoops.txt |   73 +++++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 73 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..0575177
> --- /dev/null
> +++ b/Documentation/ramoops.txt
> @@ -0,0 +1,73 @@
> +Ramoops oops/panic logger
> +=========================
> +
> +Sergiu Iordache <sergiu@chromium.org>
> +
> +Updated: 5 August 2011
> +
> +0. Introduction
> +
> +Ramoops is an oops/panic logger that writes its logs to RAM before the system
> +crashes. It works by logging oopses and panics in a circular buffer. Ramoops
> +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
> +  * "mem_size" for the size. The memory size will be rounded down to a
> +  multiple of two.

     power of two.

> +
> +The memory area is divided into "record_size" chunks (also rounded down to
> +multiple of two) and each oops/panic writes a "record_size" chunk of

   power of two)

> +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 as "====" 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/* .
> -- 

---
~Randy
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