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Documentation/ramoops.txt: convert it to ReST format
- Fix document title; - use quote blocks where needed; - use monotonic fonts for config options and file names; - adjust whitespaces and blank lines; - add it to the user's book. Signed-off-by: Mauro Carvalho Chehab <[email protected]>
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@@ -5,34 +5,37 @@ Sergiu Iordache <[email protected]> | |
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Updated: 17 November 2011 | ||
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0. Introduction | ||
Introduction | ||
------------ | ||
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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. | ||
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1. Ramoops concepts | ||
Ramoops concepts | ||
---------------- | ||
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Ramoops uses a predefined memory area to store the dump. The start and size | ||
and type of the memory area are set using three variables: | ||
* "mem_address" for the start | ||
* "mem_size" for the size. The memory size will be rounded down to a | ||
power of two. | ||
* "mem_type" to specifiy if the memory type (default is pgprot_writecombine). | ||
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Typically the default value of mem_type=0 should be used as that sets the pstore | ||
mapping to pgprot_writecombine. Setting mem_type=1 attempts to use | ||
pgprot_noncached, which only works on some platforms. This is because pstore | ||
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* ``mem_address`` for the start | ||
* ``mem_size`` for the size. The memory size will be rounded down to a | ||
power of two. | ||
* ``mem_type`` to specifiy if the memory type (default is pgprot_writecombine). | ||
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Typically the default value of ``mem_type=0`` should be used as that sets the pstore | ||
mapping to pgprot_writecombine. Setting ``mem_type=1`` attempts to use | ||
``pgprot_noncached``, which only works on some platforms. This is because pstore | ||
depends on atomic operations. At least on ARM, pgprot_noncached causes the | ||
memory to be mapped strongly ordered, and atomic operations on strongly ordered | ||
memory are implementation defined, and won't work on many ARMs such as omaps. | ||
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The memory area is divided into "record_size" chunks (also rounded down to | ||
power of two) and each oops/panic writes a "record_size" chunk of | ||
The memory area is divided into ``record_size`` chunks (also rounded down to | ||
power of two) and each oops/panic writes a ``record_size`` chunk of | ||
information. | ||
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Dumping both oopses and panics can be done by setting 1 in the "dump_oops" | ||
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. | ||
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The module uses a counter to record multiple dumps but the counter gets reset | ||
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@@ -43,7 +46,8 @@ This might be useful when a hardware reset was used to bring the machine back | |
to life (i.e. a watchdog triggered). In such cases, RAM may be somewhat | ||
corrupt, but usually it is restorable. | ||
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2. Setting the parameters | ||
Setting the parameters | ||
---------------------- | ||
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Setting the ramoops parameters can be done in several different manners: | ||
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@@ -52,12 +56,13 @@ Setting the ramoops parameters can be done in several different manners: | |
boot and then use the reserved memory for ramoops. For example, assuming a | ||
machine with > 128 MB of memory, the following kernel command line will tell | ||
the kernel to use only the first 128 MB of memory, and place ECC-protected | ||
ramoops region at 128 MB boundary: | ||
"mem=128M ramoops.mem_address=0x8000000 ramoops.ecc=1" | ||
ramoops region at 128 MB boundary:: | ||
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mem=128M ramoops.mem_address=0x8000000 ramoops.ecc=1 | ||
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B. Use Device Tree bindings, as described in | ||
Documentation/device-tree/bindings/reserved-memory/ramoops.txt. | ||
For example: | ||
``Documentation/device-tree/bindings/reserved-memory/ramoops.txt``. | ||
For example:: | ||
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reserved-memory { | ||
#address-cells = <2>; | ||
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}; | ||
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C. 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: | ||
be set through that platform data. An example of doing that is:: | ||
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#include <linux/pstore_ram.h> | ||
[...] | ||
#include <linux/pstore_ram.h> | ||
[...] | ||
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static struct ramoops_platform_data ramoops_data = { | ||
static struct ramoops_platform_data ramoops_data = { | ||
.mem_size = <...>, | ||
.mem_address = <...>, | ||
.mem_type = <...>, | ||
.record_size = <...>, | ||
.dump_oops = <...>, | ||
.ecc = <...>, | ||
}; | ||
}; | ||
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static struct platform_device ramoops_dev = { | ||
static struct platform_device ramoops_dev = { | ||
.name = "ramoops", | ||
.dev = { | ||
.platform_data = &ramoops_data, | ||
}, | ||
}; | ||
}; | ||
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[... inside a function ...] | ||
int ret; | ||
[... inside a function ...] | ||
int ret; | ||
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ret = platform_device_register(&ramoops_dev); | ||
if (ret) { | ||
ret = platform_device_register(&ramoops_dev); | ||
if (ret) { | ||
printk(KERN_ERR "unable to register platform device\n"); | ||
return ret; | ||
} | ||
} | ||
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You can specify either RAM memory or peripheral devices' memory. However, when | ||
specifying RAM, be sure to reserve the memory by issuing memblock_reserve() | ||
very early in the architecture code, e.g.: | ||
very early in the architecture code, e.g.:: | ||
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#include <linux/memblock.h> | ||
#include <linux/memblock.h> | ||
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memblock_reserve(ramoops_data.mem_address, ramoops_data.mem_size); | ||
memblock_reserve(ramoops_data.mem_address, ramoops_data.mem_size); | ||
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3. Dump format | ||
Dump format | ||
----------- | ||
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The data dump begins with a header, currently defined as "====" followed by a | ||
The data dump begins with a header, currently defined as ``====`` followed by a | ||
timestamp and a new line. The dump then continues with the actual data. | ||
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4. Reading the data | ||
Reading the data | ||
---------------- | ||
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The dump data can be read from the pstore filesystem. The format for these | ||
files is "dmesg-ramoops-N", where N is the record number in memory. To delete | ||
files is ``dmesg-ramoops-N``, where N is the record number in memory. To delete | ||
a stored record from RAM, simply unlink the respective pstore file. | ||
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5. Persistent function tracing | ||
Persistent function tracing | ||
--------------------------- | ||
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Persistent function tracing might be useful for debugging software or hardware | ||
related hangs. The functions call chain log is stored in a "ftrace-ramoops" | ||
file. Here is an example of usage: | ||
related hangs. The functions call chain log is stored in a ``ftrace-ramoops`` | ||
file. Here is an example of usage:: | ||
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# mount -t debugfs debugfs /sys/kernel/debug/ | ||
# echo 1 > /sys/kernel/debug/pstore/record_ftrace | ||
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