From b2777b650c5073010adea8ec2bb38eaad1cf800a Mon Sep 17 00:00:00 2001 From: Mauro Carvalho Chehab Date: Fri, 23 Sep 2016 15:24:07 -0300 Subject: [PATCH] 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 --- Documentation/ramoops.txt | 88 +++++++++++++++++++++------------------ 1 file changed, 48 insertions(+), 40 deletions(-) diff --git a/Documentation/ramoops.txt b/Documentation/ramoops.txt index 26b9f31cf65a..7eaf1e71c083 100644 --- a/Documentation/ramoops.txt +++ b/Documentation/ramoops.txt @@ -5,34 +5,37 @@ Sergiu Iordache Updated: 17 November 2011 -0. Introduction +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 concepts +---------------- 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). - -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 + + * ``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). + +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. -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. -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. The module uses a counter to record multiple dumps but the counter gets reset @@ -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. -2. Setting the parameters +Setting the parameters +---------------------- Setting the ramoops parameters can be done in several different manners: @@ -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:: + + mem=128M ramoops.mem_address=0x8000000 ramoops.ecc=1 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:: reserved-memory { #address-cells = <2>; @@ -73,60 +78,63 @@ Setting the ramoops parameters can be done in several different manners: }; 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:: -#include -[...] + #include + [...] -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 = <...>, -}; + }; -static struct platform_device ramoops_dev = { + static struct platform_device ramoops_dev = { .name = "ramoops", .dev = { .platform_data = &ramoops_data, }, -}; + }; -[... inside a function ...] -int ret; + [... inside a function ...] + int ret; -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; -} + } 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.:: -#include + #include -memblock_reserve(ramoops_data.mem_address, ramoops_data.mem_size); + memblock_reserve(ramoops_data.mem_address, ramoops_data.mem_size); -3. Dump format +Dump format +----------- -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. -4. Reading the data +Reading the data +---------------- 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. -5. Persistent function tracing +Persistent function tracing +--------------------------- 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:: # mount -t debugfs debugfs /sys/kernel/debug/ # echo 1 > /sys/kernel/debug/pstore/record_ftrace -- 2.20.1