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Diffstat (limited to 'Documentation/ramoops.txt')
| -rw-r--r-- | Documentation/ramoops.txt | 53 |
1 files changed, 48 insertions, 5 deletions
diff --git a/Documentation/ramoops.txt b/Documentation/ramoops.txt index 8fb1ba7fe7b..69b3cac4749 100644 --- a/Documentation/ramoops.txt +++ b/Documentation/ramoops.txt @@ -3,7 +3,7 @@ Ramoops oops/panic logger Sergiu Iordache <sergiu@chromium.org> -Updated: 8 August 2011 +Updated: 17 November 2011 0. Introduction @@ -30,15 +30,26 @@ 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 on restart (i.e. new dumps after the restart will overwrite old ones). +Ramoops also supports software ECC protection of persistent memory regions. +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 ramoops parameters can be done in 2 different manners: 1. Use the module parameters (which have the names of the variables described as before). + For quick debugging, you can also reserve parts of memory during 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" 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> +#include <linux/pstore_ram.h> [...] static struct ramoops_platform_data ramoops_data = { @@ -46,6 +57,7 @@ static struct ramoops_platform_data ramoops_data = { .mem_address = <...>, .record_size = <...>, .dump_oops = <...>, + .ecc = <...>, }; static struct platform_device ramoops_dev = { @@ -64,6 +76,14 @@ if (ret) { 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.: + +#include <linux/memblock.h> + +memblock_reserve(ramoops_data.mem_address, ramoops_data.mem_size); + 3. Dump format The data dump begins with a header, currently defined as "====" followed by a @@ -71,6 +91,29 @@ timestamp and a new line. The dump then continues with the actual 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/* . +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 +a stored record from RAM, simply unlink the respective pstore file. + +5. 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: + + # mount -t debugfs debugfs /sys/kernel/debug/ + # echo 1 > /sys/kernel/debug/pstore/record_ftrace + # reboot -f + [...] + # mount -t pstore pstore /mnt/ + # tail /mnt/ftrace-ramoops + 0 ffffffff8101ea64 ffffffff8101bcda native_apic_mem_read <- disconnect_bsp_APIC+0x6a/0xc0 + 0 ffffffff8101ea44 ffffffff8101bcf6 native_apic_mem_write <- disconnect_bsp_APIC+0x86/0xc0 + 0 ffffffff81020084 ffffffff8101a4b5 hpet_disable <- native_machine_shutdown+0x75/0x90 + 0 ffffffff81005f94 ffffffff8101a4bb iommu_shutdown_noop <- native_machine_shutdown+0x7b/0x90 + 0 ffffffff8101a6a1 ffffffff8101a437 native_machine_emergency_restart <- native_machine_restart+0x37/0x40 + 0 ffffffff811f9876 ffffffff8101a73a acpi_reboot <- native_machine_emergency_restart+0xaa/0x1e0 + 0 ffffffff8101a514 ffffffff8101a772 mach_reboot_fixups <- native_machine_emergency_restart+0xe2/0x1e0 + 0 ffffffff811d9c54 ffffffff8101a7a0 __const_udelay <- native_machine_emergency_restart+0x110/0x1e0 + 0 ffffffff811d9c34 ffffffff811d9c80 __delay <- __const_udelay+0x30/0x40 + 0 ffffffff811d9d14 ffffffff811d9c3f delay_tsc <- __delay+0xf/0x20 |