xref: /freebsd/sys/contrib/device-tree/Bindings/reserved-memory/ramoops.txt (revision 2eb4d8dc723da3cf7d735a3226ae49da4c8c5dbc)

Ramoops oops/panic logger
=========================

ramoops provides persistent RAM storage for oops and panics, so they can be
recovered after a reboot. This is a child-node of "/reserved-memory", and
is named "ramoops" after the backend, rather than "pstore" which is the
subsystem.

Parts of this storage may be set aside for other persistent log buffers, such
as kernel log messages, or for optional ECC error-correction data.  The total
size of these optional buffers must fit in the reserved region.

Any remaining space will be used for a circular buffer of oops and panic
records.  These records have a configurable size, with a size of 0 indicating
that they should be disabled.

At least one of "record-size", "console-size", "ftrace-size", or "pmsg-size"
must be set non-zero, but are otherwise optional as listed below.


Required properties:

- compatible: must be "ramoops"

- reg: region of memory that is preserved between reboots


Optional properties:

- ecc-size: enables ECC support and specifies ECC buffer size in bytes
  (defaults to 0: no ECC)

- record-size: maximum size in bytes of each kmsg dump.
  (defaults to 0: disabled)

- console-size: size in bytes of log buffer reserved for kernel messages
  (defaults to 0: disabled)

- ftrace-size: size in bytes of log buffer reserved for function tracing and
  profiling (defaults to 0: disabled)

- pmsg-size: size in bytes of log buffer reserved for userspace messages
  (defaults to 0: disabled)

- mem-type: if present, sets the type of mapping is to be used to map the
  reserved region. mem-type: 0 = write-combined (default), 1 = unbuffered,
  2 = cached.

- unbuffered: deprecated, use mem_type instead. If present, and mem_type is
  not specified, it is equivalent to mem_type = 1 and uses unbuffered mappings
  to map the reserved region (defaults to buffered mappings mem_type = 0). If
  both are specified -- "mem_type" overrides "unbuffered".

- max-reason: if present, sets maximum type of kmsg dump reasons to store
  (defaults to 2: log Oopses and Panics). This can be set to INT_MAX to
  store all kmsg dumps. See include/linux/kmsg_dump.h KMSG_DUMP_* for other
  kmsg dump reason values. Setting this to 0 (KMSG_DUMP_UNDEF), means the
  reason filtering will be controlled by the printk.always_kmsg_dump boot
  param: if unset, it will be KMSG_DUMP_OOPS, otherwise KMSG_DUMP_MAX.

- no-dump-oops: deprecated, use max_reason instead. If present, and
  max_reason is not specified, it is equivalent to max_reason = 1
  (KMSG_DUMP_PANIC).

- flags: if present, pass ramoops behavioral flags (defaults to 0,
  see include/linux/pstore_ram.h RAMOOPS_FLAG_* for flag values).