Documentation/firmware-guide/acpi/method-tracing.rst

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.. SPDX-License-Identifier: GPL-2.0
.. include:: <isonum.txt>

=====================
ACPICA Trace Facility
=====================

:Copyright: |copy| 2015, Intel Corporation
:Author: Lv Zheng <lv.zheng@intel.com>


Abstract
========
This document describes the functions and the interfaces of the
method tracing facility.

Functionalities and usage examples
==================================

ACPICA provides method tracing capability. And two functions are
currently implemented using this capability.

Log reducer
-----------

ACPICA subsystem provides debugging outputs when CONFIG_ACPI_DEBUG is
enabled. The debugging messages which are deployed via
ACPI_DEBUG_PRINT() macro can be reduced at 2 levels - per-component
level (known as debug layer, configured via
/sys/module/acpi/parameters/debug_layer) and per-type level (known as
debug level, configured via /sys/module/acpi/parameters/debug_level).

But when the particular layer/level is applied to the control method
evaluations, the quantity of the debugging outputs may still be too
large to be put into the kernel log buffer. The idea thus is worked out
to only enable the particular debug layer/level (normally more detailed)
logs when the control method evaluation is started, and disable the
detailed logging when the control method evaluation is stopped.

The following command examples illustrate the usage of the "log reducer"
functionality:

a. Filter out the debug layer/level matched logs when control methods
   are being evaluated::

      # cd /sys/module/acpi/parameters
      # echo "0xXXXXXXXX" > trace_debug_layer
      # echo "0xYYYYYYYY" > trace_debug_level
      # echo "enable" > trace_state

b. Filter out the debug layer/level matched logs when the specified
   control method is being evaluated::

      # cd /sys/module/acpi/parameters
      # echo "0xXXXXXXXX" > trace_debug_layer
      # echo "0xYYYYYYYY" > trace_debug_level
      # echo "\PPPP.AAAA.TTTT.HHHH" > trace_method_name
      # echo "method" > /sys/module/acpi/parameters/trace_state

c. Filter out the debug layer/level matched logs when the specified
   control method is being evaluated for the first time::

      # cd /sys/module/acpi/parameters
      # echo "0xXXXXXXXX" > trace_debug_layer
      # echo "0xYYYYYYYY" > trace_debug_level
      # echo "\PPPP.AAAA.TTTT.HHHH" > trace_method_name
      # echo "method-once" > /sys/module/acpi/parameters/trace_state

Where:
   0xXXXXXXXX/0xYYYYYYYY

Annotation

Implementation Notes