.. SPDX-License-Identifier: GPL-2.0

=================
ACPI Debug Output
=================

The ACPI CA, the Linux ACPI core, and some ACPI drivers can generate debug
output.  This document describes how to use this facility.

Compile-time configuration
==========================

ACPI debug output is globally enabled by CONFIG_ACPI_DEBUG.  If this config
option is turned off, the debug messages are not even built into the
kernel.

Boot- and run-time configuration
================================

When CONFIG_ACPI_DEBUG=y, you can select the component and level of messages
you're interested in.  At boot-time, use the acpi.debug_layer and
acpi.debug_level kernel command line options.  After boot, you can use the
debug_layer and debug_level files in /sys/module/acpi/parameters/ to control
the debug messages.

debug_layer (component)
=======================

The "debug_layer" is a mask that selects components of interest, e.g., a
specific driver or part of the ACPI interpreter.  To build the debug_layer
bitmask, look for the "#define _COMPONENT" in an ACPI source file.

You can set the debug_layer mask at boot-time using the acpi.debug_layer
command line argument, and you can change it after boot by writing values
to /sys/module/acpi/parameters/debug_layer.

The possible components are defined in include/acpi/acoutput.h and
include/acpi/acpi_drivers.h.  Reading /sys/module/acpi/parameters/debug_layer
shows the supported mask values, currently these::

    ACPI_UTILITIES                  0x00000001
    ACPI_HARDWARE                   0x00000002
    ACPI_EVENTS                     0x00000004
    ACPI_TABLES                     0x00000008
    ACPI_NAMESPACE                  0x00000010
    ACPI_PARSER                     0x00000020
    ACPI_DISPATCHER                 0x00000040
    ACPI_EXECUTER                   0x00000080
    ACPI_RESOURCES                  0x00000100
    ACPI_CA_DEBUGGER                0x00000200
    ACPI_OS_SERVICES                0x00000400
    ACPI_CA_DISASSEMBLER            0x00000800
    ACPI_COMPILER                   0x00001000
    ACPI_TOOLS                      0x00002000
    ACPI_SBS_COMPONENT              0x00100000
    ACPI_FAN_COMPONENT              0x00200000
    ACPI_CONTAINER_COMPONENT        0x01000000
    ACPI_SYSTEM_COMPONENT           0x02000000
    ACPI_MEMORY_DEVICE_COMPONENT    0x08000000

debug_level
===========

The "debug_level" is a mask that selects different types of messages, e.g.,
those related to initialization, method execution, informational messages, etc.
To build debug_level, look at the level specified in an ACPI_DEBUG_PRINT()
statement.

The ACPI interpreter uses several different levels, but the Linux
ACPI core and ACPI drivers generally only use ACPI_LV_INFO.

You can set the debug_level mask at boot-time using the acpi.debug_level
command line argument, and you can change it after boot by writing values
to /sys/module/acpi/parameters/debug_level.

The possible levels are defined in include/acpi/acoutput.h.  Reading
/sys/module/acpi/parameters/debug_level shows the supported mask values,
currently these::

    ACPI_LV_INIT                    0x00000001
    ACPI_LV_DEBUG_OBJECT            0x00000002
    ACPI_LV_INFO                    0x00000004
    ACPI_LV_INIT_NAMES              0x00000020
    ACPI_LV_PARSE                   0x00000040
    ACPI_LV_LOAD                    0x00000080
    ACPI_LV_DISPATCH                0x00000100
    ACPI_LV_EXEC                    0x00000200
    ACPI_LV_NAMES                   0x00000400
    ACPI_LV_OPREGION                0x00000800
    ACPI_LV_BFIELD                  0x00001000
    ACPI_LV_TABLES                  0x00002000
    ACPI_LV_VALUES                  0x00004000
    ACPI_LV_OBJECTS                 0x00008000
    ACPI_LV_RESOURCES               0x00010000
    ACPI_LV_USER_REQUESTS           0x00020000
    ACPI_LV_PACKAGE                 0x00040000
    ACPI_LV_ALLOCATIONS             0x00100000
    ACPI_LV_FUNCTIONS               0x00200000
    ACPI_LV_OPTIMIZATIONS           0x00400000
    ACPI_LV_MUTEX                   0x01000000
    ACPI_LV_THREADS                 0x02000000
    ACPI_LV_IO                      0x04000000
    ACPI_LV_INTERRUPTS              0x08000000
    ACPI_LV_AML_DISASSEMBLE         0x10000000
    ACPI_LV_VERBOSE_INFO            0x20000000
    ACPI_LV_FULL_TABLES             0x40000000
    ACPI_LV_EVENTS                  0x80000000

Examples
========

For example, drivers/acpi/acpica/evxfevnt.c contains this::

    #define _COMPONENT          ACPI_EVENTS
    ...
    ACPI_DEBUG_PRINT((ACPI_DB_INIT, "ACPI mode disabled\n"));

To turn on this message, set the ACPI_EVENTS bit in acpi.debug_layer
and the ACPI_LV_INIT bit in acpi.debug_level.  (The ACPI_DEBUG_PRINT
statement uses ACPI_DB_INIT, which is a macro based on the ACPI_LV_INIT
definition.)

Enable all AML "Debug" output (stores to the Debug object while interpreting
AML) during boot::

    acpi.debug_layer=0xffffffff acpi.debug_level=0x2

Enable all ACPI hardware-related messages::

    acpi.debug_layer=0x2 acpi.debug_level=0xffffffff

Enable all ACPI_DB_INFO messages after boot::

    # echo 0x4 > /sys/module/acpi/parameters/debug_level

Show all valid component values::

    # cat /sys/module/acpi/parameters/debug_layer