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_BUS_COMPONENT              0x00010000
      ACPI_AC_COMPONENT               0x00020000
      ACPI_BATTERY_COMPONENT          0x00040000
      ACPI_BUTTON_COMPONENT           0x00080000
      ACPI_SBS_COMPONENT              0x00100000
      ACPI_FAN_COMPONENT              0x00200000
      ACPI_PCI_COMPONENT              0x00400000
      ACPI_POWER_COMPONENT            0x00800000
      ACPI_CONTAINER_COMPONENT        0x01000000
      ACPI_SYSTEM_COMPONENT           0x02000000
      ACPI_THERMAL_COMPONENT          0x04000000
      ACPI_MEMORY_DEVICE_COMPONENT    0x08000000
      ACPI_VIDEO_COMPONENT            0x10000000
      ACPI_PROCESSOR_COMPONENT        0x20000000
  
  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/bus.c contains this:
  
      #define _COMPONENT              ACPI_BUS_COMPONENT
      ...
      ACPI_DEBUG_PRINT((ACPI_DB_INFO, "Device insertion detected
  "));
  
  To turn on this message, set the ACPI_BUS_COMPONENT bit in acpi.debug_layer
  and the ACPI_LV_INFO bit in acpi.debug_level.  (The ACPI_DEBUG_PRINT
  statement uses ACPI_DB_INFO, which is macro based on the ACPI_LV_INFO
  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 PCI and PCI interrupt routing debug messages:
  
      acpi.debug_layer=0x400000 acpi.debug_level=0x4
  
  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