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+                        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\n"));
+
+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