ACPICA Trace Facility

Copyright (C) 2015, Intel Corporation
Author: Lv Zheng <lv.zheng@intel.com>


Abstract:

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

1. Functionalities and usage examples:

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

   A. 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: Refer to Documentation/acpi/debug.txt for
			     possible debug layer/level masking values.
      \PPPP.AAAA.TTTT.HHHH: Full path of a control method that can be found
			    in the ACPI namespace. It needn't be an entry
			    of a control method evaluation.

   B. AML tracer

   There are special log entries added by the method tracing facility at
   the "trace points" the AML interpreter starts/stops to execute a control
   method, or an AML opcode. Note that the format of the log entries are
   subject to change:
     [    0.186427]   exdebug-0398 ex_trace_point        : Method Begin [0xf58394d8:\_SB.PCI0.LPCB.ECOK] execution.
     [    0.186630]   exdebug-0398 ex_trace_point        : Opcode Begin [0xf5905c88:If] execution.
     [    0.186820]   exdebug-0398 ex_trace_point        : Opcode Begin [0xf5905cc0:LEqual] execution.
     [    0.187010]   exdebug-0398 ex_trace_point        : Opcode Begin [0xf5905a20:-NamePath-] execution.
     [    0.187214]   exdebug-0398 ex_trace_point        : Opcode End [0xf5905a20:-NamePath-] execution.
     [    0.187407]   exdebug-0398 ex_trace_point        : Opcode Begin [0xf5905f60:One] execution.
     [    0.187594]   exdebug-0398 ex_trace_point        : Opcode End [0xf5905f60:One] execution.
     [    0.187789]   exdebug-0398 ex_trace_point        : Opcode End [0xf5905cc0:LEqual] execution.
     [    0.187980]   exdebug-0398 ex_trace_point        : Opcode Begin [0xf5905cc0:Return] execution.
     [    0.188146]   exdebug-0398 ex_trace_point        : Opcode Begin [0xf5905f60:One] execution.
     [    0.188334]   exdebug-0398 ex_trace_point        : Opcode End [0xf5905f60:One] execution.
     [    0.188524]   exdebug-0398 ex_trace_point        : Opcode End [0xf5905cc0:Return] execution.
     [    0.188712]   exdebug-0398 ex_trace_point        : Opcode End [0xf5905c88:If] execution.
     [    0.188903]   exdebug-0398 ex_trace_point        : Method End [0xf58394d8:\_SB.PCI0.LPCB.ECOK] execution.

   Developers can utilize these special log entries to track the AML
   interpretion, thus can aid issue debugging and performance tuning. Note
   that, as the "AML tracer" logs are implemented via ACPI_DEBUG_PRINT()
   macro, CONFIG_ACPI_DEBUG is also required to be enabled for enabling
   "AML tracer" logs.

   The following command examples illustrate the usage of the "AML tracer"
   functionality:
   a. Filter out the method start/stop "AML tracer" logs when control
      methods are being evaluated:
      # cd /sys/module/acpi/parameters
      # echo "0x80" > trace_debug_layer
      # echo "0x10" > trace_debug_level
      # echo "enable" > trace_state
   b. Filter out the method start/stop "AML tracer" when the specified
      control method is being evaluated:
      # cd /sys/module/acpi/parameters
      # echo "0x80" > trace_debug_layer
      # echo "0x10" > trace_debug_level
      # echo "\PPPP.AAAA.TTTT.HHHH" > trace_method_name
      # echo "method" > trace_state
   c. Filter out the method start/stop "AML tracer" logs when the specified
      control method is being evaluated for the first time:
      # cd /sys/module/acpi/parameters
      # echo "0x80" > trace_debug_layer
      # echo "0x10" > trace_debug_level
      # echo "\PPPP.AAAA.TTTT.HHHH" > trace_method_name
      # echo "method-once" > trace_state
   d. Filter out the method/opcode start/stop "AML tracer" when the
      specified control method is being evaluated:
      # cd /sys/module/acpi/parameters
      # echo "0x80" > trace_debug_layer
      # echo "0x10" > trace_debug_level
      # echo "\PPPP.AAAA.TTTT.HHHH" > trace_method_name
      # echo "opcode" > trace_state
   e. Filter out the method/opcode start/stop "AML tracer" when the
      specified control method is being evaluated for the first time:
      # cd /sys/module/acpi/parameters
      # echo "0x80" > trace_debug_layer
      # echo "0x10" > trace_debug_level
      # echo "\PPPP.AAAA.TTTT.HHHH" > trace_method_name
      # echo "opcode-opcode" > trace_state

  Note that all above method tracing facility related module parameters can
  be used as the boot parameters, for example:
      acpi.trace_debug_layer=0x80 acpi.trace_debug_level=0x10 \
      acpi.trace_method_name=\_SB.LID0._LID acpi.trace_state=opcode-once

2. Interface descriptions:

   All method tracing functions can be configured via ACPI module
   parameters that are accessible at /sys/module/acpi/parameters/:

   trace_method_name
	The full path of the AML method that the user wants to trace.
	Note that the full path shouldn't contain the trailing "_"s in its
	name segments but may contain "\" to form an absolute path.

   trace_debug_layer
	The temporary debug_layer used when the tracing feature is enabled.
	Using ACPI_EXECUTER (0x80) by default, which is the debug_layer
	used to match all "AML tracer" logs.

   trace_debug_level
	The temporary debug_level used when the tracing feature is enabled.
	Using ACPI_LV_TRACE_POINT (0x10) by default, which is the
	debug_level used to match all "AML tracer" logs.

   trace_state
	The status of the tracing feature.
	Users can enable/disable this debug tracing feature by executing
	the following command:
	    # echo string > /sys/module/acpi/parameters/trace_state
	Where "string" should be one of the following:
	"disable"
	    Disable the method tracing feature.
	"enable"
	    Enable the method tracing feature.
	    ACPICA debugging messages matching
	    "trace_debug_layer/trace_debug_level" during any method
	    execution will be logged.
	"method"
	    Enable the method tracing feature.
	    ACPICA debugging messages matching
	    "trace_debug_layer/trace_debug_level" during method execution
	    of "trace_method_name" will be logged.
	"method-once"
	    Enable the method tracing feature.
	    ACPICA debugging messages matching
	    "trace_debug_layer/trace_debug_level" during method execution
	    of "trace_method_name" will be logged only once.
	"opcode"
	    Enable the method tracing feature.
	    ACPICA debugging messages matching
	    "trace_debug_layer/trace_debug_level" during method/opcode
	    execution of "trace_method_name" will be logged.
	"opcode-once"
	    Enable the method tracing feature.
	    ACPICA debugging messages matching
	    "trace_debug_layer/trace_debug_level" during method/opcode
	    execution of "trace_method_name" will be logged only once.
	Note that, the difference between the "enable" and other feature
        enabling options are:
	1. When "enable" is specified, since
	   "trace_debug_layer/trace_debug_level" shall apply to all control
	   method evaluations, after configuring "trace_state" to "enable",
	   "trace_method_name" will be reset to NULL.
	2. When "method/opcode" is specified, if
	   "trace_method_name" is NULL when "trace_state" is configured to
	   these options, the "trace_debug_layer/trace_debug_level" will
	   apply to all control method evaluations.