Documentation/arm/msm/msm_ipc_logging.txt - kernel/msm.git - Git at Google

 Introduction
 ============

 This module will be used to log the events by any module/driver which
 enables Inter Processor Communication (IPC). Some of the IPC drivers such
 as Message Routers, Multiplexers etc. which act as a passive pipe need
 some mechanism to log their events. Since all such IPC drivers handle a
 large amount of traffic/events, using kernel logs renders kernel logs
 unusable by other drivers and also degrades the performance of IPC
 drivers. This new module will help in logging such high frequency IPC
 driver events while keeping the standard kernel logging mechanism
 intact.

 Hardware description
 ====================

 This module does not drive any hardware resource and will only use the
 kernel memory-space to log the events.

 Software description
 ====================

 Design Goals
 ------------
 This module is designed to
 	* support logging for drivers handling large amount of
 	  traffic/events
 	* define & differentiate events/logs from different drivers
 	* support both id-based and stream-based logging
 	* support extracting the logs from both live target & memory dump

 IPC Log Context
 ----------------

 This module will support logging by multiple drivers. To differentiate
 between the multiple drivers that are using this logging mechanism, each
 driver will be assigned a unique context by this module. Associated with
 each context is the logging space, dynamically allocated from the kernel
 memory-space, specific to that context so that the events logged using that
 context will not interfere with other contexts.

 Event Logging
 --------------

 Every event will be logged as a <Type: Size: Value> combination. Type
 field identifies the type of the event that is logged. Size field represents
 the size of the log information. Value field represents the actual
 information being logged. This approach will support both id-based logging
 and stream-based logging. This approach will also support logging sub-events
 of an event. This module will provide helper routines to encode/decode the
 logs to/from this format.

 Encode Context
 ---------------

 Encode context is a temporary storage space that will be used by the client
 drivers to log the events in <Type: Size: Value> format. The client drivers
 will perform an encode start operation to initialize the encode context
 data structure. Then the client drivers will log their events into the
 encode context. Upon completion of event logging, the client drivers will
 perform an encode end operation to finalize the encode context data
 structure to be logged. Then this updated encode context data structure
 will be written into the client driver's IPC Log Context. The maximum
 event log size will be defined as 256 bytes.

 Log Space
 ----------

 Each context (Figure 1) has an associated log space, which is dynamically
 allocated from the kernel memory-space. The log space is organized as a list of
 1 or more kernel memory pages. Each page (Figure 2) contains header information
 which is used to differentiate the log kernel page from the other kernel pages.


       0 ---------------------------------
         |     magic_no = 0x25874452     |
         ---------------------------------
         |    nmagic_no = 0x52784425     |
         ---------------------------------
         |            version            |
         ---------------------------------
         |          user_version         |
         ---------------------------------
         |            log_id             |
         ---------------------------------
         |          header_size          |
         ---------------------------------
         |                               |
         |                               |
         |       name [20 chars]         |
         |                               |
         |                               |
         ---------------------------------
         |    run-time data structures   |
         ---------------------------------
          Figure 1 - Log Context Structure


         31                             0
       0 ---------------------------------
         |     magic_no = 0x52784425     |
         ---------------------------------
         |    nmagic_no = 0xAD87BBDA     |
         ---------------------------------
         |1|         page_num            |
         ---------------------------------
         |  read_offset  | write_offset  |
         ---------------------------------
         |            log_id             |
         ---------------------------------
         |     start_time low word       |
         |     start_time high word      |
         ---------------------------------
         |       end_time low word       |
         |       end_time high word      |
         ---------------------------------
         |         context offset        |
         ---------------------------------
         |    run-time data structures   |
         .            . . .              .
         ---------------------------------
         |                               |
         |           Log Data            |
         .              .                .
         .              .                .
         |                               |
         --------------------------------- PAGE_SIZE - 1
             Figure 2 - Log Page Structure

 In addition to extracting logs at runtime through DebugFS, IPC Logging has been
 designed to allow extraction of logs from a memory dump.  The magic numbers,
 timestamps, and context offset are all added to support the memory-dump
 extraction use case.

 Design
 ======

 Alternate solutions discussed include using kernel & SMEM logs which are
 limited in size and hence using them render them unusable by other drivers.
 Also kernel logging into serial console is slowing down the performance of
 the drivers by multiple times and sometimes lead to APPs watchdog bite.

 Power Management
 ================

 Not-Applicable

 SMP/multi-core
 ==============

 This module uses spinlocks & mutexes to handle multi-core safety.

 Security
 ========

 Not-Applicable

 Performance
 ===========

 This logging mechanism, based on experimental data, is not expected to
 cause a significant performance degradation. Under worst case, it can
 cause 1 - 2 percent degradation in the throughput of the IPC Drivers.

 Interface
 =========

 Exported Data Structures
 ------------------------
 struct encode_context {
 	struct tsv_header hdr;
 	char buff[MAX_MSG_SIZE];
 	int offset;
 };

 struct decode_context {
 	int output_format;
 	char *buff;
 	int size;
 };

 Kernel-Space Interface APIs
 ----------------------------
 /*
  * ipc_log_context_create: Create a ipc log context
  *
  * @max_num_pages: Number of pages of logging space required (max. 10)
  * @mod_name     : Name of the directory entry under DEBUGFS
  * @user_version : Version number of user-defined message formats
  *
  * returns reference to context on success, NULL on failure
  */
 void * ipc_log_context_create(int max_num_pages,
 			      const char *mod_name);

 /*
  * msg_encode_start: Start encoding a log message
  *
  * @ectxt: Temporary storage to hold the encoded message
  * @type:  Root event type defined by the module which is logging
  */
 void msg_encode_start(struct encode_context *ectxt, uint32_t type);

 /*
  * msg_encode_end: Complete the message encode process
  *
  * @ectxt: Temporary storage which holds the encoded message
  */
 void msg_encode_end(struct encode_context *ectxt);

 /*
  * tsv_timestamp_write: Writes the current timestamp count
  *
  * @ectxt: Context initialized by calling msg_encode_start()
  *
  * Returns 0 on success, -ve error code on failure
  */
 int tsv_timestamp_write(struct encode_context *ectxt);

 /*
  * tsv_pointer_write: Writes a data pointer
  *
  * @ectxt:   Context initialized by calling msg_encode_start()
  * @pointer: Pointer value to write
  *
  * Returns 0 on success, -ve error code on failure
  */
 int tsv_pointer_write(struct encode_context *ectxt, void *pointer);

 /*
  * tsv_int32_write: Writes a 32-bit integer value
  *
  * @ectxt: Context initialized by calling msg_encode_start()
  * @n:     Integer to write
  *
  * Returns 0 on success, -ve error code on failure
  */
 int tsv_int32_write(struct encode_context *ectxt, int32_t n);

 /*
  * tsv_byte_array_write: Writes a byte array
  *
  * @ectxt: Context initialized by calling msg_encode_start()
  * @data:  Location of data
  * @data_size: Size of data to be written
  *
  * Returns 0 on success, -ve error code on failure
  */
 int tsv_byte_array_write(struct encode_context *ectxt,
 			  void *data, int data_size);

 /*
  * ipc_log_write: Write the encoded message into the log space
  *
  * @ctxt: IPC log context where the message has to be logged into
  * @ectxt: Temporary storage containing the encoded message
  */
 void ipc_log_write(unsigned long ctxt, struct encode_context *ectxt);

 /*
  * ipc_log_string: Helper function to log a string
  *
  * @dlctxt: IPC Log Context created using ipc_log_context_create()
  * @fmt:    Data specified using format specifiers
  */
 int ipc_log_string(unsigned long dlctxt, const char *fmt, ...);

 /*
  * tsv_timestamp_read: Reads a timestamp
  *
  * @ectxt:  Context retrieved by reading from log space
  * @dctxt:  Temporary storage to hold the decoded message
  * @format: Output format while dumping through DEBUGFS
  */
 void tsv_timestamp_read(struct encode_context *ectxt,
 			struct decode_context *dctxt, const char *format);

 /*
  * tsv_pointer_read: Reads a data pointer
  *
  * @ectxt:  Context retrieved by reading from log space
  * @dctxt:  Temporary storage to hold the decoded message
  * @format: Output format while dumping through DEBUGFS
  */
 void tsv_pointer_read(struct encode_context *ectxt,
 		      struct decode_context *dctxt, const char *format);

 /*
  * tsv_int32_read: Reads a 32-bit integer value
  *
  * @ectxt:  Context retrieved by reading from log space
  * @dctxt:  Temporary storage to hold the decoded message
  * @format: Output format while dumping through DEBUGFS
  */
 void tsv_int32_read(struct encode_context *ectxt,
 		    struct decode_context *dctxt, const char *format);

 /*
  * tsv_byte_array_read: Reads a byte array/string
  *
  * @ectxt:  Context retrieved by reading from log space
  * @dctxt:  Temporary storage to hold the decoded message
  * @format: Output format while dumping through DEBUGFS
  */
 void tsv_byte_array_read(struct encode_context *ectxt,
 			 struct decode_context *dctxt, const char *format);

 /*
  * add_deserialization_func: Register a deserialization function to
  *                           to unpack the subevents of a main event
  *
  * @ctxt: IPC log context to which the deserialization function has
  *        to be registered
  * @type: Main/Root event, defined by the module which is logging, to
  *        which this deserialization function has to be registered.
  * @dfune: Deserialization function to be registered
  *
  * return 0 on success, -ve value on FAILURE
  */
 int add_deserialization_func(unsigned long ctxt, int type,
 			void (*dfunc)(struct encode_context *,
 				      struct decode_context *));

 Driver parameters
 =================

 Not-Applicable

 Config options
 ==============

 Not-Applicable

 Dependencies
 ============

 This module will partially depend on CONFIG_DEBUGFS, in order to dump the
 logs through debugfs. If CONFIG_DEBUGFS is disabled, the above mentioned
 helper functions will perform no operation and return appropriate error
 code if the return value is non void. Under such circumstances the logs can
 only be extracted through the memory dump.

 User space utilities
 ====================

 DEBUGFS

 Other
 =====

 Not-Applicable

 Known issues
 ============

 None

 To do
 =====

 None
	Introduction
	============

	This module will be used to log the events by any module/driver which
	enables Inter Processor Communication (IPC). Some of the IPC drivers such
	as Message Routers, Multiplexers etc. which act as a passive pipe need
	some mechanism to log their events. Since all such IPC drivers handle a
	large amount of traffic/events, using kernel logs renders kernel logs
	unusable by other drivers and also degrades the performance of IPC
	drivers. This new module will help in logging such high frequency IPC
	driver events while keeping the standard kernel logging mechanism
	intact.

	Hardware description
	====================

	This module does not drive any hardware resource and will only use the
	kernel memory-space to log the events.

	Software description
	====================

	Design Goals
	------------
	This module is designed to
	* support logging for drivers handling large amount of
	traffic/events
	* define & differentiate events/logs from different drivers
	* support both id-based and stream-based logging
	* support extracting the logs from both live target & memory dump

	IPC Log Context
	----------------

	This module will support logging by multiple drivers. To differentiate
	between the multiple drivers that are using this logging mechanism, each
	driver will be assigned a unique context by this module. Associated with
	each context is the logging space, dynamically allocated from the kernel
	memory-space, specific to that context so that the events logged using that
	context will not interfere with other contexts.

	Event Logging
	--------------

	Every event will be logged as a <Type: Size: Value> combination. Type
	field identifies the type of the event that is logged. Size field represents
	the size of the log information. Value field represents the actual
	information being logged. This approach will support both id-based logging
	and stream-based logging. This approach will also support logging sub-events
	of an event. This module will provide helper routines to encode/decode the
	logs to/from this format.

	Encode Context
	---------------

	Encode context is a temporary storage space that will be used by the client
	drivers to log the events in <Type: Size: Value> format. The client drivers
	will perform an encode start operation to initialize the encode context
	data structure. Then the client drivers will log their events into the
	encode context. Upon completion of event logging, the client drivers will
	perform an encode end operation to finalize the encode context data
	structure to be logged. Then this updated encode context data structure
	will be written into the client driver's IPC Log Context. The maximum
	event log size will be defined as 256 bytes.

	Log Space
	----------

	Each context (Figure 1) has an associated log space, which is dynamically
	allocated from the kernel memory-space. The log space is organized as a list of
	1 or more kernel memory pages. Each page (Figure 2) contains header information
	which is used to differentiate the log kernel page from the other kernel pages.


	0 ---------------------------------
	\| magic_no = 0x25874452 \|
	---------------------------------
	\| nmagic_no = 0x52784425 \|
	---------------------------------
	\| version \|
	---------------------------------
	\| user_version \|
	---------------------------------
	\| log_id \|
	---------------------------------
	\| header_size \|
	---------------------------------
	\| \|
	\| \|
	\| name [20 chars] \|
	\| \|
	\| \|
	---------------------------------
	\| run-time data structures \|
	---------------------------------
	Figure 1 - Log Context Structure


	31 0
	0 ---------------------------------
	\| magic_no = 0x52784425 \|
	---------------------------------
	\| nmagic_no = 0xAD87BBDA \|
	---------------------------------
	\|1\| page_num \|
	---------------------------------
	\| read_offset \| write_offset \|
	---------------------------------
	\| log_id \|
	---------------------------------
	\| start_time low word \|
	\| start_time high word \|
	---------------------------------
	\| end_time low word \|
	\| end_time high word \|
	---------------------------------
	\| context offset \|
	---------------------------------
	\| run-time data structures \|
	. . . . .
	---------------------------------
	\| \|
	\| Log Data \|
	. . .
	. . .
	\| \|
	--------------------------------- PAGE_SIZE - 1
	Figure 2 - Log Page Structure

	In addition to extracting logs at runtime through DebugFS, IPC Logging has been
	designed to allow extraction of logs from a memory dump. The magic numbers,
	timestamps, and context offset are all added to support the memory-dump
	extraction use case.

	Design
	======

	Alternate solutions discussed include using kernel & SMEM logs which are
	limited in size and hence using them render them unusable by other drivers.
	Also kernel logging into serial console is slowing down the performance of
	the drivers by multiple times and sometimes lead to APPs watchdog bite.

	Power Management
	================

	Not-Applicable

	SMP/multi-core
	==============

	This module uses spinlocks & mutexes to handle multi-core safety.

	Security
	========

	Not-Applicable

	Performance
	===========

	This logging mechanism, based on experimental data, is not expected to
	cause a significant performance degradation. Under worst case, it can
	cause 1 - 2 percent degradation in the throughput of the IPC Drivers.

	Interface
	=========

	Exported Data Structures
	------------------------
	struct encode_context {
	struct tsv_header hdr;
	char buff[MAX_MSG_SIZE];
	int offset;
	};

	struct decode_context {
	int output_format;
	char *buff;
	int size;
	};

	Kernel-Space Interface APIs
	----------------------------
	/*
	* ipc_log_context_create: Create a ipc log context
	*
	* @max_num_pages: Number of pages of logging space required (max. 10)
	* @mod_name : Name of the directory entry under DEBUGFS
	* @user_version : Version number of user-defined message formats
	*
	* returns reference to context on success, NULL on failure
	*/
	void * ipc_log_context_create(int max_num_pages,
	const char *mod_name);

	/*
	* msg_encode_start: Start encoding a log message
	*
	* @ectxt: Temporary storage to hold the encoded message
	* @type: Root event type defined by the module which is logging
	*/
	void msg_encode_start(struct encode_context *ectxt, uint32_t type);

	/*
	* msg_encode_end: Complete the message encode process
	*
	* @ectxt: Temporary storage which holds the encoded message
	*/
	void msg_encode_end(struct encode_context *ectxt);

	/*
	* tsv_timestamp_write: Writes the current timestamp count
	*
	* @ectxt: Context initialized by calling msg_encode_start()
	*
	* Returns 0 on success, -ve error code on failure
	*/
	int tsv_timestamp_write(struct encode_context *ectxt);

	/*
	* tsv_pointer_write: Writes a data pointer
	*
	* @ectxt: Context initialized by calling msg_encode_start()
	* @pointer: Pointer value to write
	*
	* Returns 0 on success, -ve error code on failure
	*/
	int tsv_pointer_write(struct encode_context ectxt, void pointer);

	/*
	* tsv_int32_write: Writes a 32-bit integer value
	*
	* @ectxt: Context initialized by calling msg_encode_start()
	* @n: Integer to write
	*
	* Returns 0 on success, -ve error code on failure
	*/
	int tsv_int32_write(struct encode_context *ectxt, int32_t n);

	/*
	* tsv_byte_array_write: Writes a byte array
	*
	* @ectxt: Context initialized by calling msg_encode_start()
	* @data: Location of data
	* @data_size: Size of data to be written
	*
	* Returns 0 on success, -ve error code on failure
	*/
	int tsv_byte_array_write(struct encode_context *ectxt,
	void *data, int data_size);

	/*
	* ipc_log_write: Write the encoded message into the log space
	*
	* @ctxt: IPC log context where the message has to be logged into
	* @ectxt: Temporary storage containing the encoded message
	*/
	void ipc_log_write(unsigned long ctxt, struct encode_context *ectxt);

	/*
	* ipc_log_string: Helper function to log a string
	*
	* @dlctxt: IPC Log Context created using ipc_log_context_create()
	* @fmt: Data specified using format specifiers
	*/
	int ipc_log_string(unsigned long dlctxt, const char *fmt, ...);

	/*
	* tsv_timestamp_read: Reads a timestamp
	*
	* @ectxt: Context retrieved by reading from log space
	* @dctxt: Temporary storage to hold the decoded message
	* @format: Output format while dumping through DEBUGFS
	*/
	void tsv_timestamp_read(struct encode_context *ectxt,
	struct decode_context dctxt, const char format);

	/*
	* tsv_pointer_read: Reads a data pointer
	*
	* @ectxt: Context retrieved by reading from log space
	* @dctxt: Temporary storage to hold the decoded message
	* @format: Output format while dumping through DEBUGFS
	*/
	void tsv_pointer_read(struct encode_context *ectxt,
	struct decode_context dctxt, const char format);

	/*
	* tsv_int32_read: Reads a 32-bit integer value
	*
	* @ectxt: Context retrieved by reading from log space
	* @dctxt: Temporary storage to hold the decoded message
	* @format: Output format while dumping through DEBUGFS
	*/
	void tsv_int32_read(struct encode_context *ectxt,
	struct decode_context dctxt, const char format);

	/*
	* tsv_byte_array_read: Reads a byte array/string
	*
	* @ectxt: Context retrieved by reading from log space
	* @dctxt: Temporary storage to hold the decoded message
	* @format: Output format while dumping through DEBUGFS
	*/
	void tsv_byte_array_read(struct encode_context *ectxt,
	struct decode_context dctxt, const char format);

	/*
	* add_deserialization_func: Register a deserialization function to
	* to unpack the subevents of a main event
	*
	* @ctxt: IPC log context to which the deserialization function has
	* to be registered
	* @type: Main/Root event, defined by the module which is logging, to
	* which this deserialization function has to be registered.
	* @dfune: Deserialization function to be registered
	*
	* return 0 on success, -ve value on FAILURE
	*/
	int add_deserialization_func(unsigned long ctxt, int type,
	void (dfunc)(struct encode_context ,
	struct decode_context *));

	Driver parameters
	=================

	Not-Applicable

	Config options
	==============

	Not-Applicable

	Dependencies
	============

	This module will partially depend on CONFIG_DEBUGFS, in order to dump the
	logs through debugfs. If CONFIG_DEBUGFS is disabled, the above mentioned
	helper functions will perform no operation and return appropriate error
	code if the return value is non void. Under such circumstances the logs can
	only be extracted through the memory dump.

	User space utilities
	====================

	DEBUGFS

	Other
	=====

	Not-Applicable

	Known issues
	============

	None

	To do
	=====

	None