Documentation/w1/w1.netlink - kernel/common - Git at Google

 Userspace communication protocol over connector [1].


 Message types.
 =============

 There are three types of messages between w1 core and userspace:
 1. Events. They are generated each time new master or slave device
 	found either due to automatic or requested search.
 2. Userspace commands.
 3. Replies to userspace commands.


 Protocol.
 ========

 [struct cn_msg] - connector header.
 	Its length field is equal to size of the attached data
 [struct w1_netlink_msg] - w1 netlink header.
 	__u8 type 	- message type.
 			W1_LIST_MASTERS
 				list current bus masters
 			W1_SLAVE_ADD/W1_SLAVE_REMOVE
 				slave add/remove events
 			W1_MASTER_ADD/W1_MASTER_REMOVE
 				master add/remove events
 			W1_MASTER_CMD
 				userspace command for bus master
 				device (search/alarm search)
 			W1_SLAVE_CMD
 				userspace command for slave device
 				(read/write/touch)
 	__u8 res	- reserved
 	__u16 len	- size of data attached to this header data
 	union {
 		__u8 id[8];			 - slave unique device id
 		struct w1_mst {
 			__u32		id;	 - master's id
 			__u32		res;	 - reserved
 		} mst;
 	} id;

 [struct w1_netlink_cmd] - command for given master or slave device.
 	__u8 cmd	- command opcode.
 			W1_CMD_READ 	- read command
 			W1_CMD_WRITE	- write command
 			W1_CMD_TOUCH	- touch command
 				(write and sample data back to userspace)
 			W1_CMD_SEARCH	- search command
 			W1_CMD_ALARM_SEARCH - alarm search command
 	__u8 res	- reserved
 	__u16 len	- length of data for this command
 		For read command data must be allocated like for write command
 	__u8 data[0]	- data for this command


 Each connector message can include one or more w1_netlink_msg with
 zero or more attached w1_netlink_cmd messages.

 For event messages there are no w1_netlink_cmd embedded structures,
 only connector header and w1_netlink_msg strucutre with "len" field
 being zero and filled type (one of event types) and id:
 either 8 bytes of slave unique id in host order,
 or master's id, which is assigned to bus master device
 when it is added to w1 core.

 Currently replies to userspace commands are only generated for read
 command request. One reply is generated exactly for one w1_netlink_cmd
 read request. Replies are not combined when sent - i.e. typical reply
 messages looks like the following:

 [cn_msg][w1_netlink_msg][w1_netlink_cmd]
 cn_msg.len = sizeof(struct w1_netlink_msg) +
 	     sizeof(struct w1_netlink_cmd) +
 	     cmd->len;
 w1_netlink_msg.len = sizeof(struct w1_netlink_cmd) + cmd->len;
 w1_netlink_cmd.len = cmd->len;

 Replies to W1_LIST_MASTERS should send a message back to the userspace
 which will contain list of all registered master ids in the following
 format:

 	cn_msg (CN_W1_IDX.CN_W1_VAL as id, len is equal to sizeof(struct
 	w1_netlink_msg) plus number of masters multiplied by 4)
 	w1_netlink_msg (type: W1_LIST_MASTERS, len is equal to
 		number of masters multiplied by 4 (u32 size))
 	id0 ... idN

 	Each message is at most 4k in size, so if number of master devices
 	exceeds this, it will be split into several messages,
 	cn.seq will be increased for each one.

 W1 search and alarm search commands.
 request:
 [cn_msg]
   [w1_netlink_msg type = W1_MASTER_CMD
   	id is equal to the bus master id to use for searching]
   [w1_netlink_cmd cmd = W1_CMD_SEARCH or W1_CMD_ALARM_SEARCH]

 reply:
   [cn_msg, ack = 1 and increasing, 0 means the last message,
   	seq is equal to the request seq]
   [w1_netlink_msg type = W1_MASTER_CMD]
   [w1_netlink_cmd cmd = W1_CMD_SEARCH or W1_CMD_ALARM_SEARCH
 	len is equal to number of IDs multiplied by 8]
   [64bit-id0 ... 64bit-idN]
 Length in each header corresponds to the size of the data behind it, so
 w1_netlink_cmd->len = N * 8; where N is number of IDs in this message.
 	Can be zero.
 w1_netlink_msg->len = sizeof(struct w1_netlink_cmd) + N * 8;
 cn_msg->len = sizeof(struct w1_netlink_msg) +
 	      sizeof(struct w1_netlink_cmd) +
 	      N*8;

 W1 reset command.
 [cn_msg]
   [w1_netlink_msg type = W1_MASTER_CMD
   	id is equal to the bus master id to use for searching]
   [w1_netlink_cmd cmd = W1_CMD_RESET]


 Command status replies.
 ======================

 Each command (either root, master or slave with or without w1_netlink_cmd
 structure) will be 'acked' by the w1 core. Format of the reply is the same
 as request message except that length parameters do not account for data
 requested by the user, i.e. read/write/touch IO requests will not contain
 data, so w1_netlink_cmd.len will be 0, w1_netlink_msg.len will be size
 of the w1_netlink_cmd structure and cn_msg.len will be equal to the sum
 of the sizeof(struct w1_netlink_msg) and sizeof(struct w1_netlink_cmd).
 If reply is generated for master or root command (which do not have
 w1_netlink_cmd attached), reply will contain only cn_msg and w1_netlink_msg
 structires.

 w1_netlink_msg.status field will carry positive error value
 (EINVAL for example) or zero in case of success.

 All other fields in every structure will mirror the same parameters in the
 request message (except lengths as described above).

 Status reply is generated for every w1_netlink_cmd embedded in the
 w1_netlink_msg, if there are no w1_netlink_cmd structures,
 reply will be generated for the w1_netlink_msg.

 All w1_netlink_cmd command structures are handled in every w1_netlink_msg,
 even if there were errors, only length mismatch interrupts message processing.


 Operation steps in w1 core when new command is received.
 =======================================================

 When new message (w1_netlink_msg) is received w1 core detects if it is
 master or slave request, according to w1_netlink_msg.type field.
 Then master or slave device is searched for.
 When found, master device (requested or those one on where slave device
 is found) is locked. If slave command is requested, then reset/select
 procedure is started to select given device.

 Then all requested in w1_netlink_msg operations are performed one by one.
 If command requires reply (like read command) it is sent on command completion.

 When all commands (w1_netlink_cmd) are processed muster device is unlocked
 and next w1_netlink_msg header processing started.


 Connector [1] specific documentation.
 ====================================

 Each connector message includes two u32 fields as "address".
 w1 uses CN_W1_IDX and CN_W1_VAL defined in include/linux/connector.h header.
 Each message also includes sequence and acknowledge numbers.
 Sequence number for event messages is appropriate bus master sequence number
 increased with each event message sent "through" this master.
 Sequence number for userspace requests is set by userspace application.
 Sequence number for reply is the same as was in request, and
 acknowledge number is set to seq+1.


 Additional documantion, source code examples.
 ============================================

 1. Documentation/connector
 2. http://www.ioremap.net/archive/w1
 This archive includes userspace application w1d.c which uses
 read/write/search commands for all master/slave devices found on the bus.
	Userspace communication protocol over connector [1].


	Message types.
	=============

	There are three types of messages between w1 core and userspace:
	1. Events. They are generated each time new master or slave device
	found either due to automatic or requested search.
	2. Userspace commands.
	3. Replies to userspace commands.


	Protocol.
	========

	[struct cn_msg] - connector header.
	Its length field is equal to size of the attached data
	[struct w1_netlink_msg] - w1 netlink header.
	__u8 type - message type.
	W1_LIST_MASTERS
	list current bus masters
	W1_SLAVE_ADD/W1_SLAVE_REMOVE
	slave add/remove events
	W1_MASTER_ADD/W1_MASTER_REMOVE
	master add/remove events
	W1_MASTER_CMD
	userspace command for bus master
	device (search/alarm search)
	W1_SLAVE_CMD
	userspace command for slave device
	(read/write/touch)
	__u8 res - reserved
	__u16 len - size of data attached to this header data
	union {
	__u8 id[8]; - slave unique device id
	struct w1_mst {
	__u32 id; - master's id
	__u32 res; - reserved
	} mst;
	} id;

	[struct w1_netlink_cmd] - command for given master or slave device.
	__u8 cmd - command opcode.
	W1_CMD_READ - read command
	W1_CMD_WRITE - write command
	W1_CMD_TOUCH - touch command
	(write and sample data back to userspace)
	W1_CMD_SEARCH - search command
	W1_CMD_ALARM_SEARCH - alarm search command
	__u8 res - reserved
	__u16 len - length of data for this command
	For read command data must be allocated like for write command
	__u8 data[0] - data for this command


	Each connector message can include one or more w1_netlink_msg with
	zero or more attached w1_netlink_cmd messages.

	For event messages there are no w1_netlink_cmd embedded structures,
	only connector header and w1_netlink_msg strucutre with "len" field
	being zero and filled type (one of event types) and id:
	either 8 bytes of slave unique id in host order,
	or master's id, which is assigned to bus master device
	when it is added to w1 core.

	Currently replies to userspace commands are only generated for read
	command request. One reply is generated exactly for one w1_netlink_cmd
	read request. Replies are not combined when sent - i.e. typical reply
	messages looks like the following:

	[cn_msg][w1_netlink_msg][w1_netlink_cmd]
	cn_msg.len = sizeof(struct w1_netlink_msg) +
	sizeof(struct w1_netlink_cmd) +
	cmd->len;
	w1_netlink_msg.len = sizeof(struct w1_netlink_cmd) + cmd->len;
	w1_netlink_cmd.len = cmd->len;

	Replies to W1_LIST_MASTERS should send a message back to the userspace
	which will contain list of all registered master ids in the following
	format:

	cn_msg (CN_W1_IDX.CN_W1_VAL as id, len is equal to sizeof(struct
	w1_netlink_msg) plus number of masters multiplied by 4)
	w1_netlink_msg (type: W1_LIST_MASTERS, len is equal to
	number of masters multiplied by 4 (u32 size))
	id0 ... idN

	Each message is at most 4k in size, so if number of master devices
	exceeds this, it will be split into several messages,
	cn.seq will be increased for each one.

	W1 search and alarm search commands.
	request:
	[cn_msg]
	[w1_netlink_msg type = W1_MASTER_CMD
	id is equal to the bus master id to use for searching]
	[w1_netlink_cmd cmd = W1_CMD_SEARCH or W1_CMD_ALARM_SEARCH]

	reply:
	[cn_msg, ack = 1 and increasing, 0 means the last message,
	seq is equal to the request seq]
	[w1_netlink_msg type = W1_MASTER_CMD]
	[w1_netlink_cmd cmd = W1_CMD_SEARCH or W1_CMD_ALARM_SEARCH
	len is equal to number of IDs multiplied by 8]
	[64bit-id0 ... 64bit-idN]
	Length in each header corresponds to the size of the data behind it, so
	w1_netlink_cmd->len = N * 8; where N is number of IDs in this message.
	Can be zero.
	w1_netlink_msg->len = sizeof(struct w1_netlink_cmd) + N * 8;
	cn_msg->len = sizeof(struct w1_netlink_msg) +
	sizeof(struct w1_netlink_cmd) +
	N*8;

	W1 reset command.
	[cn_msg]
	[w1_netlink_msg type = W1_MASTER_CMD
	id is equal to the bus master id to use for searching]
	[w1_netlink_cmd cmd = W1_CMD_RESET]


	Command status replies.
	======================

	Each command (either root, master or slave with or without w1_netlink_cmd
	structure) will be 'acked' by the w1 core. Format of the reply is the same
	as request message except that length parameters do not account for data
	requested by the user, i.e. read/write/touch IO requests will not contain
	data, so w1_netlink_cmd.len will be 0, w1_netlink_msg.len will be size
	of the w1_netlink_cmd structure and cn_msg.len will be equal to the sum
	of the sizeof(struct w1_netlink_msg) and sizeof(struct w1_netlink_cmd).
	If reply is generated for master or root command (which do not have
	w1_netlink_cmd attached), reply will contain only cn_msg and w1_netlink_msg
	structires.

	w1_netlink_msg.status field will carry positive error value
	(EINVAL for example) or zero in case of success.

	All other fields in every structure will mirror the same parameters in the
	request message (except lengths as described above).

	Status reply is generated for every w1_netlink_cmd embedded in the
	w1_netlink_msg, if there are no w1_netlink_cmd structures,
	reply will be generated for the w1_netlink_msg.

	All w1_netlink_cmd command structures are handled in every w1_netlink_msg,
	even if there were errors, only length mismatch interrupts message processing.


	Operation steps in w1 core when new command is received.
	=======================================================

	When new message (w1_netlink_msg) is received w1 core detects if it is
	master or slave request, according to w1_netlink_msg.type field.
	Then master or slave device is searched for.
	When found, master device (requested or those one on where slave device
	is found) is locked. If slave command is requested, then reset/select
	procedure is started to select given device.

	Then all requested in w1_netlink_msg operations are performed one by one.
	If command requires reply (like read command) it is sent on command completion.

	When all commands (w1_netlink_cmd) are processed muster device is unlocked
	and next w1_netlink_msg header processing started.


	Connector [1] specific documentation.
	====================================

	Each connector message includes two u32 fields as "address".
	w1 uses CN_W1_IDX and CN_W1_VAL defined in include/linux/connector.h header.
	Each message also includes sequence and acknowledge numbers.
	Sequence number for event messages is appropriate bus master sequence number
	increased with each event message sent "through" this master.
	Sequence number for userspace requests is set by userspace application.
	Sequence number for reply is the same as was in request, and
	acknowledge number is set to seq+1.


	Additional documantion, source code examples.
	============================================

	1. Documentation/connector
	2. http://www.ioremap.net/archive/w1
	This archive includes userspace application w1d.c which uses
	read/write/search commands for all master/slave devices found on the bus.