1Userspace communication protocol over connector [1].
2
3
4Message types.
5=============
6
7There are three types of messages between w1 core and userspace:
81. Events. They are generated each time new master or slave device
9	found either due to automatic or requested search.
102. Userspace commands.
113. Replies to userspace commands.
12
13
14Protocol.
15========
16
17[struct cn_msg] - connector header.
18	Its length field is equal to size of the attached data
19[struct w1_netlink_msg] - w1 netlink header.
20	__u8 type 	- message type.
21			W1_LIST_MASTERS
22				list current bus masters
23			W1_SLAVE_ADD/W1_SLAVE_REMOVE
24				slave add/remove events
25			W1_MASTER_ADD/W1_MASTER_REMOVE
26				master add/remove events
27			W1_MASTER_CMD
28				userspace command for bus master
29				device (search/alarm search)
30			W1_SLAVE_CMD
31				userspace command for slave device
32				(read/write/touch)
33	__u8 res	- reserved
34	__u16 len	- size of data attached to this header data
35	union {
36		__u8 id[8];			 - slave unique device id
37		struct w1_mst {
38			__u32		id;	 - master's id
39			__u32		res;	 - reserved
40		} mst;
41	} id;
42
43[struct w1_netlink_cmd] - command for given master or slave device.
44	__u8 cmd	- command opcode.
45			W1_CMD_READ 	- read command
46			W1_CMD_WRITE	- write command
47			W1_CMD_TOUCH	- touch command
48				(write and sample data back to userspace)
49			W1_CMD_SEARCH	- search command
50			W1_CMD_ALARM_SEARCH - alarm search command
51	__u8 res	- reserved
52	__u16 len	- length of data for this command
53		For read command data must be allocated like for write command
54	__u8 data[0]	- data for this command
55
56
57Each connector message can include one or more w1_netlink_msg with
58zero or more attached w1_netlink_cmd messages.
59
60For event messages there are no w1_netlink_cmd embedded structures,
61only connector header and w1_netlink_msg strucutre with "len" field
62being zero and filled type (one of event types) and id:
63either 8 bytes of slave unique id in host order,
64or master's id, which is assigned to bus master device
65when it is added to w1 core.
66
67Currently replies to userspace commands are only generated for read
68command request. One reply is generated exactly for one w1_netlink_cmd
69read request. Replies are not combined when sent - i.e. typical reply
70messages looks like the following:
71
72[cn_msg][w1_netlink_msg][w1_netlink_cmd]
73cn_msg.len = sizeof(struct w1_netlink_msg) +
74	     sizeof(struct w1_netlink_cmd) +
75	     cmd->len;
76w1_netlink_msg.len = sizeof(struct w1_netlink_cmd) + cmd->len;
77w1_netlink_cmd.len = cmd->len;
78
79Replies to W1_LIST_MASTERS should send a message back to the userspace
80which will contain list of all registered master ids in the following
81format:
82
83	cn_msg (CN_W1_IDX.CN_W1_VAL as id, len is equal to sizeof(struct
84	w1_netlink_msg) plus number of masters multiplied by 4)
85	w1_netlink_msg (type: W1_LIST_MASTERS, len is equal to
86		number of masters multiplied by 4 (u32 size))
87	id0 ... idN
88
89	Each message is at most 4k in size, so if number of master devices
90	exceeds this, it will be split into several messages,
91	cn.seq will be increased for each one.
92
93W1 search and alarm search commands.
94request:
95[cn_msg]
96  [w1_netlink_msg type = W1_MASTER_CMD
97  	id is equal to the bus master id to use for searching]
98  [w1_netlink_cmd cmd = W1_CMD_SEARCH or W1_CMD_ALARM_SEARCH]
99
100reply:
101  [cn_msg, ack = 1 and increasing, 0 means the last message,
102  	seq is equal to the request seq]
103  [w1_netlink_msg type = W1_MASTER_CMD]
104  [w1_netlink_cmd cmd = W1_CMD_SEARCH or W1_CMD_ALARM_SEARCH
105	len is equal to number of IDs multiplied by 8]
106  [64bit-id0 ... 64bit-idN]
107Length in each header corresponds to the size of the data behind it, so
108w1_netlink_cmd->len = N * 8; where N is number of IDs in this message.
109	Can be zero.
110w1_netlink_msg->len = sizeof(struct w1_netlink_cmd) + N * 8;
111cn_msg->len = sizeof(struct w1_netlink_msg) +
112	      sizeof(struct w1_netlink_cmd) +
113	      N*8;
114
115W1 reset command.
116[cn_msg]
117  [w1_netlink_msg type = W1_MASTER_CMD
118  	id is equal to the bus master id to use for searching]
119  [w1_netlink_cmd cmd = W1_CMD_RESET]
120
121
122Command status replies.
123======================
124
125Each command (either root, master or slave with or without w1_netlink_cmd
126structure) will be 'acked' by the w1 core. Format of the reply is the same
127as request message except that length parameters do not account for data
128requested by the user, i.e. read/write/touch IO requests will not contain
129data, so w1_netlink_cmd.len will be 0, w1_netlink_msg.len will be size
130of the w1_netlink_cmd structure and cn_msg.len will be equal to the sum
131of the sizeof(struct w1_netlink_msg) and sizeof(struct w1_netlink_cmd).
132If reply is generated for master or root command (which do not have
133w1_netlink_cmd attached), reply will contain only cn_msg and w1_netlink_msg
134structires.
135
136w1_netlink_msg.status field will carry positive error value
137(EINVAL for example) or zero in case of success.
138
139All other fields in every structure will mirror the same parameters in the
140request message (except lengths as described above).
141
142Status reply is generated for every w1_netlink_cmd embedded in the
143w1_netlink_msg, if there are no w1_netlink_cmd structures,
144reply will be generated for the w1_netlink_msg.
145
146All w1_netlink_cmd command structures are handled in every w1_netlink_msg,
147even if there were errors, only length mismatch interrupts message processing.
148
149
150Operation steps in w1 core when new command is received.
151=======================================================
152
153When new message (w1_netlink_msg) is received w1 core detects if it is
154master or slave request, according to w1_netlink_msg.type field.
155Then master or slave device is searched for.
156When found, master device (requested or those one on where slave device
157is found) is locked. If slave command is requested, then reset/select
158procedure is started to select given device.
159
160Then all requested in w1_netlink_msg operations are performed one by one.
161If command requires reply (like read command) it is sent on command completion.
162
163When all commands (w1_netlink_cmd) are processed muster device is unlocked
164and next w1_netlink_msg header processing started.
165
166
167Connector [1] specific documentation.
168====================================
169
170Each connector message includes two u32 fields as "address".
171w1 uses CN_W1_IDX and CN_W1_VAL defined in include/linux/connector.h header.
172Each message also includes sequence and acknowledge numbers.
173Sequence number for event messages is appropriate bus master sequence number
174increased with each event message sent "through" this master.
175Sequence number for userspace requests is set by userspace application.
176Sequence number for reply is the same as was in request, and
177acknowledge number is set to seq+1.
178
179
180Additional documantion, source code examples.
181============================================
182
1831. Documentation/connector
1842. http://www.ioremap.net/archive/w1
185This archive includes userspace application w1d.c which uses
186read/write/search commands for all master/slave devices found on the bus.
187