1===============================================
2Userspace communication protocol over connector
3===============================================
4
5Message types
6=============
7
8There are three types of messages between w1 core and userspace:
9
101. Events. They are generated each time a new master or slave device
11   is found either due to automatic or requested search.
122. Userspace commands.
133. Replies to userspace commands.
14
15
16Protocol
17========
18
19::
20
21  [struct cn_msg] - connector header.
22	Its length field is equal to size of the attached data
23  [struct w1_netlink_msg] - w1 netlink header.
24	__u8 type 	- message type.
25			W1_LIST_MASTERS
26				list current bus masters
27			W1_SLAVE_ADD/W1_SLAVE_REMOVE
28				slave add/remove events
29			W1_MASTER_ADD/W1_MASTER_REMOVE
30				master add/remove events
31			W1_MASTER_CMD
32				userspace command for bus master
33				device (search/alarm search)
34			W1_SLAVE_CMD
35				userspace command for slave device
36				(read/write/touch)
37	__u8 status	- error indication from kernel
38	__u16 len	- size of data attached to this header data
39	union {
40		__u8 id[8];			 - slave unique device id
41		struct w1_mst {
42			__u32		id;	 - master's id
43			__u32		res;	 - reserved
44		} mst;
45	} id;
46
47  [struct w1_netlink_cmd] - command for given master or slave device.
48	__u8 cmd	- command opcode.
49			W1_CMD_READ 	- read command
50			W1_CMD_WRITE	- write command
51			W1_CMD_SEARCH	- search command
52			W1_CMD_ALARM_SEARCH - alarm search command
53			W1_CMD_TOUCH	- touch command
54				(write and sample data back to userspace)
55			W1_CMD_RESET	- send bus reset
56			W1_CMD_SLAVE_ADD	- add slave to kernel list
57			W1_CMD_SLAVE_REMOVE	- remove slave from kernel list
58			W1_CMD_LIST_SLAVES	- get slaves list from kernel
59	__u8 res	- reserved
60	__u16 len	- length of data for this command
61		For read command data must be allocated like for write command
62	__u8 data[0]	- data for this command
63
64
65Each connector message can include one or more w1_netlink_msg with
66zero or more attached w1_netlink_cmd messages.
67
68For event messages there are no w1_netlink_cmd embedded structures,
69only connector header and w1_netlink_msg structure with "len" field
70being zero and filled type (one of event types) and id:
71either 8 bytes of slave unique id in host order,
72or master's id, which is assigned to bus master device
73when it is added to w1 core.
74
75Currently replies to userspace commands are only generated for read
76command request. One reply is generated exactly for one w1_netlink_cmd
77read request. Replies are not combined when sent - i.e. typical reply
78messages looks like the following::
79
80  [cn_msg][w1_netlink_msg][w1_netlink_cmd]
81  cn_msg.len = sizeof(struct w1_netlink_msg) +
82	     sizeof(struct w1_netlink_cmd) +
83	     cmd->len;
84  w1_netlink_msg.len = sizeof(struct w1_netlink_cmd) + cmd->len;
85  w1_netlink_cmd.len = cmd->len;
86
87Replies to W1_LIST_MASTERS should send a message back to the userspace
88which will contain list of all registered master ids in the following
89format::
90
91	cn_msg (CN_W1_IDX.CN_W1_VAL as id, len is equal to sizeof(struct
92	w1_netlink_msg) plus number of masters multiplied by 4)
93	w1_netlink_msg (type: W1_LIST_MASTERS, len is equal to
94		number of masters multiplied by 4 (u32 size))
95	id0 ... idN
96
97Each message is at most 4k in size, so if number of master devices
98exceeds this, it will be split into several messages.
99
100W1 search and alarm search commands.
101
102request::
103
104  [cn_msg]
105    [w1_netlink_msg type = W1_MASTER_CMD
106	id is equal to the bus master id to use for searching]
107    [w1_netlink_cmd cmd = W1_CMD_SEARCH or W1_CMD_ALARM_SEARCH]
108
109reply::
110
111  [cn_msg, ack = 1 and increasing, 0 means the last message,
112	seq is equal to the request seq]
113  [w1_netlink_msg type = W1_MASTER_CMD]
114  [w1_netlink_cmd cmd = W1_CMD_SEARCH or W1_CMD_ALARM_SEARCH
115	len is equal to number of IDs multiplied by 8]
116  [64bit-id0 ... 64bit-idN]
117
118Length in each header corresponds to the size of the data behind it, so
119w1_netlink_cmd->len = N * 8; where N is number of IDs in this message.
120Can be zero.
121
122::
123
124  w1_netlink_msg->len = sizeof(struct w1_netlink_cmd) + N * 8;
125  cn_msg->len = sizeof(struct w1_netlink_msg) +
126	      sizeof(struct w1_netlink_cmd) +
127	      N*8;
128
129W1 reset command::
130
131  [cn_msg]
132    [w1_netlink_msg type = W1_MASTER_CMD
133	id is equal to the bus master id to use for searching]
134    [w1_netlink_cmd cmd = W1_CMD_RESET]
135
136
137Command status replies
138======================
139
140Each command (either root, master or slave with or without w1_netlink_cmd
141structure) will be 'acked' by the w1 core. Format of the reply is the same
142as request message except that length parameters do not account for data
143requested by the user, i.e. read/write/touch IO requests will not contain
144data, so w1_netlink_cmd.len will be 0, w1_netlink_msg.len will be size
145of the w1_netlink_cmd structure and cn_msg.len will be equal to the sum
146of the sizeof(struct w1_netlink_msg) and sizeof(struct w1_netlink_cmd).
147If reply is generated for master or root command (which do not have
148w1_netlink_cmd attached), reply will contain only cn_msg and w1_netlink_msg
149structures.
150
151w1_netlink_msg.status field will carry positive error value
152(EINVAL for example) or zero in case of success.
153
154All other fields in every structure will mirror the same parameters in the
155request message (except lengths as described above).
156
157Status reply is generated for every w1_netlink_cmd embedded in the
158w1_netlink_msg, if there are no w1_netlink_cmd structures,
159reply will be generated for the w1_netlink_msg.
160
161All w1_netlink_cmd command structures are handled in every w1_netlink_msg,
162even if there were errors, only length mismatch interrupts message processing.
163
164
165Operation steps in w1 core when new command is received
166=======================================================
167
168When new message (w1_netlink_msg) is received w1 core detects if it is
169master or slave request, according to w1_netlink_msg.type field.
170Then master or slave device is searched for.
171When found, master device (requested or those one on where slave device
172is found) is locked. If slave command is requested, then reset/select
173procedure is started to select given device.
174
175Then all requested in w1_netlink_msg operations are performed one by one.
176If command requires reply (like read command) it is sent on command completion.
177
178When all commands (w1_netlink_cmd) are processed master device is unlocked
179and next w1_netlink_msg header processing started.
180
181
182Connector [1] specific documentation
183====================================
184
185Each connector message includes two u32 fields as "address".
186w1 uses CN_W1_IDX and CN_W1_VAL defined in include/linux/connector.h header.
187Each message also includes sequence and acknowledge numbers.
188Sequence number for event messages is appropriate bus master sequence number
189increased with each event message sent "through" this master.
190Sequence number for userspace requests is set by userspace application.
191Sequence number for reply is the same as was in request, and
192acknowledge number is set to seq+1.
193
194
195Additional documentation, source code examples
196==============================================
197
1981. Documentation/driver-api/connector.rst
1992. http://www.ioremap.net/archive/w1
200
201   This archive includes userspace application w1d.c which uses
202   read/write/search commands for all master/slave devices found on the bus.
203