Documentation/w1/w1.netlink

   1 Userspace communication protocol over connector [1].
   2
   3
   4 Message types.
   5 =============
   6
   7 There are three types of messages between w1 core and userspace:
   8 1. Events. They are generated each time a new master or slave device
   9         is found either due to automatic or requested search.
  10 2. Userspace commands.
  11 3. Replies to userspace commands.
  12
  13
  14 Protocol.
  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 status     - error indication from kernel
  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_SEARCH   - search command
  48                         W1_CMD_ALARM_SEARCH - alarm search command
  49                         W1_CMD_TOUCH    - touch command
  50                                 (write and sample data back to userspace)
  51                         W1_CMD_RESET    - send bus reset
  52                         W1_CMD_SLAVE_ADD        - add slave to kernel list
  53                         W1_CMD_SLAVE_REMOVE     - remove slave from kernel list
  54                         W1_CMD_LIST_SLAVES      - get slaves list from kernel
  55         __u8 res        - reserved
  56         __u16 len       - length of data for this command
  57                 For read command data must be allocated like for write command
  58         __u8 data[0]    - data for this command
  59
  60
  61 Each connector message can include one or more w1_netlink_msg with
  62 zero or more attached w1_netlink_cmd messages.
  63
  64 For event messages there are no w1_netlink_cmd embedded structures,
  65 only connector header and w1_netlink_msg strucutre with "len" field
  66 being zero and filled type (one of event types) and id:
  67 either 8 bytes of slave unique id in host order,
  68 or master's id, which is assigned to bus master device
  69 when it is added to w1 core.
  70
  71 Currently replies to userspace commands are only generated for read
  72 command request. One reply is generated exactly for one w1_netlink_cmd
  73 read request. Replies are not combined when sent - i.e. typical reply
  74 messages looks like the following:
  75
  76 [cn_msg][w1_netlink_msg][w1_netlink_cmd]
  77 cn_msg.len = sizeof(struct w1_netlink_msg) +
  78              sizeof(struct w1_netlink_cmd) +
  79              cmd->len;
  80 w1_netlink_msg.len = sizeof(struct w1_netlink_cmd) + cmd->len;
  81 w1_netlink_cmd.len = cmd->len;
  82
  83 Replies to W1_LIST_MASTERS should send a message back to the userspace
  84 which will contain list of all registered master ids in the following
  85 format:
  86
  87         cn_msg (CN_W1_IDX.CN_W1_VAL as id, len is equal to sizeof(struct
  88         w1_netlink_msg) plus number of masters multiplied by 4)
  89         w1_netlink_msg (type: W1_LIST_MASTERS, len is equal to
  90                 number of masters multiplied by 4 (u32 size))
  91         id0 ... idN
  92
  93         Each message is at most 4k in size, so if number of master devices
  94         exceeds this, it will be split into several messages.
  95
  96 W1 search and alarm search commands.
  97 request:
  98 [cn_msg]
  99   [w1_netlink_msg type = W1_MASTER_CMD
 100         id is equal to the bus master id to use for searching]
 101   [w1_netlink_cmd cmd = W1_CMD_SEARCH or W1_CMD_ALARM_SEARCH]
 102
 103 reply:
 104   [cn_msg, ack = 1 and increasing, 0 means the last message,
 105         seq is equal to the request seq]
 106   [w1_netlink_msg type = W1_MASTER_CMD]
 107   [w1_netlink_cmd cmd = W1_CMD_SEARCH or W1_CMD_ALARM_SEARCH
 108         len is equal to number of IDs multiplied by 8]
 109   [64bit-id0 ... 64bit-idN]
 110 Length in each header corresponds to the size of the data behind it, so
 111 w1_netlink_cmd->len = N * 8; where N is number of IDs in this message.
 112         Can be zero.
 113 w1_netlink_msg->len = sizeof(struct w1_netlink_cmd) + N * 8;
 114 cn_msg->len = sizeof(struct w1_netlink_msg) +
 115               sizeof(struct w1_netlink_cmd) +
 116               N*8;
 117
 118 W1 reset command.
 119 [cn_msg]
 120   [w1_netlink_msg type = W1_MASTER_CMD
 121         id is equal to the bus master id to use for searching]
 122   [w1_netlink_cmd cmd = W1_CMD_RESET]
 123
 124
 125 Command status replies.
 126 ======================
 127
 128 Each command (either root, master or slave with or without w1_netlink_cmd
 129 structure) will be 'acked' by the w1 core. Format of the reply is the same
 130 as request message except that length parameters do not account for data
 131 requested by the user, i.e. read/write/touch IO requests will not contain
 132 data, so w1_netlink_cmd.len will be 0, w1_netlink_msg.len will be size
 133 of the w1_netlink_cmd structure and cn_msg.len will be equal to the sum
 134 of the sizeof(struct w1_netlink_msg) and sizeof(struct w1_netlink_cmd).
 135 If reply is generated for master or root command (which do not have
 136 w1_netlink_cmd attached), reply will contain only cn_msg and w1_netlink_msg
 137 structures.
 138
 139 w1_netlink_msg.status field will carry positive error value
 140 (EINVAL for example) or zero in case of success.
 141
 142 All other fields in every structure will mirror the same parameters in the
 143 request message (except lengths as described above).
 144
 145 Status reply is generated for every w1_netlink_cmd embedded in the
 146 w1_netlink_msg, if there are no w1_netlink_cmd structures,
 147 reply will be generated for the w1_netlink_msg.
 148
 149 All w1_netlink_cmd command structures are handled in every w1_netlink_msg,
 150 even if there were errors, only length mismatch interrupts message processing.
 151
 152
 153 Operation steps in w1 core when new command is received.
 154 =======================================================
 155
 156 When new message (w1_netlink_msg) is received w1 core detects if it is
 157 master or slave request, according to w1_netlink_msg.type field.
 158 Then master or slave device is searched for.
 159 When found, master device (requested or those one on where slave device
 160 is found) is locked. If slave command is requested, then reset/select
 161 procedure is started to select given device.
 162
 163 Then all requested in w1_netlink_msg operations are performed one by one.
 164 If command requires reply (like read command) it is sent on command completion.
 165
 166 When all commands (w1_netlink_cmd) are processed master device is unlocked
 167 and next w1_netlink_msg header processing started.
 168
 169
 170 Connector [1] specific documentation.
 171 ====================================
 172
 173 Each connector message includes two u32 fields as "address".
 174 w1 uses CN_W1_IDX and CN_W1_VAL defined in include/linux/connector.h header.
 175 Each message also includes sequence and acknowledge numbers.
 176 Sequence number for event messages is appropriate bus master sequence number
 177 increased with each event message sent "through" this master.
 178 Sequence number for userspace requests is set by userspace application.
 179 Sequence number for reply is the same as was in request, and
 180 acknowledge number is set to seq+1.
 181
 182
 183 Additional documantion, source code examples.
 184 ============================================
 185
 186 1. Documentation/connector
 187 2. http://www.ioremap.net/archive/w1
 188 This archive includes userspace application w1d.c which uses
 189 read/write/search commands for all master/slave devices found on the bus.