203 lines
7.1 KiB
ReStructuredText
203 lines
7.1 KiB
ReStructuredText
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===============================================
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Userspace communication protocol over connector
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===============================================
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Message types
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=============
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There are three types of messages between w1 core and userspace:
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1. Events. They are generated each time a new master or slave device
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is found either due to automatic or requested search.
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2. Userspace commands.
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3. Replies to userspace commands.
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Protocol
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========
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::
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[struct cn_msg] - connector header.
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Its length field is equal to size of the attached data
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[struct w1_netlink_msg] - w1 netlink header.
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__u8 type - message type.
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W1_LIST_MASTERS
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list current bus masters
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W1_SLAVE_ADD/W1_SLAVE_REMOVE
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slave add/remove events
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W1_MASTER_ADD/W1_MASTER_REMOVE
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master add/remove events
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W1_MASTER_CMD
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userspace command for bus master
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device (search/alarm search)
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W1_SLAVE_CMD
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userspace command for slave device
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(read/write/touch)
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__u8 status - error indication from kernel
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__u16 len - size of data attached to this header data
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union {
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__u8 id[8]; - slave unique device id
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struct w1_mst {
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__u32 id; - master's id
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__u32 res; - reserved
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} mst;
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} id;
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[struct w1_netlink_cmd] - command for given master or slave device.
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__u8 cmd - command opcode.
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W1_CMD_READ - read command
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W1_CMD_WRITE - write command
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W1_CMD_SEARCH - search command
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W1_CMD_ALARM_SEARCH - alarm search command
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W1_CMD_TOUCH - touch command
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(write and sample data back to userspace)
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W1_CMD_RESET - send bus reset
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W1_CMD_SLAVE_ADD - add slave to kernel list
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W1_CMD_SLAVE_REMOVE - remove slave from kernel list
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W1_CMD_LIST_SLAVES - get slaves list from kernel
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__u8 res - reserved
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__u16 len - length of data for this command
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For read command data must be allocated like for write command
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__u8 data[0] - data for this command
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Each connector message can include one or more w1_netlink_msg with
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zero or more attached w1_netlink_cmd messages.
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For event messages there are no w1_netlink_cmd embedded structures,
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only connector header and w1_netlink_msg strucutre with "len" field
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being zero and filled type (one of event types) and id:
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either 8 bytes of slave unique id in host order,
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or master's id, which is assigned to bus master device
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when it is added to w1 core.
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Currently replies to userspace commands are only generated for read
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command request. One reply is generated exactly for one w1_netlink_cmd
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read request. Replies are not combined when sent - i.e. typical reply
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messages looks like the following::
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[cn_msg][w1_netlink_msg][w1_netlink_cmd]
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cn_msg.len = sizeof(struct w1_netlink_msg) +
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sizeof(struct w1_netlink_cmd) +
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cmd->len;
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w1_netlink_msg.len = sizeof(struct w1_netlink_cmd) + cmd->len;
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w1_netlink_cmd.len = cmd->len;
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Replies to W1_LIST_MASTERS should send a message back to the userspace
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which will contain list of all registered master ids in the following
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format::
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cn_msg (CN_W1_IDX.CN_W1_VAL as id, len is equal to sizeof(struct
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w1_netlink_msg) plus number of masters multiplied by 4)
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w1_netlink_msg (type: W1_LIST_MASTERS, len is equal to
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number of masters multiplied by 4 (u32 size))
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id0 ... idN
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Each message is at most 4k in size, so if number of master devices
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exceeds this, it will be split into several messages.
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W1 search and alarm search commands.
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request::
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[cn_msg]
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[w1_netlink_msg type = W1_MASTER_CMD
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id is equal to the bus master id to use for searching]
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[w1_netlink_cmd cmd = W1_CMD_SEARCH or W1_CMD_ALARM_SEARCH]
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reply::
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[cn_msg, ack = 1 and increasing, 0 means the last message,
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seq is equal to the request seq]
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[w1_netlink_msg type = W1_MASTER_CMD]
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[w1_netlink_cmd cmd = W1_CMD_SEARCH or W1_CMD_ALARM_SEARCH
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len is equal to number of IDs multiplied by 8]
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[64bit-id0 ... 64bit-idN]
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Length in each header corresponds to the size of the data behind it, so
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w1_netlink_cmd->len = N * 8; where N is number of IDs in this message.
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Can be zero.
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::
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w1_netlink_msg->len = sizeof(struct w1_netlink_cmd) + N * 8;
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cn_msg->len = sizeof(struct w1_netlink_msg) +
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sizeof(struct w1_netlink_cmd) +
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N*8;
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W1 reset command::
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[cn_msg]
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[w1_netlink_msg type = W1_MASTER_CMD
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id is equal to the bus master id to use for searching]
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[w1_netlink_cmd cmd = W1_CMD_RESET]
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Command status replies
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======================
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Each command (either root, master or slave with or without w1_netlink_cmd
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structure) will be 'acked' by the w1 core. Format of the reply is the same
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as request message except that length parameters do not account for data
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requested by the user, i.e. read/write/touch IO requests will not contain
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data, so w1_netlink_cmd.len will be 0, w1_netlink_msg.len will be size
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of the w1_netlink_cmd structure and cn_msg.len will be equal to the sum
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of the sizeof(struct w1_netlink_msg) and sizeof(struct w1_netlink_cmd).
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If reply is generated for master or root command (which do not have
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w1_netlink_cmd attached), reply will contain only cn_msg and w1_netlink_msg
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structures.
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w1_netlink_msg.status field will carry positive error value
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(EINVAL for example) or zero in case of success.
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All other fields in every structure will mirror the same parameters in the
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request message (except lengths as described above).
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Status reply is generated for every w1_netlink_cmd embedded in the
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w1_netlink_msg, if there are no w1_netlink_cmd structures,
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reply will be generated for the w1_netlink_msg.
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All w1_netlink_cmd command structures are handled in every w1_netlink_msg,
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even if there were errors, only length mismatch interrupts message processing.
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Operation steps in w1 core when new command is received
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=======================================================
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When new message (w1_netlink_msg) is received w1 core detects if it is
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master or slave request, according to w1_netlink_msg.type field.
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Then master or slave device is searched for.
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When found, master device (requested or those one on where slave device
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is found) is locked. If slave command is requested, then reset/select
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procedure is started to select given device.
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Then all requested in w1_netlink_msg operations are performed one by one.
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If command requires reply (like read command) it is sent on command completion.
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When all commands (w1_netlink_cmd) are processed master device is unlocked
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and next w1_netlink_msg header processing started.
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Connector [1] specific documentation
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====================================
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Each connector message includes two u32 fields as "address".
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w1 uses CN_W1_IDX and CN_W1_VAL defined in include/linux/connector.h header.
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Each message also includes sequence and acknowledge numbers.
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Sequence number for event messages is appropriate bus master sequence number
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increased with each event message sent "through" this master.
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Sequence number for userspace requests is set by userspace application.
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Sequence number for reply is the same as was in request, and
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acknowledge number is set to seq+1.
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Additional documentation, source code examples
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==============================================
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1. Documentation/driver-api/connector.rst
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2. http://www.ioremap.net/archive/w1
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This archive includes userspace application w1d.c which uses
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read/write/search commands for all master/slave devices found on the bus.
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