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. Includes read/write and search/alarm search comamnds. 3. Replies to userspace commands. From: Evgeniy Polyakov <johnpol@2ka.mipt.ru> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>tirimbino
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Userspace communication protocol over connector [1]. |
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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 new master or slave device found |
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either due to automatic or requested search. |
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2. Userspace commands. Includes read/write and search/alarm search comamnds. |
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3. Replies to userspace commands. |
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Protocol. |
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======== |
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[struct cn_msg] - connector header. It's 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_SLAVE_ADD/W1_SLAVE_REMOVE - slave add/remove events. |
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W1_MASTER_ADD/W1_MASTER_REMOVE - master add/remove events. |
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W1_MASTER_CMD - userspace command for bus master device (search/alarm search). |
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W1_SLAVE_CMD - userspace command for slave device (read/write/ search/alarm search |
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for bus master device where given slave device found). |
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__u8 res - reserved |
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__u16 len - size of attached to this header data. |
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union { |
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__u8 id; - 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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[strucrt w1_netlink_cmd] - command for gived 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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__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 zero of more attached w1_netlink_cmd messages. |
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For event messages there are no w1_netlink_cmd embedded structures, only connector header |
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and w1_netlink_msg strucutre with "len" field being zero and filled type (one of event types) |
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and id - either 8 bytes of slave unique id in host order, or master's id, which is assigned |
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to bus master device when it is added to w1 core. |
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Currently replies to userspace commands are only generated for read command request. |
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One reply is generated exactly for one w1_netlink_cmd read request. |
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Replies are not combined when sent - i.e. typical reply 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) + sizeof(struct w1_netlink_cmd) + 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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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 master of slave request, |
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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 is found) is locked. |
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If slave command is requested, then reset/select 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 muster 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 increased with |
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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 documantion, source code examples. |
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============================================ |
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1. Documentation/connector |
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2. http://tservice.net.ru/~s0mbre/archive/w1 |
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This archive includes userspace application w1d.c which |
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uses read/write/search commands for all master/slave devices found on the bus. |
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