mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-12-23 04:34:11 +08:00
e9bb627561
The 1wire documentation was written with w1 developers in mind, so, it makes sense to add it together with the driver-api set. Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
203 lines
7.1 KiB
ReStructuredText
203 lines
7.1 KiB
ReStructuredText
===============================================
|
|
Userspace communication protocol over connector
|
|
===============================================
|
|
|
|
Message types
|
|
=============
|
|
|
|
There are three types of messages between w1 core and userspace:
|
|
|
|
1. Events. They are generated each time a new master or slave device
|
|
is found either due to automatic or requested search.
|
|
2. Userspace commands.
|
|
3. Replies to userspace commands.
|
|
|
|
|
|
Protocol
|
|
========
|
|
|
|
::
|
|
|
|
[struct cn_msg] - connector header.
|
|
Its length field is equal to size of the attached data
|
|
[struct w1_netlink_msg] - w1 netlink header.
|
|
__u8 type - message type.
|
|
W1_LIST_MASTERS
|
|
list current bus masters
|
|
W1_SLAVE_ADD/W1_SLAVE_REMOVE
|
|
slave add/remove events
|
|
W1_MASTER_ADD/W1_MASTER_REMOVE
|
|
master add/remove events
|
|
W1_MASTER_CMD
|
|
userspace command for bus master
|
|
device (search/alarm search)
|
|
W1_SLAVE_CMD
|
|
userspace command for slave device
|
|
(read/write/touch)
|
|
__u8 status - error indication from kernel
|
|
__u16 len - size of data attached to this header data
|
|
union {
|
|
__u8 id[8]; - slave unique device id
|
|
struct w1_mst {
|
|
__u32 id; - master's id
|
|
__u32 res; - reserved
|
|
} mst;
|
|
} id;
|
|
|
|
[struct w1_netlink_cmd] - command for given master or slave device.
|
|
__u8 cmd - command opcode.
|
|
W1_CMD_READ - read command
|
|
W1_CMD_WRITE - write command
|
|
W1_CMD_SEARCH - search command
|
|
W1_CMD_ALARM_SEARCH - alarm search command
|
|
W1_CMD_TOUCH - touch command
|
|
(write and sample data back to userspace)
|
|
W1_CMD_RESET - send bus reset
|
|
W1_CMD_SLAVE_ADD - add slave to kernel list
|
|
W1_CMD_SLAVE_REMOVE - remove slave from kernel list
|
|
W1_CMD_LIST_SLAVES - get slaves list from kernel
|
|
__u8 res - reserved
|
|
__u16 len - length of data for this command
|
|
For read command data must be allocated like for write command
|
|
__u8 data[0] - data for this command
|
|
|
|
|
|
Each connector message can include one or more w1_netlink_msg with
|
|
zero or more attached w1_netlink_cmd messages.
|
|
|
|
For event messages there are no w1_netlink_cmd embedded structures,
|
|
only connector header and w1_netlink_msg strucutre with "len" field
|
|
being zero and filled type (one of event types) and id:
|
|
either 8 bytes of slave unique id in host order,
|
|
or master's id, which is assigned to bus master device
|
|
when it is added to w1 core.
|
|
|
|
Currently replies to userspace commands are only generated for read
|
|
command request. One reply is generated exactly for one w1_netlink_cmd
|
|
read request. Replies are not combined when sent - i.e. typical reply
|
|
messages looks like the following::
|
|
|
|
[cn_msg][w1_netlink_msg][w1_netlink_cmd]
|
|
cn_msg.len = sizeof(struct w1_netlink_msg) +
|
|
sizeof(struct w1_netlink_cmd) +
|
|
cmd->len;
|
|
w1_netlink_msg.len = sizeof(struct w1_netlink_cmd) + cmd->len;
|
|
w1_netlink_cmd.len = cmd->len;
|
|
|
|
Replies to W1_LIST_MASTERS should send a message back to the userspace
|
|
which will contain list of all registered master ids in the following
|
|
format::
|
|
|
|
cn_msg (CN_W1_IDX.CN_W1_VAL as id, len is equal to sizeof(struct
|
|
w1_netlink_msg) plus number of masters multiplied by 4)
|
|
w1_netlink_msg (type: W1_LIST_MASTERS, len is equal to
|
|
number of masters multiplied by 4 (u32 size))
|
|
id0 ... idN
|
|
|
|
Each message is at most 4k in size, so if number of master devices
|
|
exceeds this, it will be split into several messages.
|
|
|
|
W1 search and alarm search commands.
|
|
|
|
request::
|
|
|
|
[cn_msg]
|
|
[w1_netlink_msg type = W1_MASTER_CMD
|
|
id is equal to the bus master id to use for searching]
|
|
[w1_netlink_cmd cmd = W1_CMD_SEARCH or W1_CMD_ALARM_SEARCH]
|
|
|
|
reply::
|
|
|
|
[cn_msg, ack = 1 and increasing, 0 means the last message,
|
|
seq is equal to the request seq]
|
|
[w1_netlink_msg type = W1_MASTER_CMD]
|
|
[w1_netlink_cmd cmd = W1_CMD_SEARCH or W1_CMD_ALARM_SEARCH
|
|
len is equal to number of IDs multiplied by 8]
|
|
[64bit-id0 ... 64bit-idN]
|
|
|
|
Length in each header corresponds to the size of the data behind it, so
|
|
w1_netlink_cmd->len = N * 8; where N is number of IDs in this message.
|
|
Can be zero.
|
|
|
|
::
|
|
|
|
w1_netlink_msg->len = sizeof(struct w1_netlink_cmd) + N * 8;
|
|
cn_msg->len = sizeof(struct w1_netlink_msg) +
|
|
sizeof(struct w1_netlink_cmd) +
|
|
N*8;
|
|
|
|
W1 reset command::
|
|
|
|
[cn_msg]
|
|
[w1_netlink_msg type = W1_MASTER_CMD
|
|
id is equal to the bus master id to use for searching]
|
|
[w1_netlink_cmd cmd = W1_CMD_RESET]
|
|
|
|
|
|
Command status replies
|
|
======================
|
|
|
|
Each command (either root, master or slave with or without w1_netlink_cmd
|
|
structure) will be 'acked' by the w1 core. Format of the reply is the same
|
|
as request message except that length parameters do not account for data
|
|
requested by the user, i.e. read/write/touch IO requests will not contain
|
|
data, so w1_netlink_cmd.len will be 0, w1_netlink_msg.len will be size
|
|
of the w1_netlink_cmd structure and cn_msg.len will be equal to the sum
|
|
of the sizeof(struct w1_netlink_msg) and sizeof(struct w1_netlink_cmd).
|
|
If reply is generated for master or root command (which do not have
|
|
w1_netlink_cmd attached), reply will contain only cn_msg and w1_netlink_msg
|
|
structures.
|
|
|
|
w1_netlink_msg.status field will carry positive error value
|
|
(EINVAL for example) or zero in case of success.
|
|
|
|
All other fields in every structure will mirror the same parameters in the
|
|
request message (except lengths as described above).
|
|
|
|
Status reply is generated for every w1_netlink_cmd embedded in the
|
|
w1_netlink_msg, if there are no w1_netlink_cmd structures,
|
|
reply will be generated for the w1_netlink_msg.
|
|
|
|
All w1_netlink_cmd command structures are handled in every w1_netlink_msg,
|
|
even if there were errors, only length mismatch interrupts message processing.
|
|
|
|
|
|
Operation steps in w1 core when new command is received
|
|
=======================================================
|
|
|
|
When new message (w1_netlink_msg) is received w1 core detects if it is
|
|
master or slave request, according to w1_netlink_msg.type field.
|
|
Then master or slave device is searched for.
|
|
When found, master device (requested or those one on where slave device
|
|
is found) is locked. If slave command is requested, then reset/select
|
|
procedure is started to select given device.
|
|
|
|
Then all requested in w1_netlink_msg operations are performed one by one.
|
|
If command requires reply (like read command) it is sent on command completion.
|
|
|
|
When all commands (w1_netlink_cmd) are processed master device is unlocked
|
|
and next w1_netlink_msg header processing started.
|
|
|
|
|
|
Connector [1] specific documentation
|
|
====================================
|
|
|
|
Each connector message includes two u32 fields as "address".
|
|
w1 uses CN_W1_IDX and CN_W1_VAL defined in include/linux/connector.h header.
|
|
Each message also includes sequence and acknowledge numbers.
|
|
Sequence number for event messages is appropriate bus master sequence number
|
|
increased with each event message sent "through" this master.
|
|
Sequence number for userspace requests is set by userspace application.
|
|
Sequence number for reply is the same as was in request, and
|
|
acknowledge number is set to seq+1.
|
|
|
|
|
|
Additional documentation, source code examples
|
|
==============================================
|
|
|
|
1. Documentation/driver-api/connector.rst
|
|
2. http://www.ioremap.net/archive/w1
|
|
|
|
This archive includes userspace application w1d.c which uses
|
|
read/write/search commands for all master/slave devices found on the bus.
|