[PATCH] w1: Updates the w1 documentation (w1.generic)

Any w1 device must be connected to w1 bus master device - for example

ds9490 usb device or w1-over-GPIO or RS232 converter.

Driver for w1 bus master must provide several functions(you can find

them in struct w1_bus_master definition in w1.h) which then will be

called by w1 core to send various commands over w1 bus(by default it is

reset and search commands). When some device is found on the bus, w1 core

checks if driver for it's family is loaded.

If driver is loaded w1 core creates new w1_slave object and registers it

in the system(creates some generic sysfs files(struct w1_family_ops in

w1_family.h), notifies any registered listener and so on...).

It is device driver's business to provide any communication method

upstream.

For example w1_therm driver(ds18?20 thermal sensor family driver)

The 1-wire (w1) subsystem

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The 1-wire bus is a simple master-slave bus that communicates via a single

signal wire (plus ground, so two wires).

Devices communicate on the bus by pulling the signal to ground via an open

drain output and by sampling the logic level of the signal line.

The w1 subsystem provides the framework for managing w1 masters and

communication with slaves.

All w1 slave devices must be connected to a w1 bus master device.

Example w1 master devices:

    DS9490 usb device

    W1-over-GPIO

    DS2482 (i2c to w1 bridge)

    Emulated devices, such as a RS232 converter, parallel port adapter, etc

What does the w1 subsystem do?

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When a w1 master driver registers with the w1 subsystem, the following occurs:

 - sysfs entries for that w1 master are created

 - the w1 bus is periodically searched for new slave devices

When a device is found on the bus, w1 core checks if driver for it's family is

loaded. If so, the family driver is attached to the slave.

If there is no driver for the family, a simple sysfs entry is created

for the slave device.

W1 device families

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Slave devices are handled by a driver written for a family of w1 devices.

A family driver populates a struct w1_family_ops (see w1_family.h) and

registers with the w1 subsystem.

Current family drivers:

w1_therm - (ds18?20 thermal sensor family driver)

    provides temperature reading function which is bound to ->rbin() method

    of the above w1_family_ops structure.

w1_smem - driver for simple 64bit memory cell provides ID reading

method.

w1_smem - driver for simple 64bit memory cell provides ID reading method.

You can call above methods by reading appropriate sysfs files.

What does a w1 master driver need to implement?

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The driver for w1 bus master must provide at minimum two functions.

Emulated devices must provide the ability to set the output signal level

(write_bit) and sample the signal level (read_bit).

Devices that support the 1-wire natively must provide the ability to write and

sample a bit (touch_bit) and reset the bus (reset_bus).

Most hardware provides higher-level functions that offload w1 handling.

See struct w1_bus_master definition in w1.h for details.

w1 master sysfs interface

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<xx-xxxxxxxxxxxxx> - a directory for a found device. The format is family-serial

bus                - (standard) symlink to the w1 bus

driver             - (standard) symlink to the w1 driver

w1_master_attempts - the number of times a search was attempted

w1_master_max_slave_count

                   - the maximum slaves that may be attached to a master

w1_master_name     - the name of the device (w1_bus_masterX)

w1_master_search   - the number of searches left to do, -1=continual (default)

w1_master_slave_count

                   - the number of slaves found

w1_master_slaves   - the names of the slaves, one per line

w1_master_timeout  - the delay in seconds between searches

If you have a w1 bus that never changes (you don't add or remove devices),

you can set w1_master_search to a positive value to disable searches.

w1 slave sysfs interface

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bus                - (standard) symlink to the w1 bus

driver             - (standard) symlink to the w1 driver

name               - the device name, usually the same as the directory name

w1_slave           - (optional) a binary file whose meaning depends on the

                     family driver