instantiating-devices - OpenGrok cross reference for /linux-3.3/Documentation/i2c/instantiating-devices

1 How to instantiate I2C devices
4 Unlike PCI or USB devices, I2C devices are not enumerated at the hardware
6 I2C bus segment, and what address these devices are using. For this
7 reason, the kernel code must instantiate I2C devices explicitly. There are
11 Method 1: Declare the I2C devices by bus number
14 This method is appropriate when the I2C bus is a system bus as is the case
15 for many embedded systems. On such systems, each I2C bus has a number
16 which is known in advance. It is thus possible to pre-declare the I2C
45 The above code declares 3 devices on I2C bus 1, including their respective
46 addresses and custom data needed by their drivers. When the I2C bus in
47 question is registered, the I2C devices will be instantiated automatically
48 by i2c-core.
50 The devices will be automatically unbound and destroyed when the I2C bus
57 This method is appropriate when a larger device uses an I2C bus for
60 main chip by the means of an I2C bus. You won't know the number of the I2C
62 you can instantiate your I2C devices explicitly. This is done by filling
80 The above code instantiates 1 I2C device on the I2C bus which is on the
83 A variant of this is when you don't know for sure if an I2C device is
110 The above code instantiates up to 1 I2C device on the I2C bus which is on
115 The driver which instantiated the I2C device is responsible for destroying
121 Method 3: Probe an I2C bus for certain devices
124 Sometimes you do not have enough information about an I2C device, not even
133 In that case, I2C devices are neither declared nor instantiated
134 explicitly. Instead, i2c-core will probe for such devices as soon as their
135 drivers are loaded, and if any is found, an I2C device will be
138 * The I2C device driver must implement the detect() method, which
147 I2C devices instantiated as a result of such a successful probe will be
149 or when the underlying I2C bus is itself destroyed, whichever happens
152 Those of you familiar with the i2c subsystem of 2.4 kernels and early 2.6
155 * Probing is only one way to instantiate I2C devices now, while it was the
159 * I2C buses must now explicitly say which I2C driver classes can probe
160   them (by the means of the class bitfield), while all I2C buses were
173 In general, the kernel should know which I2C devices are connected and
176 interface is made of 2 attribute files which are created in every I2C bus
179 respectively delete, an I2C device.
181 File new_device takes 2 parameters: the name of the I2C device (a string)
182 and the address of the I2C device (a number, typically expressed in
185 File delete_device takes a single parameter: the address of the I2C
186 device. As no two devices can live at the same address on a given I2C
191 # echo eeprom 0x50 > /sys/bus/i2c/devices/i2c-3/new_device
195 * The I2C driver usually detects devices (method 3 above) but the bus
198 * The I2C driver usually detects devices, but your device lives at an
200 * The I2C driver usually detects devices, but your device is not detected,
203 * You are developing a driver on a test board, where you soldered the I2C
206 This interface is a replacement for the force_* module parameters some I2C
207 drivers implement. Being implemented in i2c-core rather than in each