diff options
Diffstat (limited to 'Documentation/i2c')
| -rw-r--r-- | Documentation/i2c/instantiating-devices | 44 | ||||
| -rw-r--r-- | Documentation/i2c/writing-clients | 16 |
2 files changed, 47 insertions, 13 deletions
diff --git a/Documentation/i2c/instantiating-devices b/Documentation/i2c/instantiating-devices index b55ce57a84d..c740b7b4108 100644 --- a/Documentation/i2c/instantiating-devices +++ b/Documentation/i2c/instantiating-devices @@ -165,3 +165,47 @@ was done there. Two significant differences are: Once again, method 3 should be avoided wherever possible. Explicit device instantiation (methods 1 and 2) is much preferred for it is safer and faster. + + +Method 4: Instantiate from user-space +------------------------------------- + +In general, the kernel should know which I2C devices are connected and +what addresses they live at. However, in certain cases, it does not, so a +sysfs interface was added to let the user provide the information. This +interface is made of 2 attribute files which are created in every I2C bus +directory: new_device and delete_device. Both files are write only and you +must write the right parameters to them in order to properly instantiate, +respectively delete, an I2C device. + +File new_device takes 2 parameters: the name of the I2C device (a string) +and the address of the I2C device (a number, typically expressed in +hexadecimal starting with 0x, but can also be expressed in decimal.) + +File delete_device takes a single parameter: the address of the I2C +device. As no two devices can live at the same address on a given I2C +segment, the address is sufficient to uniquely identify the device to be +deleted. + +Example: +# echo eeprom 0x50 > /sys/class/i2c-adapter/i2c-3/new_device + +While this interface should only be used when in-kernel device declaration +can't be done, there is a variety of cases where it can be helpful: +* The I2C driver usually detects devices (method 3 above) but the bus + segment your device lives on doesn't have the proper class bit set and + thus detection doesn't trigger. +* The I2C driver usually detects devices, but your device lives at an + unexpected address. +* The I2C driver usually detects devices, but your device is not detected, + either because the detection routine is too strict, or because your + device is not officially supported yet but you know it is compatible. +* You are developing a driver on a test board, where you soldered the I2C + device yourself. + +This interface is a replacement for the force_* module parameters some I2C +drivers implement. Being implemented in i2c-core rather than in each +device driver individually, it is much more efficient, and also has the +advantage that you do not have to reload the driver to change a setting. +You can also instantiate the device before the driver is loaded or even +available, and you don't need to know what driver the device needs. diff --git a/Documentation/i2c/writing-clients b/Documentation/i2c/writing-clients index c1a06f989cf..7860aafb483 100644 --- a/Documentation/i2c/writing-clients +++ b/Documentation/i2c/writing-clients @@ -126,19 +126,9 @@ different) configuration information, as do drivers handling chip variants that can't be distinguished by protocol probing, or which need some board specific information to operate correctly. -Accordingly, the I2C stack now has two models for associating I2C devices -with their drivers: the original "legacy" model, and a newer one that's -fully compatible with the Linux 2.6 driver model. These models do not mix, -since the "legacy" model requires drivers to create "i2c_client" device -objects after SMBus style probing, while the Linux driver model expects -drivers to be given such device objects in their probe() routines. -The legacy model is deprecated now and will soon be removed, so we no -longer document it here. - - -Standard Driver Model Binding ("New Style") -------------------------------------------- +Device/Driver Binding +--------------------- System infrastructure, typically board-specific initialization code or boot firmware, reports what I2C devices exist. For example, there may be @@ -201,7 +191,7 @@ a given I2C bus. This is for example the case of hardware monitoring devices on a PC's SMBus. In that case, you may want to let your driver detect supported devices automatically. This is how the legacy model was working, and is now available as an extension to the standard -driver model (so that we can finally get rid of the legacy model.) +driver model. You simply have to define a detect callback which will attempt to identify supported devices (returning 0 for supported ones and -ENODEV |