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author | James Morris <jmorris@namei.org> | 2009-06-30 09:10:35 +1000 |
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committer | James Morris <jmorris@namei.org> | 2009-06-30 09:10:35 +1000 |
commit | ac7242142b03421c96b0a2f8d99f146d075614c2 (patch) | |
tree | b0b2ead65858c7a343d38affed86fe815e37e7e9 /Documentation/i2c/instantiating-devices | |
parent | 89c86576ecde504da1eeb4f4882b2189ac2f9c4a (diff) | |
parent | 2bfdd79eaa0043346e773ba5f6cfd811ea31b73d (diff) | |
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Merge branch 'master' into next
Diffstat (limited to 'Documentation/i2c/instantiating-devices')
-rw-r--r-- | Documentation/i2c/instantiating-devices | 44 |
1 files changed, 44 insertions, 0 deletions
diff --git a/Documentation/i2c/instantiating-devices b/Documentation/i2c/instantiating-devices index b55ce57a84db..c740b7b41088 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. |