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Jean Delvarec7b25a92009-12-06 17:06:24 +01001I2C device driver binding control from user-space
2=================================================
3
4Up to kernel 2.6.32, many i2c drivers used helper macros provided by
5<linux/i2c.h> which created standard module parameters to let the user
6control how the driver would probe i2c buses and attach to devices. These
7parameters were known as "probe" (to let the driver probe for an extra
8address), "force" (to forcibly attach the driver to a given device) and
9"ignore" (to prevent a driver from probing a given address).
10
11With the conversion of the i2c subsystem to the standard device driver
12binding model, it became clear that these per-module parameters were no
13longer needed, and that a centralized implementation was possible. The new,
14sysfs-based interface is described in the documentation file
15"instantiating-devices", section "Method 4: Instantiate from user-space".
16
17Below is a mapping from the old module parameters to the new interface.
18
19Attaching a driver to an I2C device
20-----------------------------------
21
22Old method (module parameters):
23# modprobe <driver> probe=1,0x2d
24# modprobe <driver> force=1,0x2d
25# modprobe <driver> force_<device>=1,0x2d
26
27New method (sysfs interface):
28# echo <device> 0x2d > /sys/bus/i2c/devices/i2c-1/new_device
29
30Preventing a driver from attaching to an I2C device
31---------------------------------------------------
32
33Old method (module parameters):
34# modprobe <driver> ignore=1,0x2f
35
36New method (sysfs interface):
37# echo dummy 0x2f > /sys/bus/i2c/devices/i2c-1/new_device
38# modprobe <driver>
39
40Of course, it is important to instantiate the "dummy" device before loading
41the driver. The dummy device will be handled by i2c-core itself, preventing
42other drivers from binding to it later on. If there is a real device at the
43problematic address, and you want another driver to bind to it, then simply
44pass the name of the device in question instead of "dummy".