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authorLinus Torvalds <torvalds@linux-foundation.org>2009-12-08 19:12:16 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2009-12-08 19:12:16 +0300
commit41440ffe21f29bdb985cab76b2d0b06d83e63b19 (patch)
tree1d7d1ff6f699ccbabb71c7bc4172f7d15bc4bc45 /Documentation/i2c/old-module-parameters
parentdad3de7d0090280f44ff27131ed2878f1ab6ddad (diff)
parent6471b68982d3bb1a593c3e183c804ecf830125d3 (diff)
downloadlinux-41440ffe21f29bdb985cab76b2d0b06d83e63b19.tar.xz
Merge branch 'i2c-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jdelvare/staging
* 'i2c-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jdelvare/staging: i2c-stub: Documentation update i2c-stub: Allow user to disable some commands i2c-stub: Implement I2C block support i2c: Refactor for_each callbacks i2c-i801: Retry on lost arbitration i2c: Remove big kernel lock from i2cdev_open ics932s401: Clean up detect function i2c: Simplify i2c_detect_address i2c: Drop probe, ignore and force module parameters i2c: Add missing __devinit markers to old i2c adapter drivers i2c: Bus drivers don't have to support I2C_M_REV_DIR_ADDR i2c: Prevent priority inversion on top of bus lock i2c-voodoo3: Delete i2c-powermac: Drop temporary name buffer i2c-powermac: Include the i2c_adapter in struct pmac_i2c_bus i2c-powermac: Log errors i2c-powermac: Refactor i2c_powermac_smbus_xfer i2c-powermac: Reject unsupported I2C transactions i2c/chips: Move ds1682 to drivers/misc
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+I2C device driver binding control from user-space
+=================================================
+
+Up to kernel 2.6.32, many i2c drivers used helper macros provided by
+<linux/i2c.h> which created standard module parameters to let the user
+control how the driver would probe i2c buses and attach to devices. These
+parameters were known as "probe" (to let the driver probe for an extra
+address), "force" (to forcibly attach the driver to a given device) and
+"ignore" (to prevent a driver from probing a given address).
+
+With the conversion of the i2c subsystem to the standard device driver
+binding model, it became clear that these per-module parameters were no
+longer needed, and that a centralized implementation was possible. The new,
+sysfs-based interface is described in the documentation file
+"instantiating-devices", section "Method 4: Instantiate from user-space".
+
+Below is a mapping from the old module parameters to the new interface.
+
+Attaching a driver to an I2C device
+-----------------------------------
+
+Old method (module parameters):
+# modprobe <driver> probe=1,0x2d
+# modprobe <driver> force=1,0x2d
+# modprobe <driver> force_<device>=1,0x2d
+
+New method (sysfs interface):
+# echo <device> 0x2d > /sys/bus/i2c/devices/i2c-1/new_device
+
+Preventing a driver from attaching to an I2C device
+---------------------------------------------------
+
+Old method (module parameters):
+# modprobe <driver> ignore=1,0x2f
+
+New method (sysfs interface):
+# echo dummy 0x2f > /sys/bus/i2c/devices/i2c-1/new_device
+# modprobe <driver>
+
+Of course, it is important to instantiate the "dummy" device before loading
+the driver. The dummy device will be handled by i2c-core itself, preventing
+other drivers from binding to it later on. If there is a real device at the
+problematic address, and you want another driver to bind to it, then simply
+pass the name of the device in question instead of "dummy".