Based on kernel version 4.15. Page generated on 2018-01-29 10:00 EST.
1 The I2C protocol knows about two kinds of device addresses: normal 7 bit 2 addresses, and an extended set of 10 bit addresses. The sets of addresses 3 do not intersect: the 7 bit address 0x10 is not the same as the 10 bit 4 address 0x10 (though a single device could respond to both of them). 5 To avoid ambiguity, the user sees 10 bit addresses mapped to a different 6 address space, namely 0xa000-0xa3ff. The leading 0xa (= 10) represents the 7 10 bit mode. This is used for creating device names in sysfs. It is also 8 needed when instantiating 10 bit devices via the new_device file in sysfs. 9 10 I2C messages to and from 10-bit address devices have a different format. 11 See the I2C specification for the details. 12 13 The current 10 bit address support is minimal. It should work, however 14 you can expect some problems along the way: 15 * Not all bus drivers support 10-bit addresses. Some don't because the 16 hardware doesn't support them (SMBus doesn't require 10-bit address 17 support for example), some don't because nobody bothered adding the 18 code (or it's there but not working properly.) Software implementation 19 (i2c-algo-bit) is known to work. 20 * Some optional features do not support 10-bit addresses. This is the 21 case of automatic detection and instantiation of devices by their, 22 drivers, for example. 23 * Many user-space packages (for example i2c-tools) lack support for 24 10-bit addresses. 25 26 Note that 10-bit address devices are still pretty rare, so the limitations 27 listed above could stay for a long time, maybe even forever if nobody 28 needs them to be fixed.