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linux-yocto/Documentation/i2c/ten-bit-addresses
Jean Delvare cbb4451404 i2c: Fix device name for 10-bit slave address 
10-bit addresses overlap with traditional 7-bit addresses, leading in
device name collisions. Add an arbitrary offset to 10-bit addresses to
prevent this collision. The offset was chosen so that the address is
still easily recognizable.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Wolfram Sang <w.sang@pengutronix.de>
2011-11-23 11:33:07 +01:00

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The I2C protocol knows about two kinds of device addresses: normal 7 bit addresses, and an extended set of 10 bit addresses. The sets of addresses do not intersect: the 7 bit address 0x10 is not the same as the 10 bit address 0x10 (though a single device could respond to both of them).

I2C messages to and from 10-bit address devices have a different format. See the I2C specification for the details.

The current 10 bit address support is minimal. It should work, however you can expect some problems along the way:

  • Not all bus drivers support 10-bit addresses. Some don't because the hardware doesn't support them (SMBus doesn't require 10-bit address support for example), some don't because nobody bothered adding the code (or it's there but not working properly.) Software implementation (i2c-algo-bit) is known to work.
  • Some optional features do not support 10-bit addresses. This is the case of automatic detection and instantiation of devices by their, drivers, for example.
  • Many user-space packages (for example i2c-tools) lack support for 10-bit addresses.

Note that 10-bit address devices are still pretty rare, so the limitations listed above could stay for a long time, maybe even forever if nobody needs them to be fixed.