forked from Minki/linux
cfa0327b0d
We now have seperate address spaces for 10 bit and we-are-slave clients. Update the sysfs device instantiation method to support these types by accepting the address offsets that are assigned to the extra address spaces. Update the documentation, too. Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
29 lines
1.5 KiB
Plaintext
29 lines
1.5 KiB
Plaintext
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).
|
|
To avoid ambiguity, the user sees 10 bit addresses mapped to a different
|
|
address space, namely 0xa000-0xa3ff. The leading 0xa (= 10) represents the
|
|
10 bit mode. This is used for creating device names in sysfs. It is also
|
|
needed when instantiating 10 bit devices via the new_device file in sysfs.
|
|
|
|
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.
|