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author | Jean Delvare <khali@linux-fr.org> | 2011-11-23 11:33:07 +0100 |
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committer | Jean Delvare <khali@endymion.delvare> | 2011-11-23 11:33:07 +0100 |
commit | cbb44514048a250647c6c6b3df27ff62cb71f7d5 (patch) | |
tree | 47b64df0a06edd7f7eca94d2f9f8d08f070b1ef5 /Documentation/i2c/ten-bit-addresses | |
parent | cc6bcf7d2ec2234e7b41770185e4dc826390185e (diff) | |
download | linux-cbb44514048a250647c6c6b3df27ff62cb71f7d5.tar.gz linux-cbb44514048a250647c6c6b3df27ff62cb71f7d5.tar.bz2 linux-cbb44514048a250647c6c6b3df27ff62cb71f7d5.zip |
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>
Diffstat (limited to 'Documentation/i2c/ten-bit-addresses')
-rw-r--r-- | Documentation/i2c/ten-bit-addresses | 36 |
1 files changed, 19 insertions, 17 deletions
diff --git a/Documentation/i2c/ten-bit-addresses b/Documentation/i2c/ten-bit-addresses index e9890709c508..cdfe13901b99 100644 --- a/Documentation/i2c/ten-bit-addresses +++ b/Documentation/i2c/ten-bit-addresses @@ -1,22 +1,24 @@ 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). You -select a 10 bit address by adding an extra byte after the address -byte: - S Addr7 Rd/Wr .... -becomes - S 11110 Addr10 Rd/Wr -S is the start bit, Rd/Wr the read/write bit, and if you count the number -of bits, you will see the there are 8 after the S bit for 7 bit addresses, -and 16 after the S bit for 10 bit addresses. +address 0x10 (though a single device could respond to both of them). -WARNING! The current 10 bit address support is EXPERIMENTAL. There are -several places in the code that will cause SEVERE PROBLEMS with 10 bit -addresses, even though there is some basic handling and hooks. Also, -almost no supported adapter handles the 10 bit addresses correctly. +I2C messages to and from 10-bit address devices have a different format. +See the I2C specification for the details. -As soon as a real 10 bit address device is spotted 'in the wild', we -can and will add proper support. Right now, 10 bit address devices -are defined by the I2C protocol, but we have never seen a single device -which supports them. +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. |