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@xxxxxxxxxxxx> Acked-by: Wolfram Sang <w.sang@xxxxxxxxxxxxxx> --- Documentation/i2c/ten-bit-addresses | 36 ++++++++++++++++++----------------- drivers/i2c/i2c-core.c | 4 ++- 2 files changed, 22 insertions(+), 18 deletions(-) --- linux-3.2-rc2.orig/drivers/i2c/i2c-core.c 2011-11-16 11:13:50.000000000 +0100 +++ linux-3.2-rc2/drivers/i2c/i2c-core.c 2011-11-16 15:56:55.000000000 +0100 @@ -539,8 +539,10 @@ i2c_new_device(struct i2c_adapter *adap, client->dev.type = &i2c_client_type; client->dev.of_node = info->of_node; + /* For 10-bit clients, add an arbitrary offset to avoid collisions */ dev_set_name(&client->dev, "%d-%04x", i2c_adapter_id(adap), - client->addr); + client->addr | ((client->flags & I2C_CLIENT_TEN) + ? 0xa000 : 0)); status = device_register(&client->dev); if (status) goto out_err; --- linux-3.2-rc2.orig/Documentation/i2c/ten-bit-addresses 2011-11-16 11:13:50.000000000 +0100 +++ linux-3.2-rc2/Documentation/i2c/ten-bit-addresses 2011-11-16 11:14:33.000000000 +0100 @@ -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. -- Jean Delvare -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
