summaryrefslogtreecommitdiffstats
path: root/kernel/Documentation/i2c/ten-bit-addresses
diff options
context:
space:
mode:
Diffstat (limited to 'kernel/Documentation/i2c/ten-bit-addresses')
-rw-r--r--kernel/Documentation/i2c/ten-bit-addresses24
1 files changed, 24 insertions, 0 deletions
diff --git a/kernel/Documentation/i2c/ten-bit-addresses b/kernel/Documentation/i2c/ten-bit-addresses
new file mode 100644
index 000000000..cdfe13901
--- /dev/null
+++ b/kernel/Documentation/i2c/ten-bit-addresses
@@ -0,0 +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).
+
+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.