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authorMark Brown <broonie@opensource.wolfsonmicro.com>2012-05-30 10:55:34 +0200
committerJean Delvare <khali@endymion.delvare>2012-05-30 10:55:34 +0200
commit14674e70119ea01549ce593d8901a797f8a90f74 (patch)
tree15474236bfa505aa396bf2892cbbee65e842b94b /Documentation/i2c
parent838bfa6049fb84dc66c9c9bbeb3a968ec987fd3d (diff)
downloadlinux-linaro-stable-14674e70119ea01549ce593d8901a797f8a90f74.tar.gz
i2c: Split I2C_M_NOSTART support out of I2C_FUNC_PROTOCOL_MANGLING
Since there are uses for I2C_M_NOSTART which are much more sensible and standard than most of the protocol mangling functionality (the main one being gather writes to devices where something like a register address needs to be inserted before a block of data) create a new I2C_FUNC_NOSTART for this feature and update all the users to use it. Also strengthen the disrecommendation of the protocol mangling while we're at it. In the case of regmap-i2c we remove the requirement for mangling as I2C_M_NOSTART is the only mangling feature which is being used. Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com> Acked-by: Wolfram Sang <w.sang@pengutronix.de> Signed-off-by: Jean Delvare <khali@linux-fr.org>
Diffstat (limited to 'Documentation/i2c')
-rw-r--r--Documentation/i2c/functionality9
-rw-r--r--Documentation/i2c/i2c-protocol9
2 files changed, 14 insertions, 4 deletions
diff --git a/Documentation/i2c/functionality b/Documentation/i2c/functionality
index 42c17c1fb3cd..b0ff2ab596ce 100644
--- a/Documentation/i2c/functionality
+++ b/Documentation/i2c/functionality
@@ -18,9 +18,9 @@ For the most up-to-date list of functionality constants, please check
adapters typically can not do these)
I2C_FUNC_10BIT_ADDR Handles the 10-bit address extensions
I2C_FUNC_PROTOCOL_MANGLING Knows about the I2C_M_IGNORE_NAK,
- I2C_M_REV_DIR_ADDR, I2C_M_NOSTART and
- I2C_M_NO_RD_ACK flags (which modify the
- I2C protocol!)
+ I2C_M_REV_DIR_ADDR and I2C_M_NO_RD_ACK
+ flags (which modify the I2C protocol!)
+ I2C_FUNC_NOSTART Can skip repeated start sequence
I2C_FUNC_SMBUS_QUICK Handles the SMBus write_quick command
I2C_FUNC_SMBUS_READ_BYTE Handles the SMBus read_byte command
I2C_FUNC_SMBUS_WRITE_BYTE Handles the SMBus write_byte command
@@ -50,6 +50,9 @@ A few combinations of the above flags are also defined for your convenience:
emulated by a real I2C adapter (using
the transparent emulation layer)
+In kernel versions prior to 3.5 I2C_FUNC_NOSTART was implemented as
+part of I2C_FUNC_PROTOCOL_MANGLING.
+
ADAPTER IMPLEMENTATION
----------------------
diff --git a/Documentation/i2c/i2c-protocol b/Documentation/i2c/i2c-protocol
index 10518dd58814..0b3e62d1f77a 100644
--- a/Documentation/i2c/i2c-protocol
+++ b/Documentation/i2c/i2c-protocol
@@ -49,7 +49,9 @@ a byte read, followed by a byte write:
Modified transactions
=====================
-We have found some I2C devices that needs the following modifications:
+The following modifications to the I2C protocol can also be generated,
+with the exception of I2C_M_NOSTART these are usually only needed to
+work around device issues:
Flag I2C_M_NOSTART:
In a combined transaction, no 'S Addr Wr/Rd [A]' is generated at some
@@ -60,6 +62,11 @@ We have found some I2C devices that needs the following modifications:
we do not generate Addr, but we do generate the startbit S. This will
probably confuse all other clients on your bus, so don't try this.
+ This is often used to gather transmits from multiple data buffers in
+ system memory into something that appears as a single transfer to the
+ I2C device but may also be used between direction changes by some
+ rare devices.
+
Flags I2C_M_REV_DIR_ADDR
This toggles the Rd/Wr flag. That is, if you want to do a write, but
need to emit an Rd instead of a Wr, or vice versa, you set this