i2c/ smbus question

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

Hi !

Can you confirm the difference between writing a block of data with
I2C_SMBUS_BLOCK_DATA vs I2C_SMBUS_I2C_BLOCK_DATA on the wire ? It's my
understanding that the former will actually send the lenght byte on the
wire before the data while the later won't, though they both send a
subaddress.

I'm completely rewriting the powermac i2c support (consolidating all
busses behind a low level layer that I need to use in circumstances
where the linux i2c layer isn't useable, and with a single driver in
drivers/i2c/busses/* replacing i2c-keywest.c and i2c-pmac-smu.c) and I
think I'm hitting a problem where i2c-keywest didn't implement
I2C_SMBUS_BLOCK_DATA properly (didn't send the lenght byte) and some
drivers (our sound drivers) rely on that behaviour (that's fine, I can
fix them too, I just want to make sure I understand what the semantic
should be).

I'm a bit surprised that there seem to be no wrapper for writing with
I2C_SMBUS_I2C_BLOCK_DATA, only for reading, in i2c-core.c since it
appears to me that it's the most common one, at least for all devices
I've dealt with so far (mostly sound & clock chips in addition to
sensors)...

Cheers,
Ben.