[lm-sensors] [PATCH 2.6] I2C: Rewrite i2c_probe

[khali@linux-fr.org (Jean Delvare)]

Hi David,

> From places like below (a snippet from your patch). You use 0 instead
> of preprocessor tokens. It is also this way in various other places
> in the i2c core code.
> 
> // Snippet of i2c_probe_addresses
> +	/* Make sure there is something at this address, unless forced */
> +	if (kind < 0
> +	 && i2c_smbus_xfer(adapter, addr, 0, 0, 0, I2C_SMBUS_QUICK, NULL) < 0)
> +		return 0;
> // Snippet end

As far as I can see only one "0" (the middle one) has a replacement
preprocessor token (I2C_SMBUS_WRITE), right? I don't think we have
preprocessor token for "no flags" nor "command doesn't matter", and I
don't think we should introduce them, as 0 is just as natural in this
case.

I think that I2C_SMBUS_WRITE is not used here on purpose, because there
is not such thing as a quick read command in the SMBus protocol. The
quick command is always a write, sending a single bit of data to the
target chip. This is a *very* weird choice from Intel if you want my
opinion, but that's the way SMBus was designed. I'd expect that you will
find 0 or 1 instead of I2C_SMBUS_WRITE or I2C_SMBUS_READ, respectively,
only when I2C_SMBUS_QUICK is used. If this is the case, that's not
something we want to change, as it makes some sense with regards to the
SMBus protocol.

Now, if there are non-quick commands not using I2C_SMBUS_WRITE/READ when
they should, please point them out to us.

Thanks,
-- 
Jean Delvare