[PATCH 3/4] devicetree: bindings: Add defeature-repeated-start property for Cadence I2C

Lars-Peter Clausen lars at metafoo.de
Tue Dec 2 07:12:48 PST 2014

On 12/02/2014 03:15 PM, Wolfram Sang wrote:
>>> What do you do when disable repeated start? Sending STOP and START? If
>>> so, this is really something different than repeated start. By using
>>> I2C_FUNC_I2C a user expects repeated start, so if the HW does not
>>> support it, we should say so and don't try to emulate it with something
>>> different.
>> Yes, we send stop.
> As said before, this is wrong. Another master could interfere between
> the messages when using stop+start. This is no replacement for repeated
> start.

More importantly a lot of I2C slaves also reset their internal state machine 
on a stop. So e.g. if reading a register is implemented by doing 
start,write,repeated start,read,stop and you replace that with 
start,write,stop,start,read,stop you'll always read register zero instead of 
the register you wanted to read.

- Lars

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