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

From: Lars-Peter Clausen
Date: Tue Dec 02 2014 - 10:12:59 EST

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

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

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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