Re: [RFC 0/5] Add I3C subsystem

Wolfram Sang
2017-07-31T19:17:49Z

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Hi Boris,

> This patch series is a proposal for a new I3C [1] subsystem.

Nice. Good luck with that!

Some hi-level comments from me related to I2C. I can't say a lot more
because the specs are not public :(

> - the bus element is a separate object and is not implicitly described
> by the master (as done in I2C). The reason is that I want to be able
> to handle multiple master connected to the same bus and visible to
> Linux.
> In this situation, we should only have one instance of the device and
> not one per master, and sharing the bus object would be part of the
> solution to gracefully handle this case.
> I'm not sure if we will ever need to deal with multiple masters
> controlling the same bus and exposed under Linux, but separating the
> bus and master concept is pretty easy, hence the decision to do it
> now, just in case we need it some day.

From my experience, it is a good thing to have this separation.

> - I2C backward compatibility has been designed to be transparent to I2C
> drivers and the I2C subsystem. The I3C master just registers an I2C
> adapter which creates a new I2C bus. I'd say that, from a
> representation PoV it's not ideal because what should appear as a
> single I3C bus exposing I3C and I2C devices here appears as 2
> different busses connected to each other through the parenting (the
> I3C master is the parent of the I2C and I3C busses).
> On the other hand, I don't see a better solution if we want something
> that is not invasive.

I agree this is the least invasive and also the most compatible
approach. The other solution would probably be to have some kind of
emulation layer?

> I'd also like to get feedback on the doc. Should I detail a bit more
> the protocol or the framework API? Is this the kind of things you
> expect in a subsystem doc?

Since the spec is not public, details about the protocol will be
especially useful, I'd say.

Regards,

Wolfram

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