Re: Problem with multiple i2c multiplexers on the same bus

[Wolfram Sang <wsa-z923LK4zBo2bacvFa/9K2g@public.gmane.org>]

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Hi,

On Mon, Oct 27, 2014 at 11:46:01AM -0700, Martin Belanger wrote:
> This is regarding a series of emails between Guenter Roeck and Jean
> Delvare titled "Problem with multiple i2c multiplexers on one bus, and
> mux bus naming" sent in November 2013. Ref:
> http://thread.gmane.org/gmane.linux.drivers.i2c/16980

Please CC those people then, too. That helps getting their attention.
I've done this now.

> I'm having the same problem with multiple PCA954x multiplexers on the
> same bus and there is no way to tell them apart just by looking at the
> "name" file.
> 
> There was a suggestion to change the name from "i2c-N-mux (chan_id M)"
> to "i2c-N-mux-XX (chan_id M)" or even "i2c-N-mux-i2c-XX (chan_id M)",
> where XX is the multiplexer's i2c address. That would solve my
> problem, but unfortunately it looks like Guenter never submitted the
> patch (or maybe it was rejected?).

It just dropped off :( But you guys have my attention now, let's fix
this issue for 3.19! I am just reading through the old mails and will
think about it. Input is welcome.

> I would like to submit a similar change, but I was thinking of adding
> a module parameter so that the change is not the default behavior.
> The idea is to preserve backward compatibility for applications that
> don't require this fix. For example, modprobe i2c-dev
> explicit_mux_id=1 would use i2c-N-mux-i2c-XX (chan_id M), whereas
> modprobe i2c-dev would default to the current behavior: i.e. i2c-N-mux
> (chan_id M).

I don't like the need to set a module parameter to fix a flaw. I do
consider changing the ABI to have better strings in "name". But as said,
I need to think about it a little more...

Thanks,

   Wolfram


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