On 10/31/2014 02:03 PM, Wolfram Sang wrote:
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 didn't follow up on the issue since it was not an immediate concern,
and my proposed solution had some problems. If I remember correctly,
one of the problems was that the multiplexer does not have to be an
i2c chip. In that case XX would be unknown and/or have to be omitted.
Guenter
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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