Re: Another problem with I2C multiplexer bus naming - solved

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

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On Thu, Mar 12, 2015 at 11:49:48AM -0700, Bob Feretich wrote:
> On 3/12/2015 2:44 AM, Wolfram Sang wrote:
> >On Wed, Mar 11, 2015 at 09:55:51PM -0700, Bob Feretich wrote:
> >
> >>I tried some random things and setting aliases in the dtsi file solved
> >>the problem.
> >
> >Good.
> >
> >>The use of an alias to set the name of an i2c bus should
> >>be documented somewhere!
> >
> >Well, send a patch adding some documentation where you would have liked
> >to see it.
> >
> >Thanks,
> >
> >    Wolfram
> >
> The first two places I looked for information were:
> *
> https://www.kernel.org/doc/Documentation/devicetree/bindings/i2c/i2c-mux.txt
> 
>   This is where I found the info on specifying the multiplexer without
>   aliases. It would seem logical to add the description of "how to
>   explicitly name child buses" here.

Please do. You know best what kind of information you'd like to see
there.

> * https://www.kernel.org/doc/Documentation/i2c/muxes/i2c-mux-gpio
>   Even though this file is for gpio controlled multiplexers, it seemed
>   like a good spot to look for information on how to specify i2c
>   multiplexers in general. It only describes the board.c method of
>   registering adapters. (I don't know which  gpio_i2cmux_platform_data
>   fields would be the equivalent of specifying the device tree aliases.)
>   Perhaps a cross-reference to the above documentation is appropriate,
>   since use of customized board.c files is being discouraged.

Send a patch and we will see :)

> Note that once device trees become dynamic and support hot plugging, the
> alias bus naming solution becomes ineffective, unless there is a way to
> specify a hierarchical alias that references the bus/adapter id of the
> multiplexer.

I2C was never considered hot-pluggable in the days. So, anyone wanting to
use it this way needs to spend some effort adding it. Some steps have
already been taken, though (e.g. dynamic of reconfig).


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