Re: [PATCH v2] of: i2c: Add idle-disconnect DT property to PCA954x mux driver

[Alexander Sverdlin <alexander.sverdlin-OYasijW0DpE@public.gmane.org>]

Hi Wolfram!

On 15/01/15 13:32, ext Wolfram Sang wrote:
> On Fri, Dec 19, 2014 at 06:00:10PM +0100, Alexander Sverdlin wrote:
>> of: i2c: Add idle-disconnect DT property to PCA954x mux driver
>>
>> Add idle-disconnect device tree property to PCA954x mux driver. The new property
>> forces the multiplexer to disconnect child buses in idle state. This is used, for
>> example, when there are several multiplexers on the same bus and the devices on
>> the underlying buses might have same I2C addresses.
> 
> Basically OK. Question to DT maintainers: "idle-disconnect",
> "i2c-mux-idle-disconnect", or is there another existing binding we could
> use?
> 
>> At the same time old (and not used in the tree) platform data binding
>> deselect_on_exit is removed to simplify the implementation. Old binding has
>> different (per-channel) semantics and doesn't fit well in the new concept.
> 
> I'd prefer to keep it. It should be only one || more. It is not really
> in the way IMO.

It complicates the implementation 3x times :) This is part of our discussion with Laurent:
----
>>
>> I would copy pdata->modes[chan].deselect_on_exit to data->idle_disconnect
>> in the probe function, so you could avoiding accessing pdata here.
>
> Unfortunately, this pdata has different (per-channel) semantics. I cannot
> really understand, why it was done this way, but anyway it's not possible
> to use one global bit to represent per-channel bits without changing the
> behavior.
>
> I'm not keen to brake out-of-tree code (if any), but may be it will be
> decided to drop this per-channel deselect_on_exit, because it's not used at
> least in the kernel tree...

I'd vote for removing deselect_on_exit from platform data, but I won't insist.
----


-- 
Best regards,
Alexander Sverdlin.