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

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

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On Thu, Jan 15, 2015 at 02:09:09PM +0100, Alexander Sverdlin wrote:
> 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:

Does it? I don't want DT and platform_data to behave equally. I just
want to keep being backwards compatible. So, I'd suggest:

(pdata && pdata->modes[num].deselect_on_exit) || idle_disconnect ? pca954x_deselect_mux : NULL);

> > 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 couldn't find a user of the platform_data, at all. But removing
platform_data support is a seperate patch, and deprecating platform_data
is a seperate and general issue IMO.


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