Re: [PATCH v3 1/4] i2c: mux-pinctrl: Rework to honor disabled child nodes

From: Sebastian Hesselbarth
Date: Wed Mar 18 2015 - 19:10:41 EST

On 18.03.2015 15:00, Wolfram Sang wrote:
On Wed, Mar 18, 2015 at 02:23:18PM +0100, Sebastian Hesselbarth wrote:
Possible. But this change just makes i2c-mux-pinctrl honor status
property at all. There is no functional change except it now allows
you to disable any of the sub-busses.

Actually, this is the feature I like. However, I wonder if we shouldn't
have that in the core, say in of_i2c_register_devices()?

Hmm, looking at of_i2c_register_devices():

for_each_available_child_of_node(adap->dev.of_node, node)
of_i2c_register_device(adap, node);

already honors status properties by using for_each_available_foo.
Therefore, i2c-core will also skip i2c device nodes disabled by
status property.

I agree that this driver still does not cope well with DYNAMIC_OF but
neither did the former implementation. How about we settle this driver
to this implementation now and wait for any maniac that wants to use it
the way you are suggesting above?

Sure. I don't want you to make this driver OF_DYNAMIC compatible. I just
thought it makes it harder, though, e.g. you allocate memory for the
number of active busses not the number of possibilities, so that would
have to be reverted by the "maniac". I am still at the glimpse level,
but what if we let the mux-pinctrl parse all the data (even for disabled
busses), but only the enabled ones will get a muxed adapter because this
is handled in of_i2c_register_devices()?

I am not too deep into i2c-core, but AFAIKS i2c-mux-pinctrl is not an
i2c device but an i2c mux that is dealt with differently? It is not
probed with of_i2c_register_devices() but as a separate platform_device
with a reference to the parent i2c bus.

About the memory allocation for the maximum potential number of muxes:
We would need some way to distinguish disabled from enabled muxes in
i2c-mux-pinctrl's platform_data.

i2c_mux_pinctrl_probe() is basically DT-agnostic and it should
definitely stay that way. Currently, each mux within pd->bus_count
requires a non-NULL pd->pinctrl_states[i] otherwise _probe() will bail
out for all sub-busses.

We could rework it to

(a) deal with each sub-bus individually with respect to pinctrl_lookup_state() and i2c_add_mux_adapter()


(b) allow (and skip) muxes with pinctrl_states[i] == NULL for now and
let the "maniac" deal with storing/re-probing the corresponding
pinctrl_state name once it gets dynamically enabled.

I am still not too eager working on it but if you insist, I can see
what I can do as long as Stephen sticks with testing it on Tegra. ;)

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