Re: [PATCH 1/8] i2c: mux-pinctrl: Rework to honor disabled child nodes

From: Sebastian Hesselbarth
Date: Tue Feb 17 2015 - 16:08:20 EST

On 17.02.2015 21:46, Stephen Warren wrote:
On 02/17/2015 11:52 AM, Sebastian Hesselbarth wrote:
I2C mux pinctrl driver currently determines the number of sub-busses by
counting available pinctrl-names. Unfortunately, this requires each
incarnation of the devicetree node with different available sub-busses
to be rewritten.

Can you be more explicit about the problem here? Why does anything need
to be re-written if a child node is disabled; presumably there's no need
for the child bus numbers to be contiguous. In other words, with the
example in the existing DT binding doc:

i2cmux {
compatible = "i2c-mux-pinctrl";
pinctrl-names = "ddc", "pta", "idle";
pinctrl-0 = <&state_i2cmux_ddc>;
pinctrl-1 = <&state_i2cmux_pta>;
pinctrl-2 = <&state_i2cmux_idle>;

i2c@0 {
reg = <0>;
i2c@1 {
reg = <1>;

That would generate child busses 0 and 1. If I was to disable the i2c@0
node, then there would still be definitions for child busses 0 and 1 in
the DT, it's just that child bus 0 wouldn't actually exist at run-time.
I don't see what part of DT needs to be re-written to accomodate this?

The way the current driver works, to disable i2c@0 you'd have to remove
the pinctrl-0 state, pinctrl-names string at position 0, and the node

So, on Dove SoC there is three sub-busses, now consider one board A with
i2c0 and i2c1 enabled but board B with i2c0 and i2c2 enabled:


i2cmux {
pinctrl-names = "i2c0", "i2c1", "idle";
pinctrl-0 = <&state_for_i2c0>;
pinctrl-1 = <&state_for_i2c1>;



i2cmux {
pinctrl-names = "i2c0", "i2c2", "idle";
pinctrl-0 = <&state_for_i2c0>;
pinctrl-1 = <&state_for_i2c2>;
/* Note that this ^^^ is state_for_i2c2 */

while the approach with status = "disabled" allows all properties for
both board remain the same - except you'll enable either i2c1 or i2c2
sub-node on board level:

i2cmux {
pinctrl-names = "i2c0", "i2c1", "i2c2", "idle";
pinctrl-0 = <&state_for_i2c0>;
pinctrl-1 = <&state_for_i2c1>;
pinctrl-2 = <&state_for_i2c2>;


i2cmux {
i2c@0 { status = "okay"; };
i2c@1 { status = "okay"; };



i2cmux {
i2c@0 { status = "okay"; };
i2c@2 { status = "okay"; };

In general, it is less about the binding but how the driver is written:
Number of sub-busses is determined by elements in pinctrl-names not
available (enabled) sub-nodes.

This patch reworks i2c-mux-pinctrl driver to count the number of
available sub-nodes instead. The rework should be compatible to the old
way of probing for sub-busses and additionally allows to disable unused
sub-busses with standard DT property status = "disabled".

This also amends the corresponding devicetree binding documentation to
reflect the new functionality to disable unused sub-nodes. While at it,
also fix two references to binding documentation files that miss an

diff --git a/Documentation/devicetree/bindings/i2c/i2c-mux-pinctrl.txt

-For each named state defined in the pinctrl-names property, an I2C
child bus
-will be created. I2C child bus numbers are assigned based on the
index into
-the pinctrl-names property.
+For each child node that is not disabled by a status != "okay", an I2C
+child bus will be created. I2C child bus numbers are assigned based
on the
+order of child nodes.

I would have assumed that disabled sub-nodes was a global concept within
DT, and so wouldn't be mentioned in the binding. It would just be a bug
in the driver if it didn't ignore disabled sub-nodes.

Yep, the concept is very global. It is about the current driver and this
binding changes are just to make it a little more clear that the driver
should behave different, i.e. get rid of anything that implies that
pinctrl-names has any effect on the number of sub-busses registered.

-The only exception is that no bus will be created for a state named
"idle". If
-such a state is defined, it must be the last entry in pinctrl-names. For
- pinctrl-names = "ddc", "pta", "idle" -> ddc = bus 0, pta = bus 1
- pinctrl-names = "ddc", "idle", "pta" -> Invalid ("idle" not last)
- pinctrl-names = "idle", "ddc", "pta" -> Invalid ("idle" not last)
+There must be a corresponding pinctrl-names entry for each enabled child
+node at the position of the child node's "reg" property.

The addition there seems fine, but the existing text re: the idle state
seems clearer in the original text.

Ok, I'll have a look at how to preserve this section better.

Do you still have one of the current boards available for testing?

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