On 17.02.2015 21:46, Stephen Warren wrote:

On 02/17/2015 11:52 AM, Sebastian Hesselbarth wrote:

quoted

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 at 0 {
                         reg = <0>;
...
                 i2c at 1 {
                         reg = <1>;
...

That would generate child busses 0 and 1. If I was to disable the i2c at 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 at 0 you'd have to remove
the pinctrl-0 state, pinctrl-names string at position 0, and the node
itself.

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:

board-A.dts:

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

but

board-B.dts:

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>;
};

board-A.dts:

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

and

board-B.dts:

i2cmux {
	i2c at 0 { status = "okay"; };
	i2c at 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.

quoted

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
"i2c-"
prefix.

quoted

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

b/Documentation/devicetree/bindings/i2c/i2c-mux-pinctrl.txt

quoted

-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.

quoted

-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
-example:
-
-    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?

Sebastian