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SubjectRe: [PATCH v2 1/4] i2c: mux-pinctrl: Rework to honor disabled child nodes
On 02/27/2015 05:24 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.
> 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.

> diff --git a/Documentation/devicetree/bindings/i2c/i2c-mux-pinctrl.txt b/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 enabled child node an I2C child bus will be created. I2C child bus
> +numbers are assigned based on the order of child nodes.

I think that I2C bus numbers are an internal concept for the OS. As
such, we should probably remove any mention re: the bus numbers from the

> -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:
> +There must be a corresponding pinctrl-names entry for each enabled child
> +node at the position of the child node's "reg" property. Also, there can be
> +an idle pinctrl state defined at the end of possible pinctrl states. If such
> +a state is defined, it must be the last entry in pinctrl-names. For example:

What about gaps in the numbering sequence? IIRC, in a situation with 5
nodes with reg 0, 1, 2, 3, 4 but where only the nodes with reg of 1, 3
enabled, we only want 2 entries in pinctrl-names? If so, "at the
position of the child node's "reg" property" isn't correct, since "at
the position" implies there must be gaps in pinctrl-names. "In the same
order as the reg property values for enabled subnodes" might be a better

Perhaps I'm misremembering and you explicitly didn't want to remove
entries from pinctrl-names if child nodes were disabled? If so, then
surely then in the text above, "for each enabled child" should be
replaced with "for each child"?

> @@ -68,6 +68,7 @@ Example:
> pinctrl-1 = <&state_i2cmux_pta>;
> pinctrl-2 = <&state_i2cmux_idle>;
> + /* Enabled child bus 0 */
> i2c@0 {
> reg = <0>;
> #address-cells = <1>;
> @@ -79,10 +80,12 @@ Example:
> };
> };
> + /* Disabled child bus 1 */
> i2c@1 {
> reg = <1>;
> #address-cells = <1>;
> #size-cells = <0>;
> + status = "disabled";

To make the example cover more cases, perhaps make child node i2c@0
disabled and i2c@1 enabled. Then, the example would show what happens to
pinctrl-names when there are gaps in the reg property numbering space of
enabled children?

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