Re: [PATCH v2 1/4] i2c: mux-pinctrl: Rework to honor disabled child nodes

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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 binding.

-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 description.

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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