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

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Date:	Mon, 02 Mar 2015 13:01:09 -0700
From:	Stephen Warren <swarren@...dotorg.org>
To:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
CC:	Jason Cooper <jason@...edaemon.net>, Andrew Lunn <andrew@...n.ch>,
	Gregory Clement <gregory.clement@...e-electrons.com>,
	Gabriel Dobato <dobatog@...il.com>,
	Wolfram Sang <wsa@...-dreams.de>, linux-i2c@...r.kernel.org,
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [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 
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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