linux-kernel - Re: [PATCH v8 09/12] dt-bindings: mux-adg792a: document devicetree bindings for ADG792A/G mux

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Date:   Fri, 27 Jan 2017 23:09:53 +0100
From:   Peter Rosin <peda@...ntia.se>
To:     Rob Herring <robh@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Wolfram Sang <wsa@...-dreams.de>,
        Mark Rutland <mark.rutland@....com>,
        Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Jonathan Corbet <corbet@....net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-i2c@...r.kernel.org, devicetree@...r.kernel.org,
        linux-iio@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v8 09/12] dt-bindings: mux-adg792a: document devicetree
 bindings for ADG792A/G mux

On 2017-01-27 20:50, Rob Herring wrote:
> On Wed, Jan 18, 2017 at 04:57:12PM +0100, Peter Rosin wrote:
>> Analog Devices ADG792A/G is a triple 4:1 mux.
>>
>> Acked-by: Jonathan Cameron <jic23@...nel.org>
>> Signed-off-by: Peter Rosin <peda@...ntia.se>
>> ---
>>  .../devicetree/bindings/mux/mux-adg792a.txt        | 79 ++++++++++++++++++++++
>>  1 file changed, 79 insertions(+)
>>  create mode 100644 Documentation/devicetree/bindings/mux/mux-adg792a.txt
>>
>> diff --git a/Documentation/devicetree/bindings/mux/mux-adg792a.txt b/Documentation/devicetree/bindings/mux/mux-adg792a.txt
>> new file mode 100644
>> index 000000000000..0b26dd11f070
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/mux/mux-adg792a.txt
>> @@ -0,0 +1,79 @@
>> +Bindings for Analog Devices ADG792A/G Triple 4:1 Multiplexers
>> +
>> +Required properties:
>> +- compatible : "adi,adg792a" or "adi,adg792g"
>> +- #mux-control-cells : <0> if parallel, or <1> if not.
>> +* Standard mux-controller bindings as decribed in mux-controller.txt
>> +
>> +Optional properties for ADG792G:
>> +- gpio-controller : if present, #gpio-cells below is required.
>> +- #gpio-cells : should be <2>
>> +			  - First cell is the GPO line number, i.e. 0 or 1
>> +			  - Second cell is used to specify active high (0)
>> +			    or active low (1)
>> +
>> +Optional properties:
>> +- adi,parallel : if present, the three muxes are bound together with a single
>> +  mux controller, controlling all three muxes in parallel.
> 
> Can't this be implied by #mux-control-cells == 0?

Right, good point! I'll drop adi,parallel.

>> +- adi,idle-state : if present, array of 2-tuples with mux controller number
>> +  and state that mux controllers will have when idle. States 0 through 3
>> +  correspond to signals A through D in the datasheet.
>> +- adi,idle-high-impedance : if present, array of mux controller numbers that
>> +  should be in the disconnected high-impedance state when idle.
> 
> Perhaps combine these 2 to a common idle-state with the index being the 
> mux controller number and a value of -1 (or 4) being hi-Z.

At one point [1] I had a straight array for the mux controllers with state 4
being hi-Z and state 5 being the default "leave mux as-is on release", but
Jonathan didn't like magic numbers. Can you please read the follow-ups to the
referenced mail for some background, and then pick out the most suitable color
for me to paint with? :-)

[1] https://lkml.org/lkml/2016/11/30/110

>> +
>> +Mux controller states 0 through 3 correspond to signals A through D in the
>> +datasheet. If a mux controller is mentioned in neither adi,idle-state nor
>> +adi,idle-high-impedance it is left in its previously selected state when idle.
>> +
>> +Example:
>> +
>> +	/*
>> +	 * Three independent mux controllers (of which one is used).
>> +	 * Mux 0 is disconnected when idle, mux 1 idles with signal C
>> +	 * and mux 2 idles with signal A.
>> +	 */
>> +	&i2c0 {
>> +		mux: adg792a@50 {
> 
> mux-controller@50

Yep. Hmm, where have I seen that before? :-)

Cheers,
peda

>> +			compatible = "adi,adg792a";
>> +			reg = <0x50>;
>> +			#mux-control-cells = <1>;
>> +
>> +			adi,idle-high-impedance = <0>;
>> +			adi,idle-state = <1 2>, <2 0>;
>> +		};
>> +	};
>> +
>> +	adc-mux {
>> +		compatible = "io-channel-mux";
>> +		io-channels = <&adc 0>;
>> +		io-channel-names = "parent";
>> +
>> +		mux-controls = <&mux 1>;
>> +
>> +		channels = "sync-1", "", "out";
>> +	};
>> +
>> +
>> +	/*
>> +	 * Three parallel muxes with one mux controller, useful e.g. if
>> +	 * the adc is differential, thus needing two signals to be muxed
>> +	 * simultaneously for correct operation.
>> +	 */
>> +	&i2c0 {
>> +		pmux: adg792a@50 {
>> +			compatible = "adi,adg792a";
>> +			reg = <0x50>;
>> +			#mux-control-cells = <0>;
>> +			adi,parallel;
>> +		};
>> +	};
>> +
>> +	diff-adc-mux {
>> +		compatible = "io-channel-mux";
>> +		io-channels = <&adc 0>;
>> +		io-channel-names = "parent";
>> +
>> +		mux-controls = <&pmux>;
>> +
>> +		channels = "sync-1", "", "out";
>> +	};
>> -- 
>> 2.1.4
>>
>> --
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