linux-kernel - Re: [PATCH v6 8/9] dt-bindings: mux-adg792a: document devicetree bindings for ADG792A/G mux

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Date:   Sun, 1 Jan 2017 11:00:30 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Peter Rosin <peda@...ntia.se>, linux-kernel@...r.kernel.org
Cc:     Wolfram Sang <wsa@...-dreams.de>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Jonathan Corbet <corbet@....net>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-i2c@...r.kernel.org, devicetree@...r.kernel.org,
        linux-iio@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v6 8/9] dt-bindings: mux-adg792a: document devicetree
 bindings for ADG792A/G mux

On 30/11/16 08:17, Peter Rosin wrote:
> Analog Devices ADG792A/G is a triple 4:1 mux.
> 
> Signed-off-by: Peter Rosin <peda@...ntia.se>
Few comments inline.  Worth adding anything about the gpio (output pins) to
the binding at this stage as well?  Would certainly be nice to support
them.

Jonathan
> ---
>  .../devicetree/bindings/misc/mux-adg792a.txt       | 64 ++++++++++++++++++++++
>  1 file changed, 64 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/misc/mux-adg792a.txt
> 
> diff --git a/Documentation/devicetree/bindings/misc/mux-adg792a.txt b/Documentation/devicetree/bindings/misc/mux-adg792a.txt
> new file mode 100644
> index 000000000000..4677f9ab1c55
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/misc/mux-adg792a.txt
> @@ -0,0 +1,64 @@
> +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:
> +- adi,parallel : if present, the three muxes are bound together with a single
> +  mux controller, controlling all three muxes in parallel.
> +- adi,idle-state : if present, array of states the three mux controllers will
> +  have when idle (or, if parallel, a single idle-state).
Hmm. These are actually a policy decision.  As only one policy will make
sense for a given set of hardware probably fine to have it in here I guess.
Might be worth adding a note to say this though.
> +
> +Mux controller states 0 through 3 correspond to signals A through D in the
> +datasheet. Mux controller states 4 and 5 are only available as possible idle
> +states. State 4 represents that nothing is connected, and state 5 represents
> +that the mux controller keeps the mux in its previously selected state during
> +the idle period. State 5 is the default idle state.
I'm never a great fan of magic numbers.  Can we represent this more cleanly by
breaking it into multiple properties?
Optional:
adi,idle-switch-to-channel : switch to this channel when idle.
adi,idle-high-impedance : <boolean> the nothing connected state?

If neither present leaves it in previous state?
> +
> +Example:
> +
> +	/* three independent mux controllers (of which one is used) */
> +	&i2c0 {
> +		mux: adg792a@50 {
> +			compatible = "adi,adg792a";
> +			reg = <0x50>;
> +			#mux-control-cells = <1>;
> +		};
> +	};
> +
> +	adc-mux {
> +		compatible = "iio-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 = "iio-mux";
> +		io-channels = <&adc 0>;
> +		io-channel-names = "parent";
> +
> +		mux-controls = <&pmux>;
> +
> +		channels = "sync-1", "", "out";
> +	};
>