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Date:   Sat, 31 Dec 2016 16:10:44 +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 1/9] dt-bindings: document devicetree bindings for
 mux-controllers and mux-gpio

On 30/11/16 08:16, Peter Rosin wrote:
> Signed-off-by: Peter Rosin <peda@...ntia.se>
Bindings are still a bit of a black art to me ;)

Other than the naming of the iio-mux as discussed in the other patch
I'm happy with this. It feels like it has struck the right balance
between flexibility and complexity.  Which probably means we'll
have an application it doesn't stretch to before the day is out...

Acked-by: Jonathan Cameron <jic23@...nel.org>
> ---
>  .../devicetree/bindings/misc/mux-controller.txt    | 127 +++++++++++++++++++++
>  .../devicetree/bindings/misc/mux-gpio.txt          |  68 +++++++++++
>  MAINTAINERS                                        |   5 +
>  3 files changed, 200 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/misc/mux-controller.txt
>  create mode 100644 Documentation/devicetree/bindings/misc/mux-gpio.txt
> 
> diff --git a/Documentation/devicetree/bindings/misc/mux-controller.txt b/Documentation/devicetree/bindings/misc/mux-controller.txt
> new file mode 100644
> index 000000000000..19c36b73173e
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/misc/mux-controller.txt
> @@ -0,0 +1,127 @@
> +Common multiplexer controller bindings
> +======================================
> +
> +A multiplexer (or mux) controller will have one, or several, consumer devices
> +that uses the mux controller. Thus, a mux controller can possibly control
> +several parallel multiplexers, presumably there will be at least one
> +multiplexer needed by each consumer..
> +
> +A mux controller provides a number of states to its consumers, and the state
> +space is a simple zero-based enumeration. I.e. 0-1 for a 2-way multiplexer,
> +0-7 for an 8-way multiplexer, etc.
> +
> +
> +Consumers
> +---------
> +
> +Mux controller consumers should specify a list of mux controllers that they
> +want to use with a property containing a 'mux-ctrl-list':
> +
> +	mux-ctrl-list ::= <single-mux-ctrl> [mux-ctrl-list]
> +	single-mux-ctrl ::= <mux-ctrl-phandle> [mux-ctrl-specifier]
> +	mux-ctrl-phandle : phandle to mux controller node
> +	mux-ctrl-specifier : array of #mux-control-cells specifying the
> +			     given mux controller (controller specific)
> +
> +Mux controller properties should be named "mux-controls". The exact meaning of
> +each mux controller property must be documented in the device tree binding for
> +each consumer. An optional property "mux-control-names" may contain a list of
> +strings to label each of the mux controllers listed in the "mux-controls"
> +property.
> +
> +Drivers for devices that use more than a single mux controller can use the
> +"mux-control-names" property to map the name of the mux controller requested by
> +the mux_control_get() call to an index into the list given by the
> +"mux-controls" property.
> +
> +mux-ctrl-specifier typically encodes the chip-relative mux controller number.
> +If the mux controller chip only provides a single mux controller, the
> +mux-ctrl-specifier can typically be left out.
> +
> +Example:
> +
> +	/* One consumer of a 2-way mux controller (one GPIO-line) */
> +	mux: mux-controller {
> +		compatible = "mux-gpio";
> +		#mux-control-cells = <0>;
> +
> +		mux-gpios = <&pioA 0 GPIO_ACTIVE_HIGH>;
> +	};
> +
> +	adc-mux {
> +		compatible = "iio-mux";
> +		io-channels = <&adc 0>;
> +		io-channel-names = "parent";
> +		mux-controls = <&mux>;
> +		mux-control-names = "adc";
> +
> +		channels = "sync", "in";
> +	};
> +
> +Note that in the example above, specifying the "mux-control-names" is redundant
> +because there is only one mux controller in the list.
> +
> +	/*
> +	 * Two consumers (one for an ADC line and one for an i2c bus) of
> +	 * parallel 4-way multiplexers controlled by the same two GPIO-lines.
> +	 */
> +	mux: mux-controller {
> +		compatible = "mux-gpio";
> +		#mux-control-cells = <0>;
> +
> +		mux-gpios = <&pioA 0 GPIO_ACTIVE_HIGH>,
> +			    <&pioA 1 GPIO_ACTIVE_HIGH>;
> +	};
> +
> +	adc-mux {
> +		compatible = "iio-mux";
> +		io-channels = <&adc 0>;
> +		io-channel-names = "parent";
> +		mux-controls = <&mux>;
> +
> +		channels = "sync-1", "in", "out", "sync-2";
> +	};
> +
> +	i2c-mux {
> +		compatible = "i2c-mux-simple,mux-locked";
> +		i2c-parent = <&i2c1>;
> +		mux-controls = <&mux>;
> +
> +		#address-cells = <1>;
> +		#size-cells = <0>;
> +
> +		i2c@0 {
> +			reg = <0>;
> +			#address-cells = <1>;
> +			#size-cells = <0>;
> +
> +			ssd1307: oled@3c {
> +				/* ... */
> +			};
> +		};
> +
> +		i2c@3 {
> +			reg = <3>;
> +			#address-cells = <1>;
> +			#size-cells = <0>;
> +
> +			pca9555: pca9555@20 {
> +				/* ... */
> +			};
> +		};
> +	};
> +
> +
> +Mux controller nodes
> +--------------------
> +
> +Mux controller nodes must specify the number of cells used for the
> +specifier using the '#mux-control-cells' property.
> +
> +An example mux controller might look like this:
> +
> +	mux: adg792a@50 {
> +		compatible = "adi,adg792a";
> +		reg = <0x50>;
> +		#mux-control-cells = <1>;
> +	};
> diff --git a/Documentation/devicetree/bindings/misc/mux-gpio.txt b/Documentation/devicetree/bindings/misc/mux-gpio.txt
> new file mode 100644
> index 000000000000..2ff814f082c8
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/misc/mux-gpio.txt
> @@ -0,0 +1,68 @@
> +GPIO-based multiplexer controller bindings
> +
> +Define what GPIO pins are used to control a multiplexer. Or several
> +multiplexers, if the same pins control more than one multiplexer.
> +
> +Required properties:
> +- compatible : "mux-gpio"
> +- mux-gpios : list of gpios used to control the multiplexer, least
> +	      significant bit first.
> +- #mux-control-cells : <0>
> +* Standard mux-controller bindings as decribed in mux-controller.txt
> +
> +Optional properties:
> +- idle-state : if present, the state the mux will have when idle.
> +
> +The multiplexer state is defined as the number represented by the
> +multiplexer GPIO pins, where the first pin is the least significant
> +bit. An active pin is a binary 1, an inactive pin is a binary 0.
> +
> +Example:
> +
> +	mux: mux-controller {
> +		compatible = "mux-gpio";
> +		#mux-control-cells = <0>;
> +
> +		mux-gpios = <&pioA 0 GPIO_ACTIVE_HIGH>,
> +			    <&pioA 1 GPIO_ACTIVE_HIGH>;
> +	};
> +
> +	adc-mux {
> +		compatible = "iio-mux";
> +		io-channels = <&adc 0>;
> +		io-channel-names = "parent";
> +
> +		mux-controls = <&mux>;
> +
> +		channels = "sync-1", "in", "out", "sync-2";
> +	};
> +
> +	i2c-mux {
> +		compatible = "i2c-mux-simple,mux-locked";
> +		i2c-parent = <&i2c1>;
> +
> +		mux-controls = <&mux>;
> +
> +		#address-cells = <1>;
> +		#size-cells = <0>;
> +
> +		i2c@0 {
> +			reg = <0>;
> +			#address-cells = <1>;
> +			#size-cells = <0>;
> +
> +			ssd1307: oled@3c {
> +				/* ... */
> +			};
> +		};
> +
> +		i2c@3 {
> +			reg = <3>;
> +			#address-cells = <1>;
> +			#size-cells = <0>;
> +
> +			pca9555: pca9555@20 {
> +				/* ... */
> +			};
> +		};
> +	};
> diff --git a/MAINTAINERS b/MAINTAINERS
> index d8eb3843dbd4..3d4d0efc2b64 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -8403,6 +8403,11 @@ S:	Orphan
>  F:	drivers/mmc/host/mmc_spi.c
>  F:	include/linux/spi/mmc_spi.h
>  
> +MULTIPLEXER SUBSYSTEM
> +M:	Peter Rosin <peda@...ntia.se>
> +S:	Maintained
> +F:	Documentation/devicetree/bindings/misc/mux-*
> +
>  MULTISOUND SOUND DRIVER
>  M:	Andrew Veliath <andrewtv@....net>
>  S:	Maintained
> 

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