Re: [PATCH 3/7] dt-bindings: i2c: add support for 'i2c-gate' subnode

[Peter Rosin <peda@axentia.se>]

On 2016-07-29 23:25, Rob Herring wrote:
> On Wed, Jul 27, 2016 at 10:43:26AM +0200, Peter Rosin wrote:
>> Handle i2c gates similarly to how i2c arbitrators are handled.
>> This gets rid of a pointless 'reg' property for i2c gates.
>>
>> I.e. this new and more compact style
>>
>>         some-gate {
>>                 i2c-gate {
>>                         #address-cells = <1>;
>>                         #size-cells = <0>;
>>
>>                         some-i2c-device@50 {
>>                                 reg = <0x50>;
>>                         };
>>                 };
>>         };
>>
>> instead of the old
>>
>>         some-gate {
>>                 #address-cells = <1>;
>>                 #size-cells = <0>;
>>
>>                 i2c@0 {
>>                         reg = <0>;
>>
>>                         #address-cells = <1>;
>>                         #size-cells = <0>;
>>
>>                         some-i2c-device@50 {
>>                                 reg = <0x50>;
>>                         };
>>                 };
>>         };
>>
>> Signed-off-by: Peter Rosin <peda@axentia.se>
>> ---
>>  Documentation/devicetree/bindings/i2c/i2c-gate.txt | 35 ++++++++++++++++++++++
>>  MAINTAINERS                                        |  1 +
>>  2 files changed, 36 insertions(+)
>>  create mode 100644 Documentation/devicetree/bindings/i2c/i2c-gate.txt
>>
>> diff --git a/Documentation/devicetree/bindings/i2c/i2c-gate.txt b/Documentation/devicetree/bindings/i2c/i2c-gate.txt
>> new file mode 100644
>> index 000000000000..78f17892dfc6
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/i2c/i2c-gate.txt
>> @@ -0,0 +1,35 @@
>> +Common i2c gate properties.
> 
> Perhaps define what a gate is.

How about the following paragraph at the very top of the file?

An i2c gate is useful to e.g. reduce the digital noise for RF tuners connected
to the i2c bus. Gates are similar to arbitrators in that you need to perform
some kind of operation to access the i2c bus past the arbitrator/gate, but
there are no competing masters to consider for gates and therefore there is
no arbitration happening for gates.

>> +
>> +- i2c-gate child node
>> +
>> +Required properties for the i2c-gate child node:
>> +- #address-cells = <1>;
>> +- #size-cells = <0>;
>> +
>> +Optional properties for i2c-gate child node:
>> +- Child nodes conforming to i2c bus binding
>> +
>> +
>> +Example :
>> +
>> +	/*
>> +	   An Invensense mpu9150 at address 0x68 featuring an on-chip Asahi
>> +	   Kasei ak8975 compass behind a gate.
>> +	 */
>> +
>> +	mpu9150@68 {
>> +		compatible = "invensense,mpu9150";
>> +		reg = <0x68>;
>> +		interrupt-parent = <&gpio1>;
>> +		interrupts = <18 1>;
>> +
>> +		i2c-gate {
>> +			#address-cells = <1>;
>> +			#size-cells = <0>;
>> +
>> +			ax8975@0c {
>> +				compatible = "ak,ak8975";
>> +				reg = <0x0c>;
>> +			};
>> +		};
>> +	};
>> diff --git a/MAINTAINERS b/MAINTAINERS
>> index 543052305a09..0e6cc071c480 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -5525,6 +5525,7 @@ F:	Documentation/i2c/i2c-topology
>>  F:	Documentation/i2c/muxes/
>>  F:	Documentation/devicetree/bindings/i2c/i2c-mux*
>>  F:	Documentation/devicetree/bindings/i2c/i2c-arb*
>> +F:	Documentation/devicetree/bindings/i2c/i2c-gate*
>>  F:	drivers/i2c/i2c-mux.c
>>  F:	drivers/i2c/muxes/
>>  F:	include/linux/i2c-mux.h
>> -- 
>> 2.1.4
>>