linux-kernel - Re: [PATCH 02/48] ARM: at91: Document new TCB bindings

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Date:	Tue, 14 Jun 2016 16:47:37 -0500
From:	Rob Herring <robh@...nel.org>
To:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Cc:	Nicolas Ferre <nicolas.ferre@...el.com>,
	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Thierry Reding <thierry.reding@...il.com>,
	linux-pwm@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH 02/48] ARM: at91: Document new TCB bindings

On Sat, Jun 11, 2016 at 12:03:05AM +0200, Alexandre Belloni wrote:
> The current binding for the TCB is not flexible enough for some use cases
> and prevents proper utilization of all the channels.
> 
> Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
> Cc: Thierry Reding <thierry.reding@...il.com>
> Cc: linux-pwm@...r.kernel.org
> Cc: Rob Herring <robh+dt@...nel.org>
> Cc: devicetree@...r.kernel.org
> Signed-off-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>
> ---
>  .../devicetree/bindings/arm/atmel-at91.txt         | 32 -----------
>  .../devicetree/bindings/mfd/atmel-tcb.txt          | 62 ++++++++++++++++++++++
>  .../devicetree/bindings/pwm/atmel-tcb-pwm.txt      | 12 +++--
>  3 files changed, 69 insertions(+), 37 deletions(-)
>  create mode 100644 Documentation/devicetree/bindings/mfd/atmel-tcb.txt

[...]

> diff --git a/Documentation/devicetree/bindings/mfd/atmel-tcb.txt b/Documentation/devicetree/bindings/mfd/atmel-tcb.txt
> new file mode 100644
> index 000000000000..48196752c78f
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/mfd/atmel-tcb.txt
> @@ -0,0 +1,62 @@
> +* Device tree bindings for Atmel Timer Counter Blocks
> +- compatible: Should be "atmel,<chip>-tcb", "simple-mfd", "syscon".
> +  <chip> can be "at91rm9200" or "at91sam9x5"
> +- reg: Should contain registers location and length
> +- #address-cells: has to be 1
> +- #size-cells: has to be 0
> +- interrupts: Should contain all interrupts for the TC block
> +  Note that you can specify several interrupt cells if the TC
> +  block has one interrupt per channel.
> +- clock-names: tuple listing input clock names.
> +	Required elements: "t0_clk", "slow_clk"
> +	Optional elements: "t1_clk", "t2_clk"
> +- clocks: phandles to input clocks.

What is the order of clocks?

> +
> +The TCB can expose multiple subdevices:
> + * a clocksource and clockevent device

No. These compatible names are linuxisms. Describe features of the 
timers to be able to select which timer to use if you need to pick 
certain timers. For example, interrupt capability could be used to 
select the clkevt.

> +   - compatible: Should be "atmel,tcb-clksrc"
> +   - reg: Should contain the TCB channels to be used. If the
> +     counter width is 16 bits (at91rm9200-tcb), two consecutive
> +     channels are needed. Else, only one channel will be used.
> +
> + * a clockevent device
> +   - compatible: Should be "atmel,tcb-clkevt"
> +   - reg: Should contain the TCB channel to be used
> +
> + * a PWM chip: see ../pwm/atmel-tcb-pwm.txt
> +
> +Examples:
> +
> +One interrupt per TC block:
> +	tcb0: timer@...7c000 {
> +		compatible = "atmel,at91rm9200-tcb", "simple-mfd", "syscon";
> +		#address-cells = <1>;
> +		#size-cells = <0>;
> +		reg = <0xfff7c000 0x100>;
> +		interrupts = <18 4>;
> +		clocks = <&tcb0_clk>;
> +		clock-names = "t0_clk";

Missing slow_clk

> +
> +		timer@0 {
> +			compatible = "atmel,tcb-clksrc";
> +			reg = <0>, <1>;
> +		};
> +
> +		timer@2 {
> +			compatible = "atmel,tcb-clkevt";
> +			reg = <2>;
> +		};
> +	};
> +
> +One interrupt per TC channel in a TC block:
> +	tcb1: timer@...dc000 {
> +		compatible = "atmel,at91rm9200-tcb", "simple-mfd", "syscon";
> +		#address-cells = <1>;
> +		#size-cells = <0>;
> +		reg = <0xfffdc000 0x100>;
> +		interrupts = <26 4>, <27 4>, <28 4>;
> +		clocks = <&tcb1_clk>;
> +		clock-names = "t0_clk";
> +	};
> +
> +
> diff --git a/Documentation/devicetree/bindings/pwm/atmel-tcb-pwm.txt b/Documentation/devicetree/bindings/pwm/atmel-tcb-pwm.txt
> index 8031148bcf85..ab8fbd5ba184 100644
> --- a/Documentation/devicetree/bindings/pwm/atmel-tcb-pwm.txt
> +++ b/Documentation/devicetree/bindings/pwm/atmel-tcb-pwm.txt
> @@ -2,15 +2,17 @@ Atmel TCB PWM controller
>  
>  Required properties:
>  - compatible: should be "atmel,tcb-pwm"
> +- reg: tcb channel to use. Each channel can export 2 PWMs

Is there a difference in channels? If not, then this compatible should 
go.

>  - #pwm-cells: should be 3. See pwm.txt in this directory for a description of
>    the cells format. The only third cell flag supported by this binding is
>    PWM_POLARITY_INVERTED.
> -- tc-block: The Timer Counter block to use as a PWM chip.
>  
>  Example:
>  
> -pwm {
> -	compatible = "atmel,tcb-pwm";
> -	#pwm-cells = <3>;
> -	tc-block = <1>;
> +tcb0: timer@...0c000 {
> +	pwm@0 {
> +		compatible = "atmel,tcb-pwm";
> +		reg = <0>;
> +		#pwm-cells = <3>;
> +	};
>  };
> -- 
> 2.8.1
>