linux-kernel - Re: [PATCH v6 3/6] dt-bindings: clock: renesas,rzn1-clocks: document RZ/N1 clock driver

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Message-ID: <20180522160913.GA7755@rob-hp-laptop>
Date:   Tue, 22 May 2018 11:09:13 -0500
From:   Rob Herring <robh@...nel.org>
To:     Michel Pollet <michel.pollet@...renesas.com>
Cc:     linux-renesas-soc@...r.kernel.org,
        Simon Horman <horms@...ge.net.au>, phil.edworthy@...esas.com,
        Michel Pollet <buserror+upstream@...il.com>,
        Magnus Damm <magnus.damm@...il.com>,
        Mark Rutland <mark.rutland@....com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-clk@...r.kernel.org
Subject: Re: [PATCH v6 3/6] dt-bindings: clock: renesas,rzn1-clocks: document
 RZ/N1 clock driver

On Tue, May 22, 2018 at 11:01:23AM +0100, Michel Pollet wrote:
> The Renesas RZ/N1 Family (Part #R9A06G0xx) requires a driver
> to provide the SoC clock infrastructure for Linux.
> 
> This documents the driver bindings.
> 
> Signed-off-by: Michel Pollet <michel.pollet@...renesas.com>
> ---
>  .../bindings/clock/renesas,rzn1-clocks.txt         | 44 ++++++++++++++++++++++
>  1 file changed, 44 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/clock/renesas,rzn1-clocks.txt
> 
> diff --git a/Documentation/devicetree/bindings/clock/renesas,rzn1-clocks.txt b/Documentation/devicetree/bindings/clock/renesas,rzn1-clocks.txt
> new file mode 100644
> index 0000000..0c41137
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/clock/renesas,rzn1-clocks.txt
> @@ -0,0 +1,44 @@
> +* Renesas RZ/N1 Clock Driver
> +
> +This driver provides the clock infrastructure used by all the other drivers.

Bindings document h/w not drivers.

> +
> +One of the 'special' feature of this infrastructure is that Linux doesn't

Bindings are not just for Linux.

> +necessary 'own' all the clocks on the SoC, some other OS runs on
> +the Cortex-M3 core and that OS can access and claim it's own clocks.

How is this relevant to the binding?

> +
> +Required Properties:
> +
> +  - compatible: Must be
> +    - "renesas,r9a06g032-clocks" for the RZ/N1D
> +    and "renesas,rzn1-clocks" as a fallback.

Is "clocks" how the chip reference manual refers to this block?

> +  - reg: Base address and length of the memory resource used by the driver
> +  - #clock-cells: Must be 1
> +
> +Examples
> +--------
> +
> +  - Clock driver device node:
> +
> +	clock: clocks@...0c000 {

clock-controller@...

> +		compatible = "renesas,r9a06g032-clocks",
> +				"renesas,rzn1-clocks";
> +		reg = <0x4000c000 0x1000>;
> +		status = "okay";

Don't show status in examples. (Plus, I doubt you ever want to have this 
disabled, so you don't need the property in your dts files either).

> +		#clock-cells = <1>;
> +	};
> +
> +
> +  - Other drivers can use the clocks as in:

s/drivers/nodes/

> +
> +	uart0: serial@...60000 {
> +		compatible = "snps,dw-apb-uart";
> +		reg = <0x40060000 0x400>;
> +		interrupts = <GIC_SPI 6 IRQ_TYPE_LEVEL_HIGH>;
> +		reg-shift = <2>;
> +		reg-io-width = <4>;
> +		clocks = <&clock RZN1_CLK_UART0>;
> +		clock-names = "baudclk";
> +	};
> +    Note the use of RZN1_CLK_UART0 -- these constants are declared in
> +    the rzn1-clocks.h header file. These are not hardware based constants
> +    and are Linux specific.

No, they are not Linux specific. They are part of the DT ABI. 

While it is not a requirement to base them on some h/w numbering, it is 
preferred if you can. That usually only works if you can base them on 
bit positions or register offsets.

Rob