linux-kernel - Re: [PATCH v2 2/3] dt-bindings: clk: add documentation for the SiFive PRCI driver

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Date:   Wed, 24 Oct 2018 13:47:57 -0500
From:   Rob Herring <robh@...nel.org>
To:     Paul Walmsley <paul.walmsley@...ive.com>
Cc:     linux-clk@...r.kernel.org, devicetree@...r.kernel.org,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Palmer Dabbelt <palmer@...ive.com>,
        Megan Wachs <megan@...ive.com>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Paul Walmsley <paul@...an.com>
Subject: Re: [PATCH v2 2/3] dt-bindings: clk: add documentation for the
 SiFive PRCI driver

On Sat, Oct 20, 2018 at 06:50:23AM -0700, Paul Walmsley wrote:
> Add DT binding documentation for the Linux driver for the SiFive
> PRCI clock & reset control IP block, as found on the SiFive
> FU540 chip.
> 
> Cc: Michael Turquette <mturquette@...libre.com>
> Cc: Stephen Boyd <sboyd@...nel.org>
> Cc: Rob Herring <robh+dt@...nel.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Palmer Dabbelt <palmer@...ive.com>
> Cc: Megan Wachs <megan@...ive.com>
> Cc: linux-clk@...r.kernel.org
> Cc: devicetree@...r.kernel.org
> Cc: linux-riscv@...ts.infradead.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Paul Walmsley <paul.walmsley@...ive.com>
> Signed-off-by: Paul Walmsley <paul@...an.com>
> ---
> v2: remove out-of-date example, add documentation for the compatible
>     string and for the required PCB clock nodes
> 
> .../bindings/clock/sifive/fu540-prci.txt      | 43 +++++++++++++++++++
>  1 file changed, 43 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/clock/sifive/fu540-prci.txt
> 
> diff --git a/Documentation/devicetree/bindings/clock/sifive/fu540-prci.txt b/Documentation/devicetree/bindings/clock/sifive/fu540-prci.txt
> new file mode 100644
> index 000000000000..d7c1e83fa5ed
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/clock/sifive/fu540-prci.txt
> @@ -0,0 +1,43 @@
> +SiFive FU540 PRCI bindings
> +
> +On the FU540 family of SoCs, most system-wide clock and reset integration
> +is via the PRCI IP block.
> +
> +Required properties:
> +- compatible: Should be "sifive,<chip>-prci<version>".  As of the time this
> +              file was written, only one value is supported:
> +	      "sifive,fu540-c000-prci0"

What happens with this depends on the discussion on the other bindings.

Though here you are inconsistent without a fallback. Of course, I've 
never seen a clock controller be the same across SoCs.

> +- reg: Should describe the PRCI's register target physical address region
> +- clocks: Should point to the hfclk device tree node and the rtcclk
> +          device tree node.  The RTC clock here is not a time-of-day clock,
> +	  but is instead a high-stability clock source for system timers
> +	  and cycle counters.
> +- #clock-cells: Should be <1>
> +
> +The clock consumer should specify the desired clock via the clock ID
> +macros defined in include/linux/clk/sifive-fu540-prci.h.  These macros
> +begin with PRCI_CLK_.
> +
> +The hfclk and rtcclk nodes are required, and represent physical
> +crystals or resonators located on the PCB.
> +
> +Examples:
> +
> +hfclk: hfclk {
> +	#clock-cells = <0>;
> +	compatible = "fixed-clock";
> +	clock-frequency = <33333333>;
> +	clock-output-names = "hfclk";
> +};
> +rtcclk: rtcclk {
> +	#clock-cells = <0>;
> +	compatible = "fixed-clock";
> +	clock-frequency = <1000000>;
> +	clock-output-names = "rtcclk";
> +};
> +prci0: prci@...00000 {

clock-controller@...

> +	compatible = "sifive,fu540-c000-prci0";
> +	reg = <0x0 0x10000000 0x0 0x1000>;
> +	clocks = <&hfclk>, <&rtcclk>;
> +	#clock-cells = <1>;
> +};
> -- 
> 2.19.1
>