linux-kernel - Re: [PATCH v3 2/6] clk: Add clock driver for AXM55xx SoC

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Date:	Wed, 14 May 2014 13:08:45 -0700
From:	Mike Turquette <mturquette@...aro.org>
To:	Anders Berg <anders.berg@...gotech.com>,
	"Arnd Bergmann" <arnd@...db.de>, "Olof Johansson" <olof@...om.net>
Cc:	"Linus Walleij" <linus.walleij@...aro.org>,
	"Russell King" <linux@....linux.org.uk>,
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, "Anders Berg" <anders.berg@....com>,
	"Mark Rutland" <mark.rutland@....com>
Subject: Re: [PATCH v3 2/6] clk: Add clock driver for AXM55xx SoC

Quoting Anders Berg (2014-05-14 11:37:57)
> +Example:
> +
> +       clk_ref0: clk_ref0 {
> +               compatible = "fixed-clock";
> +               #clock-cells = <0>;
> +               clock-frequency = <125000000>;
> +       };

Hi Anders,

The driver looks good. As for the DT binding, I am starting to request
that bindings for new hardware move away from the one-clock-per-node
method. I am not forcing anyone with stable bindings to migrate that
way, but it tends to make maintenance easier in the long run (e.g.
setting per-clock flags, etc).

Your clk_ref0 example looks good, assuming that it is an off-chip clock
that feeds into the rest of the clock generator.

> +
> +       clk_cpu_pll: clk_cpu_pll@...0022000 {
> +               compatible = "lsi,axxia-pll-clock";
> +               #clock-cells = <0>;
> +               clocks = <&clk_ref0>;
> +               clock-output-names = "clk_cpu_pll";
> +               reg = <0x20 0x10022000 0 0x2c>;
> +       };

I assume the rest of your clocks are part of a clock generator IP block
inside of your chip. Have you looked at the QCOM binding? It is my
favorite binding these days. Here are some highlights:

See Documentation/devicetree/bindings/clock/qcom,gcc.txt.



>From arch/arm/boot/dts/qcom-msm8974.dtsi:

gcc: clock-controller@...00000 {
        compatible = "qcom,gcc-msm8974";
        #clock-cells = <1>;
        #reset-cells = <1>;
        reg = <0xfc400000 0x4000>;
};

...

serial@...1e000 {
        compatible = "qcom,msm-uartdm-v1.4", "qcom,msm-uartdm";
        reg = <0xf991e000 0x1000>;
        interrupts = <0 108 0x0>;
        clocks = <&gcc GCC_BLSP1_UART2_APPS_CLK>, <&gcc GCC_BLSP1_AHB_CLK>;
        clock-names = "core", "iface";
};



>From drivers/clk/qcom/gcc-msm8974.c:

static struct clk_branch gcc_blsp1_uart2_apps_clk = {
        .halt_reg = 0x0704,
        .clkr = {
                .enable_reg = 0x0704,
                .enable_mask = BIT(0),
                .hw.init = &(struct clk_init_data){
                        .name = "gcc_blsp1_uart2_apps_clk",
                        .parent_names = (const char *[]){
                                "blsp1_uart2_apps_clk_src",
                        },
                        .num_parents = 1,
                        .flags = CLK_SET_RATE_PARENT,
                        .ops = &clk_branch2_ops,
                },
        },
};



>From include/dt-bindings/clock/qcom,gcc-msm8974.h:

#define GCC_BLSP1_UART2_APPS_CLK                                103



Using this type of binding you only need to declare your clock generator
IP node in dts, and then define a mapping in the DT include chroot. Then
you can define your per-clock data inside of your clock driver instead
of putting all of the details inside of DT.

If you have a strong reason to do it the way that you originally posted
then let me know.

Regards,
Mike
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