Re: [PATCH v4] clk: Add PWM clock driver

Janusz Użycki
2014-12-12T19:22:11Z

W dniu 2014-12-12 o 11:47, Philipp Zabel pisze:
> Some board designers, when running out of clock output pads, decide to
> (mis)use PWM output pads to provide a clock to external components.
> This driver supports this practice by providing an adapter between the
> PWM and clock bindings in the device tree. As the PWM bindings specify
> the period in the device tree, this is a fixed clock.
>
> Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
> ---
> Changes since v3:
> - Call pwm_enable/disable from prepare/unprepare callbacks
> - Use NSEC_PER_SEC
> - Add CLK_IS_BASIC flag
> - Register clk_pwm_remove function
> - Since this is a platform_device, remove driver.owner = THIS_MODULE
> ---
> .../devicetree/bindings/clock/pwm-clock.txt | 26 +++++
> drivers/clk/Kconfig | 7 ++
> drivers/clk/Makefile | 1 +
> drivers/clk/clk-pwm.c | 129 +++++++++++++++++++++
> 4 files changed, 163 insertions(+)
> create mode 100644 Documentation/devicetree/bindings/clock/pwm-clock.txt
> create mode 100644 drivers/clk/clk-pwm.c
>
> diff --git a/Documentation/devicetree/bindings/clock/pwm-clock.txt b/Documentation/devicetree/bindings/clock/pwm-clock.txt
> new file mode 100644
> index 0000000..751fff5
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/clock/pwm-clock.txt
> @@ -0,0 +1,26 @@
> +Binding for an external clock signal driven by a PWM pin.
> +
> +This binding uses the common clock binding[1] and the common PWM binding[2].
> +
> +[1] Documentation/devicetree/bindings/clock/clock-bindings.txt
> +[2] Documentation/devicetree/bindings/pwm/pwm.txt
> +
> +Required properties:
> +- compatible : shall be "pwm-clock".
> +- #clock-cells : from common clock binding; shall be set to 0.
> +- pwms : from common PWM binding; this determines the clock frequency
> + via the PWM period given in the pwm-specifier.
> +
> +Optional properties:
> +- clock-output-names : From common clock binding.
> +- clock-frequency : Exact output frequency, in case the pwm period
> + is not exact but was rounded to nanoseconds.
> +
> +Example:
> + clock {
> + compatible = "pwm-clock";
> + #clock-cells = <0>;
> + clock-frequency = <25000000>;
> + clock-output-names = "mipi_mclk";
> + pwms = <&pwm2 0 40>; /* 1 / 40 ns = 25 MHz */
> + };
> diff --git a/drivers/clk/Kconfig b/drivers/clk/Kconfig
> index 455fd17..36a6918a 100644
> --- a/drivers/clk/Kconfig
> +++ b/drivers/clk/Kconfig
> @@ -129,6 +129,13 @@ config COMMON_CLK_PALMAS
> This driver supports TI Palmas devices 32KHz output KG and KG_AUDIO
> using common clock framework.
>
> +config COMMON_CLK_PWM
> + bool "Clock driver for PWMs used as clock outputs"
> + depends on PWM
> + ---help---
> + Adapter driver so that any PWM output can be (mis)used as clock signal
> + at 50% duty cycle.
> +
> config COMMON_CLK_PXA
> def_bool COMMON_CLK && ARCH_PXA
> ---help---
> diff --git a/drivers/clk/Makefile b/drivers/clk/Makefile
> index d5fba5b..6a0c5cf 100644
> --- a/drivers/clk/Makefile
> +++ b/drivers/clk/Makefile
> @@ -40,6 +40,7 @@ obj-$(CONFIG_ARCH_U300) += clk-u300.o
> obj-$(CONFIG_ARCH_VT8500) += clk-vt8500.o
> obj-$(CONFIG_COMMON_CLK_WM831X) += clk-wm831x.o
> obj-$(CONFIG_COMMON_CLK_XGENE) += clk-xgene.o
> +obj-$(CONFIG_COMMON_CLK_PWM) += clk-pwm.o
> obj-$(CONFIG_COMMON_CLK_AT91) += at91/
> obj-$(CONFIG_ARCH_BCM_MOBILE) += bcm/
> obj-$(CONFIG_ARCH_BERLIN) += berlin/
> diff --git a/drivers/clk/clk-pwm.c b/drivers/clk/clk-pwm.c
> new file mode 100644
> index 0000000..c7d5652
> --- /dev/null
> +++ b/drivers/clk/clk-pwm.c
> @@ -0,0 +1,129 @@
> +/*
> + * Copyright (C) 2014 Philipp Zabel, Pengutronix
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * PWM (mis)used as clock output
> + */
> +#include <linux/clk-provider.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/platform_device.h>
> +#include <linux/pwm.h>
> +
> +struct clk_pwm {
> + struct clk_hw hw;
> + struct pwm_device *pwm;
> + u32 fixed_rate;
> +};
> +
> +#define to_clk_pwm(_hw) container_of(_hw, struct clk_pwm, hw)
> +
> +static int clk_pwm_prepare(struct clk_hw *hw)
> +{
> + struct clk_pwm *clk_pwm = to_clk_pwm(hw);
> +
> + return pwm_enable(clk_pwm->pwm);
> +}
> +
> +static void clk_pwm_unprepare(struct clk_hw *hw)
> +{
> + struct clk_pwm *clk_pwm = to_clk_pwm(hw);
> +
> + pwm_disable(clk_pwm->pwm);
> +}
> +
> +static unsigned long clk_pwm_recalc_rate(struct clk_hw *hw,
> + unsigned long parent_rate)
> +{
> + struct clk_pwm *clk_pwm = to_clk_pwm(hw);
> +
> + return clk_pwm->fixed_rate;
> +}
> +
> +const struct clk_ops clk_pwm_ops = {
> + .prepare = clk_pwm_prepare,
> + .unprepare = clk_pwm_unprepare,
> + .recalc_rate = clk_pwm_recalc_rate,
> +};
> +
> +int clk_pwm_probe(struct platform_device *pdev)
> +{
> + struct device_node *node = pdev->dev.of_node;
> + struct clk_init_data init;
> + struct clk_pwm *clk_pwm;
> + struct pwm_device *pwm;
> + const char *clk_name;
> + struct clk *clk;
> + int ret;
> +
> + clk_pwm = devm_kzalloc(&pdev->dev, sizeof(*clk_pwm), GFP_KERNEL);
> + if (!clk_pwm)
> + return -ENOMEM;
> +
> + pwm = devm_pwm_get(&pdev->dev, NULL);
> + if (IS_ERR(pwm))
> + return PTR_ERR(pwm);
> +
> + if (!pwm || !pwm->period) {
> + dev_err(&pdev->dev, "invalid pwm period\n");
> + return -EINVAL;
> + }
> +
> + if (of_property_read_u32(node, "clock-frequency", &clk_pwm->fixed_rate))
> + clk_pwm->fixed_rate = NSEC_PER_SEC / pwm->period;
> +
> + if (pwm->period != NSEC_PER_SEC / clk_pwm->fixed_rate &&
> + pwm->period != DIV_ROUND_UP(NSEC_PER_SEC, clk_pwm->fixed_rate)) {
> + dev_err(&pdev->dev,
> + "clock-frequency does not match pwm period\n");
> + return -EINVAL;
> + }
> +
> + ret = pwm_config(pwm, (pwm->period + 1) >> 1, pwm->period);
> + if (ret < 0)
> + return ret;
> +
> + clk_name = node->name;
> + of_property_read_string(node, "clock-output-names", &clk_name);
> +
> + init.name = clk_name;
> + init.ops = &clk_pwm_ops;
> + init.flags = CLK_IS_BASIC | CLK_IS_ROOT;
> + init.num_parents = 0;
> +
> + clk_pwm->pwm = pwm;
> + clk_pwm->hw.init = &init;
> + clk = devm_clk_register(&pdev->dev, &clk_pwm->hw);
> + if (IS_ERR(clk))
> + return PTR_ERR(clk);
> +
> + return of_clk_add_provider(node, of_clk_src_simple_get, clk);
> +}
> +
> +int clk_pwm_remove(struct platform_device *pdev)
> +{
> + of_clk_del_provider(pdev->dev.of_node);
> +
> + return 0;
> +}
> +
> +static const struct of_device_id clk_pwm_dt_ids[] = {
> + { .compatible = "pwm-clock" },
> + { }
> +};
> +MODULE_DEVICE_TABLE(of, clk_pwm_dt_ids);
> +
> +static struct platform_driver clk_pwm_driver = {
> + .probe = clk_pwm_probe,
> + .remove = clk_pwm_remove,
> + .driver = {
> + .name = "pwm-clock",
> + .of_match_table = of_match_ptr(clk_pwm_dt_ids),
> + },
> +};
> +
> +module_platform_driver(clk_pwm_driver);

rebased to 3.14.17 and then:

Tested-by: Janusz Uzycki <j.uzycki@elproma.com.pl>