Re: [PATCH v5 2/2] clk: Add gpio-locked fixed clock driver

[Jerome Brunet <jbrunet@baylibre.com>]

On mar. 15 sept. 2026 at 09:27, Vyacheslav Yurkov via B4 Relay <devnull+V.Yurkov.EXT.bruker.com@kernel.org> wrote:

> From: Vyacheslav Yurkov <V.Yurkov.EXT@bruker.com>
>
> A gpio-locked clock exposes a clock, which status is determined by a
> GPIO signal. The common use-case is a FPGA-assisted clocking design
> where peripheral clocks are generated by FPGA PLLs that are outside
> CPU control, with clock-valid/PLL-lock status exposed through GPIO signals.
> Consumers can use the output clock to wait until the input clock is locked
> and only then initialize dependent peripherals.
>

We already have gpio gate driver in drivers/clk/clk-gpio.c

It would be much better if you could just extend that one that take
optionally take a clock input like you do here.

> Signed-off-by: Vyacheslav Yurkov <V.Yurkov.EXT@bruker.com>
> ---
>  drivers/clk/Makefile          |   1 +
>  drivers/clk/clk-gpio-locked.c | 169 ++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 170 insertions(+)
>
> diff --git a/drivers/clk/Makefile b/drivers/clk/Makefile
> index b18af485d7f0..b904f292d683 100644
> --- a/drivers/clk/Makefile
> +++ b/drivers/clk/Makefile
> @@ -46,6 +46,7 @@ obj-$(CONFIG_CLK_FD_KUNIT_TEST) += clk-fractional-divider_test.o
>  obj-$(CONFIG_COMMON_CLK)	+= clk-gpio.o
>  ifeq ($(CONFIG_OF), y)
>  obj-$(CONFIG_COMMON_CLK)	+= clk-conf.o
> +obj-$(CONFIG_COMMON_CLK)	+= clk-gpio-locked.o
>  endif
>  
>  # KUnit specific helpers
> diff --git a/drivers/clk/clk-gpio-locked.c b/drivers/clk/clk-gpio-locked.c
> new file mode 100644
> index 000000000000..b648f8763922
> --- /dev/null
> +++ b/drivers/clk/clk-gpio-locked.c
> @@ -0,0 +1,169 @@
> +// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +/*
> + * Clock Controller Guard Driver
> + *
> + * Copyright 2026 Bruker Corporation
> + */
> +
> +#include <linux/clk.h>
> +#include <linux/clk-provider.h>
> +#include <linux/device.h>
> +#include <linux/gpio/consumer.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/platform_device.h>
> +#include <linux/slab.h>
> +
> +/**
> + * struct gpio_locked_clk_priv - private state for the whole driver
> + * @dev:		platform device
> + *
> + * @input_clk	input clock
> + * @gpios:		input GPIO descriptor
> + *
> + * @output_hw_clk:      output clock HW descriptor
> + * @output_clock_name:  output clock name
> + */
> +struct gpio_locked_clk_priv {
> +	struct device *dev;
> +
> +	struct clk *input_clk;
> +	struct gpio_desc *gpios;
> +
> +	struct clk_hw output_hw_clk;
> +	const char *output_clock_name;
> +};
> +
> +#define to_gpio_locked_clk_priv(_hw) \
> +	container_of(_hw, struct gpio_locked_clk_priv, output_hw_clk)
> +
> +static int gpio_locked_clk_is_enabled(struct clk_hw *hw)
> +{
> +	struct gpio_locked_clk_priv *priv = to_gpio_locked_clk_priv(hw);
> +
> +	int data = gpiod_get_value(priv->gpios);
> +
> +	if (data < 0) {
> +		dev_err(priv->dev, "Failed to get data gpio val: %d\n",
> +				data);
> +		return data;
> +	} else if (!data) {
> +		dev_warn(priv->dev, "GPIO is not ready");
> +		return -EBUSY;
> +	}
> +
> +	return 0;
> +}
> +
> +/* We can't enable the clock, but the Common Clock Framework calls only
> + * enable() not is_enabled()
> + */
> +static int gpio_locked_clk_enable(struct clk_hw *hw)
> +{
> +	return gpio_locked_clk_is_enabled(hw);
> +}
> +
> +/* We have to implement it, but we are not going to control
> + * parent clock selection
> + */
> +static u8 gpio_locked_clk_get_parent(struct clk_hw *hw)
> +{
> +	return 0;
> +}
> +
> +static const struct clk_ops gpio_locked_clk_ops = {
> +	.enable =	gpio_locked_clk_enable,
> +	.is_enabled =	gpio_locked_clk_is_enabled,
> +	.get_parent =	gpio_locked_clk_get_parent,
> +};
> +
> +static int gpio_locked_clk_parse_outputs(struct gpio_locked_clk_priv *priv)
> +{
> +	struct device *dev = priv->dev;
> +	struct device_node *np = dev->of_node;
> +	int ret;
> +
> +	of_property_read_string_index(np, "clock-output-names", 0,
> +		&priv->output_clock_name);
> +
> +	if (!priv->output_clock_name)
> +		priv->output_clock_name = dev_name(priv->dev);
> +
> +	priv->output_hw_clk.init =
> +		CLK_HW_INIT_FW_NAME(priv->output_clock_name,
> +				    __clk_get_name(priv->input_clk),
> +				    &gpio_locked_clk_ops, 0);
> +
> +	ret = devm_clk_hw_register(dev, &priv->output_hw_clk);
> +	if (ret) {
> +		dev_err(dev, "failed to register output clk'%s': %d\n",
> +			priv->output_clock_name, ret);
> +		return ret;
> +	}
> +
> +	dev_info(priv->dev, "Output clock '%s' registered\n", priv->output_clock_name);
> +
> +	return 0;
> +}
> +
> +static int gpio_locked_clk_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct gpio_locked_clk_priv *priv;
> +	int ret;
> +
> +	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
> +	if (!priv)
> +		return -ENOMEM;
> +
> +	priv->dev = dev;
> +	platform_set_drvdata(pdev, priv);
> +
> +	priv->input_clk = devm_clk_get_enabled(priv->dev, NULL);
> +	if (IS_ERR(priv->input_clk))
> +		return dev_err_probe(priv->dev, PTR_ERR(priv->input_clk),
> +				"Failed to get locked fixed clock, not yet ready\n");

In your use case it might be fixed, but nothing says it is in general

> +
> +	priv->gpios = devm_gpiod_get(priv->dev, "locked", GPIOD_ASIS);
> +	if (IS_ERR(priv->gpios)) {
> +		dev_err(dev, "failed to get locked gpios: %ld\n",
> +				PTR_ERR(priv->gpios));
> +		return PTR_ERR(priv->gpios);
> +	}
> +
> +	ret = gpio_locked_clk_parse_outputs(priv);
> +	if (ret)
> +		return ret;
> +
> +	ret = devm_of_clk_add_hw_provider(priv->dev, of_clk_hw_simple_get,
> +		&priv->output_hw_clk);
> +	if (ret) {
> +		dev_err(priv->dev, "failed to register clock provider '%s': %d\n",
> +			priv->output_clock_name, ret);
> +		return ret;
> +	}
> +
> +	dev_info(dev, "registered %s gpio locked clock\n",
> +		 clk_hw_get_name(&priv->output_hw_clk));
> +
> +	return 0;
> +}
> +
> +static const struct of_device_id gpio_locked_clk_of_match[] = {
> +	{ .compatible = "gpio-locked-fixed-clock" },
> +	{ /* sentinel */ }
> +};
> +MODULE_DEVICE_TABLE(of, gpio_locked_clk_of_match);
> +
> +static struct platform_driver gpio_locked_clk_driver = {
> +	.probe  = gpio_locked_clk_probe,
> +	.driver = {
> +		.name           = "gpio-locked-fixed-clock",
> +		.of_match_table = gpio_locked_clk_of_match,
> +	},
> +};
> +module_platform_driver(gpio_locked_clk_driver);
> +
> +MODULE_AUTHOR("Vyacheslav Yurkov <V.Yurkov.EXT@bruker.com>");
> +MODULE_DESCRIPTION("GPIO-locked clock driver");
> +MODULE_LICENSE("Dual BSD/GPL");
>
> -- 
> 2.34.1
>
>

pw-bot: changes-requested

-- 
Jerome