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

[Vyacheslav Yurkov via B4 Relay <devnull+V.Yurkov.EXT.bruker.com@kernel.org>]

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.

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");
+
+	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