[PATCH v4 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 aggregates one or more input clocks and/or one or
more GPIOs. It's 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 all input
clocks are locked and only then initialize dependent peripherals.

Signed-off-by: Vyacheslav Yurkov <uvv.mail@gmail.com>
Signed-off-by: Vyacheslav Yurkov <V.Yurkov.EXT@bruker.com>
---
 drivers/clk/Makefile          |   1 +
 drivers/clk/clk-gpio-locked.c | 306 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 307 insertions(+)

diff --git a/drivers/clk/Makefile b/drivers/clk/Makefile
index cc108a75a900..846383ed0358 100644
--- a/drivers/clk/Makefile
+++ b/drivers/clk/Makefile
@@ -35,6 +35,7 @@ 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..79098f9b6532
--- /dev/null
+++ b/drivers/clk/clk-gpio-locked.c
@@ -0,0 +1,306 @@
+// 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>
+
+#define MAX_INPUT_GPIO_COUNT 32
+
+/**
+ * struct gpio_locked_clk_priv - private state for the whole driver
+ * @dev:		platform device
+ *
+ * @clks:		array of input clock descriptors
+ * @num_clks:		number of entries in @inputs
+ *
+ * @gpios:		array of GPIO descriptors
+ * @gpio_names:		GPIO names
+ * @num_gpios:		number of input GPIOs
+ *
+ * @output_hw_clk:      output clock HW descriptor
+ * @output_clock_name:  output clock name
+ */
+struct gpio_locked_clk_priv {
+	struct device *dev;
+
+	struct clk_bulk_data *clks;
+	int num_clks;
+
+	struct gpio_descs *gpios;
+	const char **gpio_names;
+	int num_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 is_gpio_ready(struct gpio_locked_clk_priv *priv)
+{
+	unsigned long values[BITS_TO_LONGS(MAX_INPUT_GPIO_COUNT)] = {0};
+	int ret = 0;
+
+	if (priv->num_gpios == 0)
+		return 0;
+
+	ret = gpiod_get_array_value(priv->gpios->ndescs,
+		priv->gpios->desc,
+		priv->gpios->info,
+		values);
+
+	if (ret) {
+		dev_err(priv->dev, "Failed to read GPIOs");
+		return -EIO;
+	}
+
+	for (int i = 0; i < priv->gpios->ndescs; i++) {
+		if (!test_bit(i, values)) {
+			dev_warn(priv->dev, "GPIO %s is not ready", priv->gpio_names[i]);
+			return -EBUSY;
+		}
+	}
+
+	return 0;
+}
+
+static int gpio_locked_clk_is_enabled(struct clk_hw *hw)
+{
+	struct gpio_locked_clk_priv *priv = to_gpio_locked_clk_priv(hw);
+	int ret = 0;
+
+	if (priv->num_gpios > 0) {
+		ret = is_gpio_ready(priv);
+		if (ret < 0)
+			return ret;
+	}
+
+	// Now check for the clocks
+	for (int i = 0; i < priv->num_clks; i++) {
+		struct clk_hw *hw_clk = __clk_get_hw(priv->clks[i].clk);
+
+		if (!clk_hw_is_enabled(hw_clk)) {
+			dev_dbg(priv->dev, "Clock %i (%s) is not ready",
+				i, priv->clks[i].id);
+			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_inputs(struct gpio_locked_clk_priv *priv)
+{
+	struct device *dev = priv->dev;
+	int ret;
+
+	ret = devm_clk_bulk_get_all(dev, &priv->clks);
+	if (ret < 0) {
+		dev_err(dev, "failed to get input clocks: %d\n", ret);
+		return ret ? ret : -ENOENT;
+	}
+
+	priv->num_clks = ret;
+
+	if (priv->num_clks == 0)
+		dev_info(dev, "No input clocks provided\n");
+
+	for (int i = 0; i < priv->num_clks; i++)
+		dev_dbg(dev, "input clk[%d]: name='%s' rate=%lu Hz\n",
+			i, priv->clks[i].id,
+			clk_get_rate(priv->clks[i].clk));
+
+	return 0;
+}
+
+static int gpio_locked_clk_parse_gpios(struct gpio_locked_clk_priv *priv)
+{
+	struct device *dev = priv->dev;
+	struct device_node *np = dev->of_node;
+	int i;
+
+	priv->gpios = devm_gpiod_get_array_optional(dev, "locked", GPIOD_ASIS);
+	if (IS_ERR(priv->gpios)) {
+		dev_err(dev, "failed to get GPIO array: %ld\n",
+				PTR_ERR(priv->gpios));
+		return PTR_ERR(priv->gpios);
+	}
+
+	if (!priv->gpios) {
+		dev_info(dev, "No GPIOs provided, continue\n");
+		priv->num_gpios = 0;
+		return 0;
+	}
+
+	priv->num_gpios = priv->gpios->ndescs;
+	if (priv->num_gpios > MAX_INPUT_GPIO_COUNT) {
+		dev_err(priv->dev, "Maximum number of input GPIOs is 32\n");
+		return -EINVAL;
+	}
+
+	/* gpio_descs carries no names, so read "gpio-names" separately */
+	priv->gpio_names = devm_kcalloc(dev, priv->num_gpios, sizeof(*priv->gpio_names),
+			GFP_KERNEL);
+	if (!priv->gpio_names)
+		return -ENOMEM;
+
+	for (i = 0; i < priv->num_gpios; i++) {
+		of_property_read_string_index(np, "gpio-names", i,
+				&priv->gpio_names[i]);
+
+		dev_dbg(dev, "gpio[%d]: name='%s'\n",
+				i, priv->gpio_names[i] ? priv->gpio_names[i] : "(unnamed)");
+	}
+
+	return 0;
+}
+
+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;
+	struct clk_init_data init = {};
+	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);
+
+	init.name = priv->output_clock_name;
+	init.ops = &gpio_locked_clk_ops;
+	init.flags = 0;
+	init.num_parents = priv->num_clks;
+
+	if (priv->num_clks) {
+		const char **parent_names;
+		int j;
+
+		parent_names = devm_kcalloc(dev, priv->num_clks,
+					    sizeof(*parent_names),
+					    GFP_KERNEL);
+		if (!parent_names)
+			return -ENOMEM;
+
+		for (j = 0; j < priv->num_clks; j++)
+			parent_names[j] = priv->clks[j].id;
+
+		init.parent_names = parent_names;
+	}
+
+	priv->output_hw_clk.init = &init;
+
+	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);
+
+	ret = gpio_locked_clk_parse_inputs(priv);
+	if (ret)
+		return ret;
+
+	ret = gpio_locked_clk_parse_gpios(priv);
+	if (ret)
+		return ret;
+
+	if (priv->num_clks == 0 && priv->num_gpios == 0) {
+		dev_err(priv->dev, "At least 1 input clock or input GPIO is required\n");
+		return -EINVAL;
+	}
+
+	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 %u input clocks, %u GPIOs\n",
+		 priv->num_clks, priv->num_gpios);
+
+	return 0;
+}
+
+static void gpio_locked_clk_remove(struct platform_device *pdev)
+{
+	dev_dbg(&pdev->dev, "removed\n");
+}
+
+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,
+	.remove = gpio_locked_clk_remove,
+	.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