[PATCH v8 0/2] A proposal to add a gpio-locked clock driver.

[PATCH v8 0/2] A proposal to add a gpio-locked clock driver.

[Vyacheslav Yurkov via B4 Relay]

A gpio-locked clock represents an input clock, which state is determined
by a GPIO signal. It's similar to a gated-fixed-clock, but GPIO direction
is inverted. Consumers can use the output clock to wait until all input
clocks are locked and only then initialize / access dependent peripherals.

The usage example for such a driver is when peripherals depend on PLLs in
a FPGA, which can't be directly accessed by the CPU, but need a GPIO pin
to check whether clock is actually usable. E.g. some of the IPs might not
have a proper split between registers and IP core, which means that if an
external clock and/or PLL lock is missing and one tries to access the 
registers, the response never comes, thus the CPU stalls.

Signed-off-by: Vyacheslav Yurkov <uvv.mail@gmail.com>
Signed-off-by: Vyacheslav Yurkov <V.Yurkov.EXT@bruker.com>
---
Changes in v8:
- Fix return value of clk_gpio_locked_prepare()
- Link to v7: https://lore.kernel.org/r/20260927-feature-clock-guard-v7-0-8dd19568d9a2@bruker.com

Changes in v7:
- Fix compatibility strings and schema errors.
- Update GPIO pin name
- Link to v6: https://lore.kernel.org/r/20260927-feature-clock-guard-v6-0-007983b13ec2@bruker.com

Changes in v6:
- Debug messages dropped.
- The new driver is now an extension of exising clk-gpio drivers.
- The controller doesn't enable the parent clock, the consumer is
  supposed to do that instead.
- Link to v5: https://lore.kernel.org/r/20260915-feature-clock-guard-v5-0-42ab5dc3a6aa@bruker.com

Changes in v5:
- Use existing DT binding with an additional property instead of adding
  a new one
- The driver is simplified in a way that it represents the actual HW
  desgin without additional unrelated constructs
- Aggregation is removed, now it's one clock input, one clock output
- Link to v4: https://lore.kernel.org/r/20260726-feature-clock-guard-v4-0-e9c8b372b71c@bruker.com

Changes in v4:
- Removed driver specifics from DT binding
- Link to v3: https://lore.kernel.org/r/20260603-feature-clock-guard-v3-0-01cca0aa04a5@bruker.com

Changes in v3:
- Removed unnecessary dt bindings
- Improved HW description and commit messages
- Link to v2: https://lore.kernel.org/r/20260510-feature-clock-guard-v2-0-6c25458d5340@bruker.com

Changes in v2:
- Renamed to clk-gpio-locked to express intent.
- Provide enable() / is_enabled() operations so the clock behaves as
  expected
- Fixed DTS errors / warnings
- Link to v1: https://lore.kernel.org/r/20260318-feature-clock-guard-v1-0-6137cb4084b7@bruker.com

---
Vyacheslav Yurkov (2):
      dt-bindings: clock: gpio-gate-clock: Add a new compatible string
      clk: Add gpio-locked clock driver

 .../devicetree/bindings/clock/gpio-gate-clock.yaml | 32 +++++++++++++-
 drivers/clk/clk-gpio.c                             | 50 ++++++++++++++++++++--
 2 files changed, 77 insertions(+), 5 deletions(-)
---
base-commit: fd179f8a05be3ccae366b9b96e176b51fbe54aab
change-id: 20260318-feature-clock-guard-f20a2c35b965

Best regards,
-- 
Vyacheslav Yurkov <V.Yurkov.EXT@bruker.com>

[PATCH v8 1/2] dt-bindings: clock: gpio-gate-clock: Add a new compatible string

[Vyacheslav Yurkov via B4 Relay]

From: Vyacheslav Yurkov <V.Yurkov.EXT@bruker.com>

Extend the binding to be used also for gpio-locked-fixed-clock.
A GPIO-locked fixed clock provider exposes a fixed-rate clock whose
availability depends on one or more GPIO lock-status signals.

Some hardware designs provide fixed-frequency clocks generated outside
software control, such as by FPGA-resident PLLs. While the clock rate is
fixed, a separate GPIO signal indicates whether the clock source is
locked and producing a valid output.

Signed-off-by: Vyacheslav Yurkov <V.Yurkov.EXT@bruker.com>
---
 .../devicetree/bindings/clock/gpio-gate-clock.yaml | 32 ++++++++++++++++++++--
 1 file changed, 30 insertions(+), 2 deletions(-)

diff --git a/Documentation/devicetree/bindings/clock/gpio-gate-clock.yaml b/Documentation/devicetree/bindings/clock/gpio-gate-clock.yaml
index d09d0e3f0c6e..1ad87c8b36b9 100644
--- a/Documentation/devicetree/bindings/clock/gpio-gate-clock.yaml
+++ b/Documentation/devicetree/bindings/clock/gpio-gate-clock.yaml
@@ -11,7 +11,9 @@ maintainers:
 
 properties:
   compatible:
-    const: gpio-gate-clock
+    enum:
+      - gpio-gate-clock
+      - gpio-locked-clock
 
   clocks:
     maxItems: 1
@@ -23,10 +25,29 @@ properties:
     description: GPIO reference for enabling and disabling the clock.
     maxItems: 1
 
+  enabled-gpios:
+    description: GPIO that indicates whether the clock is enabled or disabled.
+    maxItems: 1
+
 required:
   - compatible
   - '#clock-cells'
-  - enable-gpios
+
+allOf:
+  - if:
+      properties:
+        compatible:
+          const: gpio-gate-clock
+    then:
+      required:
+        - enable-gpios
+  - if:
+      properties:
+        compatible:
+          const: gpio-locked-clock
+    then:
+      required:
+        - enabled-gpios
 
 additionalProperties: false
 
@@ -40,3 +61,10 @@ examples:
         #clock-cells = <0>;
         enable-gpios = <&gpio 1 GPIO_ACTIVE_HIGH>;
     };
+
+    clk_gpio_locked {
+        compatible = "gpio-locked-clock";
+        #clock-cells = <0>;
+        clocks = <&pll>;
+        enabled-gpios = <&gpio0 4 GPIO_ACTIVE_HIGH>;
+    };

-- 
2.34.1

Re: [PATCH v8 1/2] dt-bindings: clock: gpio-gate-clock: Add a new compatible string

[Jerome Brunet]

On Sun 27 Sep 2026 at 14:59, Vyacheslav Yurkov via B4 Relay <devnull+V.Yurkov.EXT.bruker.com@kernel.org> wrote:

> From: Vyacheslav Yurkov <V.Yurkov.EXT@bruker.com>
>
> Extend the binding to be used also for gpio-locked-fixed-clock.
> A GPIO-locked fixed clock provider exposes a fixed-rate clock whose
> availability depends on one or more GPIO lock-status signals.
>
> Some hardware designs provide fixed-frequency clocks generated outside
> software control, such as by FPGA-resident PLLs. While the clock rate is
> fixed, a separate GPIO signal indicates whether the clock source is
> locked and producing a valid output.
>
> Signed-off-by: Vyacheslav Yurkov <V.Yurkov.EXT@bruker.com>
> ---
>  .../devicetree/bindings/clock/gpio-gate-clock.yaml | 32 ++++++++++++++++++++--
>  1 file changed, 30 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/devicetree/bindings/clock/gpio-gate-clock.yaml b/Documentation/devicetree/bindings/clock/gpio-gate-clock.yaml
> index d09d0e3f0c6e..1ad87c8b36b9 100644
> --- a/Documentation/devicetree/bindings/clock/gpio-gate-clock.yaml
> +++ b/Documentation/devicetree/bindings/clock/gpio-gate-clock.yaml
> @@ -11,7 +11,9 @@ maintainers:
>  
>  properties:
>    compatible:
> -    const: gpio-gate-clock
> +    enum:
> +      - gpio-gate-clock
> +      - gpio-locked-clock

I think this name does not illustrate well what your driver does
anymore. As I noted before, locked if very much PLL centric. enabled ?

While the driver sits in the same C file (clk-gpio), I don't the binding doc
should. I'll defer to the DT folks on this but I think it would more
approriate with a different yaml. clk-gpio-gate and clk-gpio-mux have
their own binding doc

>  
>    clocks:
>      maxItems: 1
> @@ -23,10 +25,29 @@ properties:
>      description: GPIO reference for enabling and disabling the clock.
>      maxItems: 1
>  
> +  enabled-gpios:
> +    description: GPIO that indicates whether the clock is enabled or disabled.
> +    maxItems: 1
> +
>  required:
>    - compatible
>    - '#clock-cells'
> -  - enable-gpios
> +
> +allOf:
> +  - if:
> +      properties:
> +        compatible:
> +          const: gpio-gate-clock
> +    then:
> +      required:
> +        - enable-gpios
> +  - if:
> +      properties:
> +        compatible:
> +          const: gpio-locked-clock

I think there should be a property in here to express how long you are
willing to wait for the clock to be enabled. IOW the lock timeout.

> +    then:
> +      required:
> +        - enabled-gpios
>  
>  additionalProperties: false
>  
> @@ -40,3 +61,10 @@ examples:
>          #clock-cells = <0>;
>          enable-gpios = <&gpio 1 GPIO_ACTIVE_HIGH>;
>      };
> +
> +    clk_gpio_locked {
> +        compatible = "gpio-locked-clock";
> +        #clock-cells = <0>;
> +        clocks = <&pll>;
> +        enabled-gpios = <&gpio0 4 GPIO_ACTIVE_HIGH>;
> +    };
>
> -- 
> 2.34.1
>
>

-- 
Jerome

[PATCH v8 2/2] clk: Add gpio-locked clock driver

[Vyacheslav Yurkov via B4 Relay]

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/clk-gpio.c | 50 +++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 47 insertions(+), 3 deletions(-)

diff --git a/drivers/clk/clk-gpio.c b/drivers/clk/clk-gpio.c
index 9099c57e2715..db68b8bc44c5 100644
--- a/drivers/clk/clk-gpio.c
+++ b/drivers/clk/clk-gpio.c
@@ -138,6 +138,25 @@ static const struct clk_ops clk_gpio_mux_ops = {
 	.determine_rate = __clk_mux_determine_rate,
 };
 
+/* We can't prepare the clock, but the Common Clock Framework calls only
+ * prepare() not is_prepared(), therefore we fallback on the actuall GPIO value.
+ * The function clk_sleeping_gpio_gate_is_prepared() returns the raw boolean
+ * GPIO status (1 if locked, 0 if unlocked), but the prepare callback
+ * clk_core_prepare() expects 0 for success and non-zero integer for failure.
+ */
+static int clk_gpio_locked_prepare(struct clk_hw *hw)
+{
+	if (clk_sleeping_gpio_gate_is_prepared(hw))
+		return 0;
+
+	return -EBUSY;
+}
+
+static const struct clk_ops clk_gpio_locked_ops = {
+	.prepare =	clk_gpio_locked_prepare,
+	.is_prepared =	clk_sleeping_gpio_gate_is_prepared,
+};
+
 static struct clk_hw *clk_register_gpio(struct device *dev, u8 num_parents,
 					struct gpio_desc *gpiod,
 					const struct clk_ops *clk_gpio_ops)
@@ -146,6 +165,7 @@ static struct clk_hw *clk_register_gpio(struct device *dev, u8 num_parents,
 	struct clk_hw *hw;
 	struct clk_init_data init = {};
 	int err;
+	const char *clk_name;
 	const struct clk_parent_data gpio_parent_data[] = {
 		{ .index = 0 },
 		{ .index = 1 },
@@ -155,7 +175,11 @@ static struct clk_hw *clk_register_gpio(struct device *dev, u8 num_parents,
 	if (!clk_gpio)
 		return ERR_PTR(-ENOMEM);
 
-	init.name = dev->of_node->name;
+	err = device_property_read_string(dev, "clock-output-names", &clk_name);
+	if (err)
+		clk_name = fwnode_get_name(dev->fwnode);
+
+	init.name = clk_name;
 	init.ops = clk_gpio_ops;
 	init.parent_data = gpio_parent_data;
 	init.num_parents = num_parents;
@@ -192,6 +216,12 @@ static struct clk_hw *clk_hw_register_gpio_mux(struct device *dev,
 	return clk_register_gpio(dev, 2, gpiod, &clk_gpio_mux_ops);
 }
 
+static struct clk_hw *clk_hw_register_gpio_locked(struct device *dev,
+						  struct gpio_desc *gpiod)
+{
+	return clk_register_gpio(dev, 1, gpiod, &clk_gpio_locked_ops);
+}
+
 static int gpio_clk_driver_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
@@ -201,8 +231,11 @@ static int gpio_clk_driver_probe(struct platform_device *pdev)
 	struct gpio_desc *gpiod;
 	struct clk_hw *hw;
 	bool is_mux;
+	bool is_gpio_locked;
+	enum gpiod_flags gpio_flags;
 
 	is_mux = of_device_is_compatible(node, "gpio-mux-clock");
+	is_gpio_locked = of_device_is_compatible(node, "gpio-locked-clock");
 
 	num_parents = of_clk_get_parent_count(node);
 	if (is_mux && num_parents != 2) {
@@ -210,14 +243,24 @@ static int gpio_clk_driver_probe(struct platform_device *pdev)
 		return -EINVAL;
 	}
 
-	gpio_name = is_mux ? "select" : "enable";
-	gpiod = devm_gpiod_get(dev, gpio_name, GPIOD_OUT_LOW);
+	if (is_mux)
+		gpio_name = "select";
+	else if (is_gpio_locked)
+		gpio_name = "enabled";
+	else
+		gpio_name = "enable";
+
+	gpio_flags = is_gpio_locked ? GPIOD_IN : GPIOD_OUT_LOW;
+
+	gpiod = devm_gpiod_get(dev, gpio_name, gpio_flags);
 	if (IS_ERR(gpiod))
 		return dev_err_probe(dev, PTR_ERR(gpiod),
 				     "Can't get '%s' named GPIO property\n", gpio_name);
 
 	if (is_mux)
 		hw = clk_hw_register_gpio_mux(dev, gpiod);
+	else if (is_gpio_locked)
+		hw = clk_hw_register_gpio_locked(dev, gpiod);
 	else
 		hw = clk_hw_register_gpio_gate(dev, num_parents, gpiod);
 	if (IS_ERR(hw))
@@ -229,6 +272,7 @@ static int gpio_clk_driver_probe(struct platform_device *pdev)
 static const struct of_device_id gpio_clk_match_table[] = {
 	{ .compatible = "gpio-mux-clock" },
 	{ .compatible = "gpio-gate-clock" },
+	{ .compatible = "gpio-locked-clock" },
 	{ }
 };
 

-- 
2.34.1

Re: [PATCH v8 2/2] clk: Add gpio-locked clock driver

[Jerome Brunet]

On Sun 27 Sep 2026 at 14:59, 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.
>
> Signed-off-by: Vyacheslav Yurkov <V.Yurkov.EXT@bruker.com>
> ---
>  drivers/clk/clk-gpio.c | 50 +++++++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 47 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/clk/clk-gpio.c b/drivers/clk/clk-gpio.c
> index 9099c57e2715..db68b8bc44c5 100644
> --- a/drivers/clk/clk-gpio.c
> +++ b/drivers/clk/clk-gpio.c
> @@ -138,6 +138,25 @@ static const struct clk_ops clk_gpio_mux_ops = {
>  	.determine_rate = __clk_mux_determine_rate,
>  };
>  
> +/* We can't prepare the clock, but the Common Clock Framework calls only
> + * prepare() not is_prepared(), therefore we fallback on the actuall GPIO value.
> + * The function clk_sleeping_gpio_gate_is_prepared() returns the raw boolean
> + * GPIO status (1 if locked, 0 if unlocked), but the prepare callback
> + * clk_core_prepare() expects 0 for success and non-zero integer for failure.
> + */
> +static int clk_gpio_locked_prepare(struct clk_hw *hw)
> +{
> +	if (clk_sleeping_gpio_gate_is_prepared(hw))
> +		return 0;
> +
> +	return -EBUSY;
> +}

I was apparently not clear - probably my fault since I was initially
confused with what the driver was supposed to do.

Please do not modify the gate driver. Just provide gpio-enabled-clock
clock driver along the gate and mux in there.

> +
> +static const struct clk_ops clk_gpio_locked_ops = {
> +	.prepare =	clk_gpio_locked_prepare,
> +	.is_prepared =	clk_sleeping_gpio_gate_is_prepared,
> +};

Please implement the ops you've be testing, fast or slow (or both :D if
you can test both) 

> +
>  static struct clk_hw *clk_register_gpio(struct device *dev, u8 num_parents,
>  					struct gpio_desc *gpiod,
>  					const struct clk_ops *clk_gpio_ops)
> @@ -146,6 +165,7 @@ static struct clk_hw *clk_register_gpio(struct device *dev, u8 num_parents,
>  	struct clk_hw *hw;
>  	struct clk_init_data init = {};
>  	int err;
> +	const char *clk_name;
>  	const struct clk_parent_data gpio_parent_data[] = {
>  		{ .index = 0 },
>  		{ .index = 1 },
> @@ -155,7 +175,11 @@ static struct clk_hw *clk_register_gpio(struct device *dev, u8 num_parents,
>  	if (!clk_gpio)
>  		return ERR_PTR(-ENOMEM);
>  
> -	init.name = dev->of_node->name;
> +	err = device_property_read_string(dev, "clock-output-names", &clk_name);
> +	if (err)
> +		clk_name = fwnode_get_name(dev->fwnode);
> +
> +	init.name = clk_name;
>  	init.ops = clk_gpio_ops;
>  	init.parent_data = gpio_parent_data;
>  	init.num_parents = num_parents;
> @@ -192,6 +216,12 @@ static struct clk_hw *clk_hw_register_gpio_mux(struct device *dev,
>  	return clk_register_gpio(dev, 2, gpiod, &clk_gpio_mux_ops);
>  }
>  
> +static struct clk_hw *clk_hw_register_gpio_locked(struct device *dev,
> +						  struct gpio_desc *gpiod)
> +{
> +	return clk_register_gpio(dev, 1, gpiod, &clk_gpio_locked_ops);
> +}
> +
>  static int gpio_clk_driver_probe(struct platform_device *pdev)
>  {
>  	struct device *dev = &pdev->dev;
> @@ -201,8 +231,11 @@ static int gpio_clk_driver_probe(struct platform_device *pdev)
>  	struct gpio_desc *gpiod;
>  	struct clk_hw *hw;
>  	bool is_mux;
> +	bool is_gpio_locked;
> +	enum gpiod_flags gpio_flags;
>  
>  	is_mux = of_device_is_compatible(node, "gpio-mux-clock");
> +	is_gpio_locked = of_device_is_compatible(node, "gpio-locked-clock");
>  
>  	num_parents = of_clk_get_parent_count(node);
>  	if (is_mux && num_parents != 2) {
> @@ -210,14 +243,24 @@ static int gpio_clk_driver_probe(struct platform_device *pdev)
>  		return -EINVAL;
>  	}
>  
> -	gpio_name = is_mux ? "select" : "enable";
> -	gpiod = devm_gpiod_get(dev, gpio_name, GPIOD_OUT_LOW);
> +	if (is_mux)
> +		gpio_name = "select";
> +	else if (is_gpio_locked)
> +		gpio_name = "enabled";
> +	else
> +		gpio_name = "enable";
> +
> +	gpio_flags = is_gpio_locked ? GPIOD_IN : GPIOD_OUT_LOW;
> +
> +	gpiod = devm_gpiod_get(dev, gpio_name, gpio_flags);
>  	if (IS_ERR(gpiod))
>  		return dev_err_probe(dev, PTR_ERR(gpiod),
>  				     "Can't get '%s' named GPIO property\n", gpio_name);
>  
>  	if (is_mux)
>  		hw = clk_hw_register_gpio_mux(dev, gpiod);
> +	else if (is_gpio_locked)
> +		hw = clk_hw_register_gpio_locked(dev, gpiod);
>  	else
>  		hw = clk_hw_register_gpio_gate(dev, num_parents, gpiod);
>  	if (IS_ERR(hw))
> @@ -229,6 +272,7 @@ static int gpio_clk_driver_probe(struct platform_device *pdev)
>  static const struct of_device_id gpio_clk_match_table[] = {
>  	{ .compatible = "gpio-mux-clock" },
>  	{ .compatible = "gpio-gate-clock" },
> +	{ .compatible = "gpio-locked-clock" },
>  	{ }
>  };
>  
>
> -- 
> 2.34.1
>
>

-- 
Jerome