[PATCH v2] ACPI: platform: Add basic support for ACPI 6.5 fixed clock resources

[PATCH v2] ACPI: platform: Add basic support for ACPI 6.5 fixed clock resources

[Paul Cercueil]

ACPI 6.5 introduced a clock input resource descriptor, which allows to
specify in the ACPI tables what clocks are connected to a given device.

This patch adds support for the most basic clock resource, which is the
one that represents a fixed clock. The new code will then create a
clk_hw for each fixed clock resource, which is then made available to
the device drivers, that can obtain it through a regular call to
clk_get(NULL).

Signed-off-by: Paul Cercueil <paul.cercueil@bootlin.com>

---

Related:
https://lore.kernel.org/linux-arm-kernel/20261103084915.8405-1-paul.cercueil@bootlin.com/T/

v2:
- Use the calculated clock name in devm_clk_hw_register_fixed_rate()
  instead of the device name
- Make sure clkres->scale is <= 2. The field is 2 bits but the value
  clkres->scale == 3 is not defined in the spec.
- Compute the fraction numerator using 64-bit math, to make sure it
  won't overflow on 32-bit systems.
- Initialize clocks only when the device_type matches
  ACPI_BUS_TYPE_DEVICE.
- Use a shorter name for clocks as the hard limit is 16 characters
  including the terminator.
---
 drivers/acpi/acpi_platform.c | 64 ++++++++++++++++++++++++++++++++++++
 1 file changed, 64 insertions(+)

diff --git a/drivers/acpi/acpi_platform.c b/drivers/acpi/acpi_platform.c
index 80ea7121744d..71322cdcf0dd 100644
--- a/drivers/acpi/acpi_platform.c
+++ b/drivers/acpi/acpi_platform.c
@@ -10,17 +10,27 @@
 
 #include <linux/acpi.h>
 #include <linux/bits.h>
+#include <linux/clk-provider.h>
+#include <linux/clkdev.h>
 #include <linux/device.h>
 #include <linux/err.h>
 #include <linux/ioport.h>
+#include <linux/kconfig.h>
 #include <linux/kernel.h>
+#include <linux/list.h>
 #include <linux/module.h>
 #include <linux/dma-mapping.h>
 #include <linux/pci.h>
 #include <linux/platform_device.h>
+#include <linux/units.h>
 
 #include "internal.h"
 
+struct acpi_clk_data {
+	struct device *dev;
+	unsigned int idx;
+};
+
 /* Exclude devices that have no _CRS resources provided */
 #define ACPI_ALLOW_WO_RESOURCES		BIT(0)
 
@@ -130,6 +140,57 @@ static unsigned int acpi_platform_resource_count(struct acpi_resource *ares, voi
 	return AE_CTRL_TERMINATE;
 }
 
+static int acpi_add_fixed_clock(struct acpi_resource *res, void *d)
+{
+	static const unsigned long clk_scale[] = { 1, HZ_PER_KHZ, HZ_PER_MHZ };
+	struct acpi_resource_clock_input *clkres;
+	struct acpi_clk_data *data = d;
+	struct device *dev = data->dev;
+	struct clk_hw *clk;
+	unsigned long rate;
+	char name[64];
+	int err;
+
+	if (res->type == ACPI_RESOURCE_TYPE_CLOCK_INPUT) {
+		clkres = &res->data.clock_input;
+
+		if (clkres->mode) {
+			dev_warn(dev, "Only fixed rate clocks supported for now.\n");
+			return 1; /* keep going */
+		}
+
+		if (clkres->frequency_divisor == 0 || clkres->scale > 2)
+			return -EINVAL;
+
+		rate = DIV_ROUND_UP_ULL((u64)clkres->frequency_numerator * clk_scale[clkres->scale],
+					clkres->frequency_divisor);
+
+		snprintf(name, sizeof(name), "%s-%u", dev_name(dev), data->idx++);
+
+		clk = devm_clk_hw_register_fixed_rate(dev, name, NULL, 0, rate);
+		if (IS_ERR(clk))
+			return PTR_ERR(clk);
+
+		err = devm_clk_hw_register_clkdev(dev, clk, name, dev_name(dev));
+		if (err)
+			return err;
+	}
+
+	return 1;
+}
+
+static void acpi_platform_init_clocks(struct acpi_device *adev)
+{
+	struct device *dev = &adev->dev;
+	struct acpi_clk_data data = { .dev = dev };
+	LIST_HEAD(list);
+	int ret;
+
+	ret = acpi_dev_get_resources(adev, &list, acpi_add_fixed_clock, &data);
+	if (ret < 0)
+		dev_err(dev, "Failed to add clock resources: %d\n", ret);
+}
+
 /**
  * acpi_create_platform_device - Create platform device for ACPI device node
  * @adev: ACPI device node to create a platform device for.
@@ -196,6 +257,9 @@ struct platform_device *acpi_create_platform_device(struct acpi_device *adev,
 			}
 			acpi_dev_free_resource_list(&resource_list);
 		}
+
+		if (IS_ENABLED(CONFIG_COMMON_CLK))
+			acpi_platform_init_clocks(adev);
 	}
 
 	memset(&pdevinfo, 0, sizeof(pdevinfo));
-- 
2.47.3

Re: [PATCH v2] ACPI: platform: Add basic support for ACPI 6.5 fixed clock resources

[Paul Cercueil]

Hi Rafael,

I see Sashiko complains about this patch:
https://sashiko.dev/#/patchset/20261111100736.98364-1-paul.cercueil%40bootlin.com

But its only complaint is addressed by a second patch that was sent in parallel:
https://lore.kernel.org/linux-arm-kernel/20261103084915.8405-1-paul.cercueil@bootlin.com/T/

In retrospective I probably should have packed both into one patchset; I thought
they were parallelizable enough to go each its own way, but that was without
thinking about Sashiko.

Cheers,
-Paul

Le mercredi 11 novembre 2026 à 11:07 +0100, Paul Cercueil a écrit :
> ACPI 6.5 introduced a clock input resource descriptor, which allows to
> specify in the ACPI tables what clocks are connected to a given device.
> 
> This patch adds support for the most basic clock resource, which is the
> one that represents a fixed clock. The new code will then create a
> clk_hw for each fixed clock resource, which is then made available to
> the device drivers, that can obtain it through a regular call to
> clk_get(NULL).
> 
> Signed-off-by: Paul Cercueil <paul.cercueil@bootlin.com>
> 
> ---
> 
> Related:
> https://lore.kernel.org/linux-arm-kernel/20261103084915.8405-1-paul.cercueil@bootlin.com/T/
> 
> v2:
> - Use the calculated clock name in devm_clk_hw_register_fixed_rate()
>   instead of the device name
> - Make sure clkres->scale is <= 2. The field is 2 bits but the value
>   clkres->scale == 3 is not defined in the spec.
> - Compute the fraction numerator using 64-bit math, to make sure it
>   won't overflow on 32-bit systems.
> - Initialize clocks only when the device_type matches
>   ACPI_BUS_TYPE_DEVICE.
> - Use a shorter name for clocks as the hard limit is 16 characters
>   including the terminator.
> ---
>  drivers/acpi/acpi_platform.c | 64 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 64 insertions(+)
> 
> diff --git a/drivers/acpi/acpi_platform.c b/drivers/acpi/acpi_platform.c
> index 80ea7121744d..71322cdcf0dd 100644
> --- a/drivers/acpi/acpi_platform.c
> +++ b/drivers/acpi/acpi_platform.c
> @@ -10,17 +10,27 @@
>  
>  #include <linux/acpi.h>
>  #include <linux/bits.h>
> +#include <linux/clk-provider.h>
> +#include <linux/clkdev.h>
>  #include <linux/device.h>
>  #include <linux/err.h>
>  #include <linux/ioport.h>
> +#include <linux/kconfig.h>
>  #include <linux/kernel.h>
> +#include <linux/list.h>
>  #include <linux/module.h>
>  #include <linux/dma-mapping.h>
>  #include <linux/pci.h>
>  #include <linux/platform_device.h>
> +#include <linux/units.h>
>  
>  #include "internal.h"
>  
> +struct acpi_clk_data {
> +	struct device *dev;
> +	unsigned int idx;
> +};
> +
>  /* Exclude devices that have no _CRS resources provided */
>  #define ACPI_ALLOW_WO_RESOURCES		BIT(0)
>  
> @@ -130,6 +140,57 @@ static unsigned int acpi_platform_resource_count(struct
> acpi_resource *ares, voi
>  	return AE_CTRL_TERMINATE;
>  }
>  
> +static int acpi_add_fixed_clock(struct acpi_resource *res, void *d)
> +{
> +	static const unsigned long clk_scale[] = { 1, HZ_PER_KHZ, HZ_PER_MHZ
> };
> +	struct acpi_resource_clock_input *clkres;
> +	struct acpi_clk_data *data = d;
> +	struct device *dev = data->dev;
> +	struct clk_hw *clk;
> +	unsigned long rate;
> +	char name[64];
> +	int err;
> +
> +	if (res->type == ACPI_RESOURCE_TYPE_CLOCK_INPUT) {
> +		clkres = &res->data.clock_input;
> +
> +		if (clkres->mode) {
> +			dev_warn(dev, "Only fixed rate clocks supported for
> now.\n");
> +			return 1; /* keep going */
> +		}
> +
> +		if (clkres->frequency_divisor == 0 || clkres->scale > 2)
> +			return -EINVAL;
> +
> +		rate = DIV_ROUND_UP_ULL((u64)clkres->frequency_numerator *
> clk_scale[clkres->scale],
> +					clkres->frequency_divisor);
> +
> +		snprintf(name, sizeof(name), "%s-%u", dev_name(dev), data-
> >idx++);
> +
> +		clk = devm_clk_hw_register_fixed_rate(dev, name, NULL, 0,
> rate);
> +		if (IS_ERR(clk))
> +			return PTR_ERR(clk);
> +
> +		err = devm_clk_hw_register_clkdev(dev, clk, name,
> dev_name(dev));
> +		if (err)
> +			return err;
> +	}
> +
> +	return 1;
> +}
> +
> +static void acpi_platform_init_clocks(struct acpi_device *adev)
> +{
> +	struct device *dev = &adev->dev;
> +	struct acpi_clk_data data = { .dev = dev };
> +	LIST_HEAD(list);
> +	int ret;
> +
> +	ret = acpi_dev_get_resources(adev, &list, acpi_add_fixed_clock,
> &data);
> +	if (ret < 0)
> +		dev_err(dev, "Failed to add clock resources: %d\n", ret);
> +}
> +
>  /**
>   * acpi_create_platform_device - Create platform device for ACPI device node
>   * @adev: ACPI device node to create a platform device for.
> @@ -196,6 +257,9 @@ struct platform_device *acpi_create_platform_device(struct
> acpi_device *adev,
>  			}
>  			acpi_dev_free_resource_list(&resource_list);
>  		}
> +
> +		if (IS_ENABLED(CONFIG_COMMON_CLK))
> +			acpi_platform_init_clocks(adev);
>  	}
>  
>  	memset(&pdevinfo, 0, sizeof(pdevinfo));