[RFC,v1] media: v4l2-common: Add a helper for obtaining the clock producer

Introduce a helper for v4l2 sensor drivers on both DT- and ACPI-based
platforms to retrieve a reference to the clock producer from firmware.

This helper behaves the same as clk_get_optional() except where there is
no clock producer like typically in ACPI-based platforms.
For ACPI-based platforms the function will read the "clock-frequency"
property (_DSD ACPI property) and register a fixed frequency clock with
the frequency indicated in the property.

Signed-off-by: Mehdi Djait <mehdi.djait@linux.intel.com>
---
 drivers/media/v4l2-core/v4l2-common.c | 38 +++++++++++++++++++++++++++
 include/media/v4l2-common.h           | 19 ++++++++++++++
 2 files changed, 57 insertions(+)

Hi Mehdi,

On Thu, Feb 27, 2025 at 10:26:43AM +0100, Mehdi Djait wrote:
> Introduce a helper for v4l2 sensor drivers on both DT- and ACPI-based
> platforms to retrieve a reference to the clock producer from firmware.
> 
> This helper behaves the same as clk_get_optional() except where there is
> no clock producer like typically in ACPI-based platforms.
> For ACPI-based platforms the function will read the "clock-frequency"
> property (_DSD ACPI property) and register a fixed frequency clock with
> the frequency indicated in the property.
> 
> Signed-off-by: Mehdi Djait <mehdi.djait@linux.intel.com>
> ---
>  drivers/media/v4l2-core/v4l2-common.c | 38 +++++++++++++++++++++++++++
>  include/media/v4l2-common.h           | 19 ++++++++++++++
>  2 files changed, 57 insertions(+)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-common.c b/drivers/media/v4l2-core/v4l2-common.c
> index 0a2f4f0d0a07..308a13536ac3 100644
> --- a/drivers/media/v4l2-core/v4l2-common.c
> +++ b/drivers/media/v4l2-core/v4l2-common.c
> @@ -34,6 +34,9 @@
>   * Added Gerd Knorrs v4l1 enhancements (Justin Schoeman)
>   */
>  
> +#include <linux/clk.h>
> +#include <linux/clkdev.h>
> +#include <linux/clk-provider.h>
>  #include <linux/module.h>
>  #include <linux/types.h>
>  #include <linux/kernel.h>
> @@ -636,3 +639,38 @@ int v4l2_link_freq_to_bitmap(struct device *dev, const u64 *fw_link_freqs,
>  	return 0;
>  }
>  EXPORT_SYMBOL_GPL(v4l2_link_freq_to_bitmap);
> +
> +struct clk *devm_v4l2_sensor_clk_get(struct device *dev, const char *id)
> +{
> +	struct clk_hw *clk_hw;
> +	struct clk *clk;
> +	char *clk_name;
> +	u32 rate;
> +	int ret;
> +
> +	clk = devm_clk_get_optional(dev, id);
> +	if (clk || IS_ERR(clk))
> +		return clk;
> +
> +	if (!is_acpi_node(dev_fwnode(dev)))
> +		return ERR_PTR(-EINVAL);
> +
> +	ret = device_property_read_u32(dev, "clock-frequency", &rate);
> +	if (ret)
> +		return ERR_PTR(ret);
> +
> +	if (!id) {
> +		clk_name = devm_kasprintf(dev, GFP_KERNEL, "clk-%s",
> +					  dev_name(dev));

You could just assign to "id" and omit clk_name altogether.

> +		if (!clk_name)
> +			return ERR_PTR(-ENOMEM);
> +	}
> +
> +	clk_hw = devm_clk_hw_register_fixed_rate(dev, id ? id : clk_name, NULL,
> +						 0, rate);
> +	if (IS_ERR(clk_hw))
> +		return ERR_CAST(clk_hw);
> +
> +	return clk_hw->clk;
> +}
> +EXPORT_SYMBOL_GPL(devm_v4l2_sensor_clk_get);
> diff --git a/include/media/v4l2-common.h b/include/media/v4l2-common.h
> index 63ad36f04f72..6446575b2a75 100644
> --- a/include/media/v4l2-common.h
> +++ b/include/media/v4l2-common.h
> @@ -573,6 +573,25 @@ int v4l2_link_freq_to_bitmap(struct device *dev, const u64 *fw_link_freqs,
>  			     unsigned int num_of_driver_link_freqs,
>  			     unsigned long *bitmap);
>  
> +/**
> + * devm_v4l2_sensor_clk_get - lookup and obtain a reference to an optional clock
> + *			      producer for a camera sensor.
> + *
> + * @dev: device for v4l2 sensor clock "consumer"
> + * @id: clock consumer ID
> + *
> + * This function behaves the same way as clk_get_optional() except where there
> + * is no clock producer like in ACPI-based platforms.
> + * For ACPI-based platforms, the function will read the "clock-frequency"
> + * property (_DSD ACPI property) and register a fixed-clock with the frequency

s/property (_DSD ACPI property)/ACPI _DSD property/

> + * indicated in the property.
> + *
> + * Return:
> + * * %pointer to a struct clk: Success
> + * * %valid IS_ERR() condition containing errno: Failure

% should precede a value, but neither is describing a value here. How
about:

Return:
A pointer to a struct clk on success or an error code on failure.

> + */
> +struct clk *devm_v4l2_sensor_clk_get(struct device *dev, const char *id);
> +
>  static inline u64 v4l2_buffer_get_timestamp(const struct v4l2_buffer *buf)
>  {
>  	/*

On Fri, Mar 07, 2025 at 11:51:58AM +0000, Sakari Ailus wrote:
> > +	int ret;
> > +
> > +	clk = devm_clk_get_optional(dev, id);
> > +	if (clk || IS_ERR(clk))

I forgot this bit earlier. The IS_ERR() check is redundant.

> > +		return clk;
> > +
> > +	if (!is_acpi_node(dev_fwnode(dev)))
> > +		return ERR_PTR(-EINVAL);

How about -ENOENT? That's what devm_clk_get() returns when there's no such
clock.