Re: [PATCH v2 1/3] clk: Introduce clk_hw_set_spread_spectrum

[Brian Masney <bmasney@redhat.com>]

On Mon, Sep 01, 2025 at 11:51:45AM +0800, Peng Fan wrote:
> Add clk_hw_set_spread_spectrum to configure a clock to enable spread
> spectrum feature. set_spread_spectrum ops is added for clk drivers to
> have their own hardware specific implementation.
> 
> Signed-off-by: Peng Fan <peng.fan@nxp.com>
> ---
>  drivers/clk/clk.c            | 26 ++++++++++++++++++++++++++
>  include/linux/clk-provider.h | 26 ++++++++++++++++++++++++++
>  2 files changed, 52 insertions(+)
> 
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index b821b2cdb155331c85fafbd2fac8ab3703a08e4d..06db8918a1b35e3280e565272bc4603a88295a92 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -2802,6 +2802,32 @@ int clk_set_max_rate(struct clk *clk, unsigned long rate)
>  }
>  EXPORT_SYMBOL_GPL(clk_set_max_rate);
>  
> +int clk_hw_set_spread_spectrum(struct clk_hw *hw, struct clk_spread_spectrum *conf)
> +{
> +	struct clk_core *core;
> +	int ret;
> +
> +	if (!hw)
> +		return 0;
> +
> +	core = hw->core;
> +
> +	clk_prepare_lock();
> +
> +	ret = clk_pm_runtime_get(core);
> +	if (ret)
> +		goto fail;
> +
> +	if (core->ops->set_spread_spectrum)
> +		ret = core->ops->set_spread_spectrum(hw, conf);
> +
> +	clk_pm_runtime_put(core);
> +
> +fail:
> +	clk_prepare_unlock();
> +	return ret;
> +}
> +
>  /**
>   * clk_get_parent - return the parent of a clk
>   * @clk: the clk whose parent gets returned
> diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
> index 630705a47129453c241f1b1755f2c2f2a7ed8f77..251035a96244c34ff2cbaaa349a08f4ea094e7fc 100644
> --- a/include/linux/clk-provider.h
> +++ b/include/linux/clk-provider.h
> @@ -84,6 +84,24 @@ struct clk_duty {
>  	unsigned int den;
>  };
>  
> +#define	CLK_SSC_NO_SPREAD	0
> +#define	CLK_SSC_CENTER_SPREAD	1
> +#define	CLK_SSC_UP_SPREAD	2
> +#define	CLK_SSC_DOWN_SPREAD	3
> +
> +/**
> + * struct clk_spread_spectrum - Structure encoding spread spectrum of a clock
> + *
> + * @modfreq_hz:		Modulation frequency
> + * @spread_bp:		Modulation percent in permyriad
> + * @method:		Modulation method
> + */
> +struct clk_spread_spectrum {
> +	u32 modfreq_hz;
> +	u32 spread_bp;
> +	u32 method;
> +};
> +
>  /**
>   * struct clk_ops -  Callback operations for hardware clocks; these are to
>   * be provided by the clock implementation, and will be called by drivers
> @@ -178,6 +196,11 @@ struct clk_duty {
>   *		separately via calls to .set_parent and .set_rate.
>   *		Returns 0 on success, -EERROR otherwise.
>   *
> + * @set_spread_spectrum: Configure the modulation frequency, modulation percentage
> + *		and method. This callback is optional for clocks that does not
> + *		support spread spectrum feature or no need to enable this feature.
> + *		Returns 0 on success, -EERROR otherwise.

I think it would be worthwhile to call out in the kdocs that this helps
to reduce EMI. How does this sound?

@set_spread_spectrum: Optional callback used to configure the spread
		spectrum modulation frequency, percentage, and method
		to reduce EMI by spreading the clock frequency over a
		wider range.
		Returns 0 on success, -EERROR otherwise.

Everything else looks good to me.

Brian