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.
+ *
  * @recalc_accuracy: Recalculate the accuracy of this clock. The clock accuracy
  *		is expressed in ppb (parts per billion). The parent accuracy is
  *		an input parameter.
@@ -255,6 +278,8 @@ struct clk_ops {
 	int		(*set_rate_and_parent)(struct clk_hw *hw,
 				    unsigned long rate,
 				    unsigned long parent_rate, u8 index);
+	int		(*set_spread_spectrum)(struct clk_hw *hw,
+					       struct clk_spread_spectrum *clk_ss);
 	unsigned long	(*recalc_accuracy)(struct clk_hw *hw,
 					   unsigned long parent_accuracy);
 	int		(*get_phase)(struct clk_hw *hw);
@@ -1430,6 +1455,7 @@ void clk_hw_get_rate_range(struct clk_hw *hw, unsigned long *min_rate,
 			   unsigned long *max_rate);
 void clk_hw_set_rate_range(struct clk_hw *hw, unsigned long min_rate,
 			   unsigned long max_rate);
+int clk_hw_set_spread_spectrum(struct clk_hw *hw, struct clk_spread_spectrum *conf);
 
 static inline void __clk_hw_set_clk(struct clk_hw *dst, struct clk_hw *src)
 {

-- 
2.37.1

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

On Tue, Sep 02, 2025 at 06:01:12PM -0400, Brian Masney wrote:
>>   *
>> + * @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.

This is better. I will update in v3.

Thanks,
Peng

>
>Everything else looks good to me.
>
>Brian
>