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Message-ID: <aLdpKEwfqP448eMd@x1>
Date: Tue, 2 Sep 2025 18:01:12 -0400
From: Brian Masney <bmasney@...hat.com>
To: Peng Fan <peng.fan@....com>
Cc: Michael Turquette <mturquette@...libre.com>,
Stephen Boyd <sboyd@...nel.org>,
Sudeep Holla <sudeep.holla@....com>,
Cristian Marussi <cristian.marussi@....com>,
Marco Felsch <m.felsch@...gutronix.de>,
Dan Carpenter <dan.carpenter@...aro.org>,
Geert Uytterhoeven <geert@...ux-m68k.org>,
linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
arm-scmi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 1/3] clk: Introduce clk_hw_set_spread_spectrum
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@....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
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