Re: [PATCH v2 1/4] clk: Introduce clk_hw_set_spread_spectrum

Marco Felsch
2025-02-06T09:47:45Z

On 25-02-06, Peng Fan wrote:
> > Subject: Re: [PATCH v2 1/4] clk: Introduce
> > clk_hw_set_spread_spectrum
> >
> > Hi Peng,
> >
> > On 25-02-05, Peng Fan (OSS) wrote:
> > > From: Peng Fan <peng.fan@nxp.com>
> > >
> > > 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 | 34 ++++++++++++++++++++++++++++++++++
> > > include/linux/clk-provider.h | 32
> > ++++++++++++++++++++++++++++++++
> > > include/linux/clk.h | 22 ++++++++++++++++++++++
> > > 3 files changed, 88 insertions(+)
> > >
> > > diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c index
> > >
> > cf7720b9172ff223d86227aad144e15375ddfd86..e11f9615e683af52c7
> > 19d4c8419b
> > > d30f369f301b 100644
> > > --- a/drivers/clk/clk.c
> > > +++ b/drivers/clk/clk.c
> > > @@ -2790,6 +2790,40 @@ 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, unsigned int
> > modfreq,
> > > + unsigned int spreaddepth, enum
> > clk_ssc_method method,
> > > + bool enable)
> > > +{
> > > + struct clk_spread_spectrum clk_ss;
> > > + struct clk_core *core;
> > > + int ret;
> > > +
> > > + if (!hw)
> > > + return 0;
> > > +
> > > + core = hw->core;
> > > +
> > > + clk_ss.modfreq = modfreq;
> > > + clk_ss.spreaddepth = spreaddepth;
> > > + clk_ss.method = method;
> > > + clk_ss.enable = enable;
> > > +
> > > + 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, &clk_ss);
> > > +
> > > + 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
> > >
> > 2e6e603b749342931c0d0693c3e72b62c000791b..ac0270cc9ec13395
> > 4b1f8dcffed0
> > > 15723bd1ff5d 100644
> > > --- a/include/linux/clk-provider.h
> > > +++ b/include/linux/clk-provider.h
> > > @@ -84,6 +84,28 @@ struct clk_duty {
> > > unsigned int den;
> > > };
> > >
> > > +/* Aligned with dtschema/schemas/clock/clock.yaml */ enum
> > > +clk_ssc_method {
> > > + CLK_SSC_CENTER_SPREAD,
> > > + CLK_SSC_UP_SPREAD,
> > > + CLK_SSC_DOWN_SPREAD,
> > > +};
> > > +
> > > +/**
> > > + * struct clk_spread_spectrum - Structure encoding spread spectrum
> > of
> > > +a clock
> > > + *
> > > + * @modfreq: Modulation frequency
> > > + * @spreadpercent: Modulation percent
> > > + * @method: Modulation method
> > > + * @enable: Modulation enable or disable
> > > + */
> > > +struct clk_spread_spectrum {
> > > + unsigned int modfreq;
> > > + unsigned int spreaddepth;
> >
> > Please use per mil as unit since I noticed that 0.x% is a common value
> > too.
>
> I use " The modulation depth in permyriad " in dt-schema, since
> Dario said ST chips has permyriad.

Ah okay, thanks for the explanation, this wasn't clear since also the
comment says: "Modulation percent". I wouldn't call it permyriad or
per_myriad since this unit is rather rare. Instead I would call it "basis
point" so the variable name could be 'spread_bp'. While on it, we could
rename modfreq to modfreq_hz to make it clear.

Regards,
Marco

>
> So change it to moddepth_per_myriad?
>
> Thanks,
> Peng.
>
> >
> > Regards,
> > Marco
> >
> >
> > > + enum clk_ssc_method method;
> > > + bool enable;
> > > +};
> > > +
> > > /**
> > > * 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 +200,11 @@ 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 +282,8 @@ 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);
> > > @@ -1404,6 +1433,9 @@ 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, unsigned int
> > modfreq,
> > > + unsigned int spreaddepth, enum
> > clk_ssc_method method,
> > > + bool enable);
> > >
> > > static inline void __clk_hw_set_clk(struct clk_hw *dst, struct clk_hw
> > > *src) { diff --git a/include/linux/clk.h b/include/linux/clk.h index
> > >
> > b607482ca77e987b9344c38f25ebb5c8d35c1d39..49a7f7eb8b03233e
> > 11cd3b927688
> > > 96c4e45c4e7c 100644
> > > --- a/include/linux/clk.h
> > > +++ b/include/linux/clk.h
> > > @@ -858,6 +858,21 @@ int clk_set_rate(struct clk *clk, unsigned
> > long rate);
> > > */
> > > int clk_set_rate_exclusive(struct clk *clk, unsigned long rate);
> > >
> > > +/**
> > > + * clk_set_spread_spectrum - set the spread spectrum for a clock
> > > + * @clk: clock source
> > > + * @modfreq: modulation freq
> > > + * @spreadpercent: modulation percentage
> > > + * @method: down spread, up spread, center spread or else
> > > + * @enable: enable or disable
> > > + *
> > > + * Configure the spread spectrum parameters for a clock.
> > > + *
> > > + * Returns success (0) or negative errno.
> > > + */
> > > +int clk_set_spread_spectrum(struct clk *clk, unsigned int modfreq,
> > > + unsigned int spreadpercent, unsigned int
> > method,
> > > + bool enable);
> > > /**
> > > * clk_has_parent - check if a clock is a possible parent for another
> > > * @clk: clock source
> > > @@ -1088,6 +1103,13 @@ static inline int
> > clk_set_rate_exclusive(struct clk *clk, unsigned long rate)
> > > return 0;
> > > }
> > >
> > > +static inline int clk_set_spread_spectrum(struct clk *clk, unsigned
> > int modfreq,
> > > + unsigned int spreadpercent,
> > > + unsigned int method, bool
> > enable) {
> > > + return 0;
> > > +}
> > > +
> > > static inline long clk_round_rate(struct clk *clk, unsigned long
> > > rate) {
> > > return 0;
> > >
> > > --
> > > 2.37.1
> > >
> > >
> > >
>