linux-kernel - RE: [PATCH v15 05/10] clk: Add Sunplus SP7021 clock driver

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Date:   Thu, 19 May 2022 02:16:50 +0000
From:   qinjian[覃健] <qinjian@...lus1.com>
To:     Stephen Boyd <sboyd@...nel.org>
CC:     "krzysztof.kozlowski@...aro.org" <krzysztof.kozlowski@...aro.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mturquette@...libre.com" <mturquette@...libre.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "maz@...nel.org" <maz@...nel.org>,
        "p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "arnd@...db.de" <arnd@...db.de>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>
Subject: RE: [PATCH v15 05/10] clk: Add Sunplus SP7021 clock driver

> > > > +
> > > > +                               df_quotient  = df / m;
> > > > +                               df_remainder = ((df % m) * 1000) / m;
> > > > +
> > > > +                               if (freq > df_quotient) {
> > > > +                                       df_quotient  = freq - df_quotient - 1;
> > > > +                                       df_remainder = 1000 - df_remainder;
> > >
> > > Where does 1000 come from?
> >
> > 1000 is come from "borrow 1" in last operation.
> 
> It's scaling the value right? What is being scaled? Are we converting
> units to Hz from kHz?

Here just using integer replacement floating point operation, for example:
df = 13, m = 3
13 / 3 = 4.33333333
df_quotient = 4
df_remainder = 0.3333333 * 1000 (accurate to 3 decimal places) = 333