Hello Geert,
On Tue, Mar 12, 2024 at 09:11:42AM +0100, Geert Uytterhoeven wrote:
> On Tue, Mar 12, 2024 at 8:20 AM Uwe Kleine-König
> <u.kleine-koenig@xxxxxxxxxxxxxx> wrote:
> > On Tue, Feb 20, 2024 at 07:43:17PM +0000, Biju Das wrote:
> > > --- /dev/null
> > > +++ b/drivers/pwm/pwm-rzg2l-gpt.c
> > > +static u64 calculate_period_or_duty(struct rzg2l_gpt_chip *rzg2l_gpt, u32 val, u8 prescale)
> > > +{
> > > + u64 tmp, d;
> > > +
> > > + /*
> > > + * Rate is in MHz and is always integer for peripheral clk
> > > + * 2^32 * 2^10 (prescalar) * 10^9 > 2^64
> > > + * 2^32 * 2^10 (prescalar) * 10^6 < 2^64
> > > + * Multiply val with prescalar first, if the result is less than
> > > + * 2^34, then multiply by 10^9. Otherwise divide nr and dr by 10^3
> > > + * so that it will never overflow.
> > > + */
> > > +
> > > + tmp = (u64)val << (2 * prescale);
> > > + if (tmp <= (1ULL << 34)) {
> >
> > I would have written that as:
> >
> > if (tmp >> 34 == 0)
> >
> > (which implements tmp < (1ULL << 34), which doesn't matter much).
> >
> > > + tmp *= NSEC_PER_SEC;
> > > + d = rzg2l_gpt->rate;
> > > + } else {
> > > + tmp *= div64_u64(NSEC_PER_SEC, KILO);
> >
> > I don't know if the compiler is clever enough to not calculate that
> > every time?
>
> Not on 32-bit when written that way.
>
> > Also using div64_u64 is too heavy given that both values fit
> > into an u32.
>
> Indeed, so "NSEC_PER_SEC / KILO" should be fine.
ack.
> I guess NSEC_PER_MSEC would be too obfuscating?
or USEC_PER_SEC? Not sure. Also I'm unsure if using KILO instead of 1000
is really an improvement.
If you know that the clkrate is a multiple of 1000 there is no reason to
not use clkrate / 1000 unconditionally. So maybe use
rzg2l_gpt->rate_kHz (and error out in .probe if the rate isn't a
multiple of 1000?)
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |
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