On Wed, Apr 20, 2022 at 08:08:34PM +0200, Geert Uytterhoeven wrote:
> Hi Uwe,
>
> On Wed, Apr 20, 2022 at 2:12 PM Uwe Kleine-König
> <u.kleine-koenig@xxxxxxxxxxxxxx> wrote:
> > The newly computed register values are intended to exactly match the
> > previously computed values. The main improvement is that the prescaler
> > is computed without a loop that involves two divisions in each step.
> > This uses the fact, that prescalers[i] = 1 << (2 * i).
> >
> > Assuming a moderately smart compiler, the needed number of divisions for
> > the case where the requested period is too big, is reduced from 5 to 2.
> >
> > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
>
> Thanks for your patch!
>
> > --- a/drivers/pwm/pwm-renesas-tpu.c
> > +++ b/drivers/pwm/pwm-renesas-tpu.c
> > @@ -244,7 +244,6 @@ static void tpu_pwm_free(struct pwm_chip *chip, struct pwm_device *pwm)
> > static int tpu_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
> > int duty_ns, int period_ns, bool enabled)
> > {
> > - static const unsigned int prescalers[] = { 1, 4, 16, 64 };
> > struct tpu_pwm_device *tpd = pwm_get_chip_data(pwm);
> > struct tpu_device *tpu = to_tpu_device(chip);
> > unsigned int prescaler;
> > @@ -254,26 +253,47 @@ static int tpu_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
> > u32 duty;
> > int ret;
> >
> > + clk_rate = clk_get_rate(tpu->clk);
> > +
> > + period = clk_rate / (NSEC_PER_SEC / period_ns);
> > +
> > /*
> > - * Pick a prescaler to avoid overflowing the counter.
> > - * TODO: Pick the highest acceptable prescaler.
> > + * Find the minimal prescaler in [0..3] such that
> > + *
> > + * period >> (2 * prescaler) < 0x10000
>
> scripts/checkpatch.pl:
> WARNING: please, no space before tabs
>
> > + *
> > + * This could be calculated using something like:
> > + *
> > + * prescaler = max(ilog2(period) / 2, 7) - 7;
>
> WARNING: please, no space before tabs
>
> The rest LGTM, so
> Reviewed-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
@Thierry: Assuming you agree to this patch, too: Should I resend for the
checkpack warning (I'd s/\t/ /), or do you want to fixup at apply
time?
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |
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