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>
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
