Hello Nylon, On Wed, Feb 01, 2023 at 04:56:42PM +0800, Nylon Chen wrote: > Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx> 於 2023年1月30日 週一 下午6:17寫道： > > On Mon, Jan 30, 2023 at 05:32:29PM +0800, Nylon Chen wrote: > > > The `frac` variable represents the pulse inactive time, and the result of > > > this algorithm is the pulse active time. Therefore, we must reverse the > > > result. > > > > > > The reference is SiFive FU740-C000 Manual[0]. > > > > > > [0]: https://sifive.cdn.prismic.io/sifive/1a82e600-1f93-4f41-b2d8-86ed8b16acba_fu740-c000-manual-v1p6.pdf > > > > > > Signed-off-by: Nylon Chen <nylon.chen@xxxxxxxxxx> > > > --- > > > drivers/pwm/pwm-sifive.c | 1 + > > > 1 file changed, 1 insertion(+) > > > > > > diff --git a/drivers/pwm/pwm-sifive.c b/drivers/pwm/pwm-sifive.c > > > index 62b6acc6373d..a5eda165d071 100644 > > > --- a/drivers/pwm/pwm-sifive.c > > > +++ b/drivers/pwm/pwm-sifive.c > > > @@ -158,6 +158,7 @@ static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm, > > > frac = DIV64_U64_ROUND_CLOSEST(num, state->period); > > > /* The hardware cannot generate a 100% duty cycle */ > > > frac = min(frac, (1U << PWM_SIFIVE_CMPWIDTH) - 1); > > > + frac = (1U << PWM_SIFIVE_CMPWIDTH) - 1 - frac; > > > > The same problem exists in pwm_sifive_get_state(), doesn't it? > > > > As fixing this is an interruptive change anyhow, this is the opportunity > > to align the driver to the rules tested by PWM_DEBUG. > > > > The problems I see in the driver (only checked quickly, so I might be > > wrong): > > > > - state->period != ddata->approx_period isn't necessarily a problem. If > > state->period > ddata->real_period that's fine and the driver should > > continue > > > > - frac = DIV64_U64_ROUND_CLOSEST(num, state->period); > > is wrong for two reasons: > > it should round down and use the real period. > > > I need a little time to clarify your assumptions. If possible, I will > make similar changes. > > e.g. > rounddown(num, state->period); > if (state->period < ddata->approx_period) > ... the idea is that for a given request apply should do the following to select the hardware setting: - Check polarity, if the hardware doesn't support it, return -EINVAL. (A period always starts with the active phase for the duration of duty_cycle. For normal polarity active = high.) - Pick the biggest period length possible that is not bigger than the requested period. - For the picked period, select the biggest duty_cycle possible that is not bigger than the requested duty_cycle. Then if possible switch to the selected setting in an atomic step. Does this clearify your doubts? Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | https://www.pengutronix.de/ |
Attachment:
signature.asc
Description: PGP signature
