On Fri, 21 Apr 2023 at 08:16, Nylon Chen <nylon.chen@xxxxxxxxxx> wrote: > > Hi Emil, > > Emil Renner Berthing <emil.renner.berthing@xxxxxxxxxxxxx> 於 2023年4月20日 > 週四 下午6:46寫道： > > > > On Thu, 20 Apr 2023 at 12:41, Nylon Chen <nylon.chen@xxxxxxxxxx> wrote: > > > > > > Hi, Emil > > > > > > Emil Renner Berthing <emil.renner.berthing@xxxxxxxxxxxxx> 於 2023年4月20日 週四 下午6:04寫道： > > > > > > > > On Thu, 20 Apr 2023 at 11:35, Nylon Chen <nylon.chen@xxxxxxxxxx> 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] > > > > > > > > > > Link: https://sifive.cdn.prismic.io/sifive/1a82e600-1f93-4f41-b2d8-86ed8b16acba_fu740-c000-manual-v1p6.pdf [0] > > > > > > > > > > Acked-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx> > > > > > Reviewed-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx> > > > > > Signed-off-by: Nylon Chen <nylon.chen@xxxxxxxxxx> > > > > > Signed-off-by: Vincent Chen <vincent.chen@xxxxxxxxxx> > > > > > --- > > > > > drivers/pwm/pwm-sifive.c | 9 ++++++--- > > > > > 1 file changed, 6 insertions(+), 3 deletions(-) > > > > > > > > > > diff --git a/drivers/pwm/pwm-sifive.c b/drivers/pwm/pwm-sifive.c > > > > > index 393a4b97fc19..d5d5f36da297 100644 > > > > > --- a/drivers/pwm/pwm-sifive.c > > > > > +++ b/drivers/pwm/pwm-sifive.c > > > > > @@ -132,13 +132,13 @@ static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm, > > > > > { > > > > > struct pwm_sifive_ddata *ddata = pwm_sifive_chip_to_ddata(chip); > > > > > struct pwm_state cur_state; > > > > > - unsigned int duty_cycle; > > > > > + unsigned int duty_cycle, period; > > > > > unsigned long long num; > > > > > bool enabled; > > > > > int ret = 0; > > > > > u32 frac; > > > > > > > > > > - if (state->polarity != PWM_POLARITY_INVERSED) > > > > > + if (state->polarity != PWM_POLARITY_NORMAL && state->polarity != PWM_POLARITY_INVERSED) > > > > > return -EINVAL; > > > > > > > > > > cur_state = pwm->state; > > > > > @@ -154,10 +154,13 @@ static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm, > > > > > * calculating the register values first and then writing them > > > > > * consecutively > > > > > */ > > > > > + period = max(state->period, ddata->approx_period); > > > > > > > > Hi Nylon, > > > > > > > > I don't understand this patch. You introduce this new variable, > > > > period, and set it here but you never seem to use it. If you planned > > > > to use it instead of state->period below, why should it be the max of > > > > the old period and what is requested? What happens if the consumer > > > > wants to lower the period? > > > Sorry this was an oversight on my part, there was a line correction that didn't change to > > > - frac = DIV64_U64_ROUND_CLOSEST(num, state->period); > > > + frac = DIV64_U64_ROUND_CLOSEST(num, period); > > > > I see, so then my second question was why period needs to be the > > larger of the previous period and the requested period. > > > > What happens if the requested period, state->period, is lower than the > > old period, ddata->approx_period? Then the period will be changed to > > state->period below, but the calculations will be made using period = > > ddata->approx_period, right? > > Your understanding is correct. According to the new algorithm proposed > by Uwe, the goal is to: > Pick the biggest period length possible that is not bigger than the > requested period. Right, and to be clear: this patch doesn't do that. If the previous period in ddata->approx_period is bigger than the requested period in state->period, it will do the frac calculations with the old period, but still set the period to the shorter requested period. > > > > > > > > Also above you now allow both PWM_POLARITY_NORMAL and > > > > PWM_POLARITY_INVERSED but you treat both cases the same. > > > I may have misunderstood what Uwe means here, I will confirm again here > > > > > > > > /Emil > > > > > > > > > num = (u64)duty_cycle * (1U << PWM_SIFIVE_CMPWIDTH); > > > > > frac = DIV64_U64_ROUND_CLOSEST(num, state->period); > > > > > - /* The hardware cannot generate a 100% duty cycle */ > > > > > frac = min(frac, (1U << PWM_SIFIVE_CMPWIDTH) - 1); > > > > > + /* The hardware cannot generate a 100% duty cycle */ > > > > > + frac = (1U << PWM_SIFIVE_CMPWIDTH) - 1 - frac; > > > > > + > > > > > > > > > > mutex_lock(&ddata->lock); > > > > > if (state->period != ddata->approx_period) { > > > > > -- > > > > > 2.40.0 > > > > >
