Hi Uwe I'm glad the example was helpful to you. I will double-check and verify my implementation once again. Thank you for your assistance. Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx> 於 2023年9月8日 週五 下午10:50寫道： > > Hello, > > On Fri, Sep 08, 2023 at 06:41:00PM +0800, Nylon Chen wrote: > > Sorry it's so long ago. > > > > I have completed the implementation of the new version, but there is > > one thing about this letter that I still don't quite understand. > > > > 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 > > > > I still don’t quite understand the description of this paragraph. > > > > state->period != ddate->approx_period seems to be used to compare the > > results of the previous and next two times. > > There are two things to consider: > > - usually the hardware doesn't support all requestable states because > the hardware's quantum is > 1 ns. That is, it might for example > support periods in the form (160 ns * i / 3) for i in 1 .. 1023. > > If this hardware runs with i = 500 (that is period ~= 26666.66 > ns) because the first channel is configured to run with period = > 26667, and .request is called for the 2nd channel with .period = > 26700 ns, there is no need to refuse that, because 26666.66 is the > best possible approximation for 26700 ns anyhow. > > - .apply is supposed to implement the highest possible period that > isn't bigger than the requested period. So in the above case even if > the hardware runs at 26666.66 ns without the possibility to change > that, a request to configure for period = 30000 ns could succeed (and > keep 26666.66 ns). > > > Would you suggest I send the new implementation version before > > continuing the discussion? > > Note that the above implements the optimal behaviour for a driver. > (For some definition of "optimal" that admittedly also yields strange > behaviour at times. The reasoning for this to the be thing to implement > is, that's the corner cases are easier to implement, idempotency is > possible and it's easier to work with than rounding to the nearest > possible value.) > > While I'd like to see the sifive driver to implement this optimal > behaviour, it's not mandatory that you convert the driver to that > behaviour. Just make sure to not make it worse. > > So to answer your question: If you understood what I wrote above and are > motivated to improve the driver, it would be great to do that before the > next review round. > > Best regards > Uwe > > -- > Pengutronix e.K. | Uwe Kleine-König | > Industrial Linux Solutions | https://www.pengutronix.de/ |
