| Message ID | 20230130093229.27489-3-nylon.chen@sifive.com |
|---|---|
| State | Changes Requested |
| Headers | show |
| Series | Change PWM-controlled LED pin active mode and algorithm | expand |
Hi Nylon, On Mon, Jan 30, 2023 at 10:32 AM Nylon Chen <nylon.chen@sifive.com> 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@sifive.com> Thanks for your patch! > --- 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; Shouldn't the inversion be done before the hardware limitation fixup? > > mutex_lock(&ddata->lock); > if (state->period != ddata->approx_period) { Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org 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
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@sifive.com> > --- > 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. Best regards Uwe
Hi Geert, Thanks for your reply. Geert Uytterhoeven <geert@linux-m68k.org> 於 2023年1月30日 週一 下午5:53寫道： > > Hi Nylon, > > On Mon, Jan 30, 2023 at 10:32 AM Nylon Chen <nylon.chen@sifive.com> 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@sifive.com> > > Thanks for your patch! > > > --- 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; > > Shouldn't the inversion be done before the hardware limitation fixup? I think your inference is correct, I will use it. thanks a lot. > > > > > mutex_lock(&ddata->lock); > > if (state->period != ddata->approx_period) { > > Gr{oetje,eeting}s, > > Geert > > -- > Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org > > 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
Hi Uwe, Thanks for your reply. Uwe Kleine-König <u.kleine-koenig@pengutronix.de> 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@sifive.com> > > --- > > 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) ... thanks a lot. > Best regards > Uwe > > -- > Pengutronix e.K. | Uwe Kleine-König | > Industrial Linux Solutions | https://www.pengutronix.de/ |
Hi Uwe, Uwe Kleine-König <u.kleine-koenig@pengutronix.de> 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@sifive.com> > > --- > > 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. are you mean state->period is a redundancy variable so we can use ddata->real_period directly? it seems reasonable, but I don't get your point, why do we need to change the algorithm to DIV_ROUND_DOWN_ULL() and change the if-else condition. frac = DIV_ROUND_DOWN_ULL(num, ddata->real_period); if (state->period < ddata->approx_period) { ... } > > Best regards > Uwe > > -- > Pengutronix e.K. | Uwe Kleine-König | > Industrial Linux Solutions | https://www.pengutronix.de/ |
Hi Uwe, Nylon Chen <nylon.chen@sifive.com> 於 2023年2月3日 週五 下午4:06寫道： > > Hi Uwe, > > Uwe Kleine-König <u.kleine-koenig@pengutronix.de> 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@sifive.com> > > > --- > > > 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 have some results from my observations regarding the questions you raised. I don't know if what we are thinking is the same thing. If my assumptions are different from yours, please let me know. Thanks. > are you mean state->period is a redundancy variable so we can use > ddata->real_period directly? > > it seems reasonable, but I don't get your point, why do we need to > change the algorithm to DIV_ROUND_DOWN_ULL() and change the if-else > condition. > > frac = DIV_ROUND_DOWN_ULL(num, ddata->real_period); > if (state->period < ddata->approx_period) { > ... > } > > > > > Best regards > > Uwe > > > > -- > > Pengutronix e.K. | Uwe Kleine-König | > > Industrial Linux Solutions | https://www.pengutronix.de/ |
Hello Nylon, On Wed, Feb 01, 2023 at 04:56:42PM +0800, Nylon Chen wrote: > Uwe Kleine-König <u.kleine-koenig@pengutronix.de> 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@sifive.com> > > > --- > > > 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
Hi Uwe Thanks for your reply. Uwe Kleine-König <u.kleine-koenig@pengutronix.de> 於 2023年3月1日 週三 下午5:21寫道： > > Hello Nylon, > > On Wed, Feb 01, 2023 at 04:56:42PM +0800, Nylon Chen wrote: > > Uwe Kleine-König <u.kleine-koenig@pengutronix.de> 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@sifive.com> > > > > --- > > > > 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? I need a little time to clarify your assumptions. Thanks again. > > Best regards > Uwe > > -- > Pengutronix e.K. | Uwe Kleine-König | > Industrial Linux Solutions | https://www.pengutronix.de/ |
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; mutex_lock(&ddata->lock); if (state->period != ddata->approx_period) {
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@sifive.com> --- drivers/pwm/pwm-sifive.c | 1 + 1 file changed, 1 insertion(+)