| Message ID | 20240126074045.20159-3-nylon.chen@sifive.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | Change PWM-controlled LED pin active mode and algorithm | expand |
Hello, Regarding the Subject: The patch has nothing to do with an LED, has it? On Fri, Jan 26, 2024 at 03:40:44PM +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. Please break lines at 75 columns in the commit log. > 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] I looked at Figure 29 in this document (version v1p6, pdf page 148). Not sure I understand that correctly, but I expect that the output of the ">=?" node below pwmcmp0 to become 1 if pwms has reached pwmcmp0, is that right? In that case this output is zero when pwmcount is zero and then pwmcmp0ip is zero, too. So a period starts with the inactive part and so it's inversed polarity. What made you think that the current driver implementation is wrong? > Co-developed-by: Zong Li <zong.li@sifive.com> > Signed-off-by: Zong Li <zong.li@sifive.com> > Co-developed-by: Vincent Chen <vincent.chen@sifive.com> > Signed-off-by: Vincent Chen <vincent.chen@sifive.com> > Signed-off-by: Nylon Chen <nylon.chen@sifive.com> > --- > drivers/pwm/pwm-sifive.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/drivers/pwm/pwm-sifive.c b/drivers/pwm/pwm-sifive.c > index eabddb7c7820..b07c8598bb21 100644 > --- a/drivers/pwm/pwm-sifive.c > +++ b/drivers/pwm/pwm-sifive.c > @@ -113,6 +113,7 @@ static int pwm_sifive_get_state(struct pwm_chip *chip, struct pwm_device *pwm, > u32 duty, val; > > duty = readl(ddata->regs + PWM_SIFIVE_PWMCMP(pwm->hwpwm)); > + duty = (1U << PWM_SIFIVE_CMPWIDTH) - 1 - duty; I find it irritating that both values are assigned to duty. I'd spend another variable and make this: inactive = readl(ddata->regs + PWM_SIFIVE_PWMCMP(pwm->hwpwm)); duty = (1U << PWM_SIFIVE_CMPWIDTH) - 1 - inactive; > > state->enabled = duty > 0; > > @@ -123,11 +124,10 @@ static int pwm_sifive_get_state(struct pwm_chip *chip, struct pwm_device *pwm, > state->period = ddata->real_period; > state->duty_cycle = > (u64)duty * ddata->real_period >> PWM_SIFIVE_CMPWIDTH; > - state->polarity = PWM_POLARITY_INVERSED; > + state->polarity = PWM_POLARITY_NORMAL; > > return 0; > } > - Please keep this empty line between functions. > static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm, > const struct pwm_state *state) > { Best regards Uwe
Uwe Kleine-König <u.kleine-koenig@pengutronix.de> 於 2024年2月6日 週二 上午2:07寫道： > > Hello, Hi Uwe, thanks for your feedback. > > Regarding the Subject: The patch has nothing to do with an LED, has it? I will correct this. > > On Fri, Jan 26, 2024 at 03:40:44PM +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. > > Please break lines at 75 columns in the commit log. got it. > > > 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] > > I looked at Figure 29 in this document (version v1p6, pdf page 148). Not > sure I understand that correctly, but I expect that the output of the > ">=?" node below pwmcmp0 to become 1 if pwms has reached pwmcmp0, is > that right? In that case this output is zero when pwmcount is zero and > then pwmcmp0ip is zero, too. So a period starts with the inactive part > and so it's inversed polarity. > > What made you think that the current driver implementation is wrong? This is the process of my speculation. This is a HiFive Unmatched/Unleashed LED-PWM layout VDD | | _____ \ / LED \ / --- | | | ______ | | - | ^ --> |------ PWM |___|___| | | __ - GND - the waveform e.g. duty=30s, period=100s, actvie-high = 30%, active-low = 70% V ^ | | ----------| | | | | |______ |__________ > t When VCC is high, the LED will be illuminated, which is an active-high logic. This is why I want to remove "active-low". For HW, we just focus on pwmcount/pwmcmp[0-3] - pwmcount default is zero, that counter 0->1->0xffff - Follow the origin algorithm the frac=0x0(on) / 0xffff(off) and when the smaller the value of frac, the brighter the light. -- E.g. pwmcmp = 0x2, pwmcount 0x0->0x1->...->0xffff --- 0->0x2=low & 0x3->0xffff=high => 98% -- E.g. pwmcmp = 0xffff, pwmcount 0x0->0x1->...->0xffff --- 0->0xffff=low => 0% - For SW, we reference the algorithm. (D=PW/T*100% D=duty_cycle, T=period, PW=pulse width (pulse active time)) -- when we consider HW behavior --- Direct writing SW frac into HW's pwmcmp is active low, so when we want to get an active-high behavior that use a invert function. If my understanding or deduction process is incorrect, please let me know. Thank you. > > > Co-developed-by: Zong Li <zong.li@sifive.com> > > Signed-off-by: Zong Li <zong.li@sifive.com> > > Co-developed-by: Vincent Chen <vincent.chen@sifive.com> > > Signed-off-by: Vincent Chen <vincent.chen@sifive.com> > > Signed-off-by: Nylon Chen <nylon.chen@sifive.com> > > --- > > drivers/pwm/pwm-sifive.c | 7 ++++--- > > 1 file changed, 4 insertions(+), 3 deletions(-) > > > > diff --git a/drivers/pwm/pwm-sifive.c b/drivers/pwm/pwm-sifive.c > > index eabddb7c7820..b07c8598bb21 100644 > > --- a/drivers/pwm/pwm-sifive.c > > +++ b/drivers/pwm/pwm-sifive.c > > @@ -113,6 +113,7 @@ static int pwm_sifive_get_state(struct pwm_chip *chip, struct pwm_device *pwm, > > u32 duty, val; > > > > duty = readl(ddata->regs + PWM_SIFIVE_PWMCMP(pwm->hwpwm)); > > + duty = (1U << PWM_SIFIVE_CMPWIDTH) - 1 - duty; > > I find it irritating that both values are assigned to duty. I'd spend > another variable and make this: > > inactive = readl(ddata->regs + PWM_SIFIVE_PWMCMP(pwm->hwpwm)); > duty = (1U << PWM_SIFIVE_CMPWIDTH) - 1 - inactive; got it. > > > > > > state->enabled = duty > 0; > > > > @@ -123,11 +124,10 @@ static int pwm_sifive_get_state(struct pwm_chip *chip, struct pwm_device *pwm, > > state->period = ddata->real_period; > > state->duty_cycle = > > (u64)duty * ddata->real_period >> PWM_SIFIVE_CMPWIDTH; > > - state->polarity = PWM_POLARITY_INVERSED; > > + state->polarity = PWM_POLARITY_NORMAL; > > > > return 0; > > } > > - > > Please keep this empty line between functions. got it. > > > static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm, > > const struct pwm_state *state) > > { > > 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 eabddb7c7820..b07c8598bb21 100644 --- a/drivers/pwm/pwm-sifive.c +++ b/drivers/pwm/pwm-sifive.c @@ -113,6 +113,7 @@ static int pwm_sifive_get_state(struct pwm_chip *chip, struct pwm_device *pwm, u32 duty, val; duty = readl(ddata->regs + PWM_SIFIVE_PWMCMP(pwm->hwpwm)); + duty = (1U << PWM_SIFIVE_CMPWIDTH) - 1 - duty; state->enabled = duty > 0; @@ -123,11 +124,10 @@ static int pwm_sifive_get_state(struct pwm_chip *chip, struct pwm_device *pwm, state->period = ddata->real_period; state->duty_cycle = (u64)duty * ddata->real_period >> PWM_SIFIVE_CMPWIDTH; - state->polarity = PWM_POLARITY_INVERSED; + state->polarity = PWM_POLARITY_NORMAL; return 0; } - static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm, const struct pwm_state *state) { @@ -139,7 +139,7 @@ static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm, int ret = 0; u32 frac; - if (state->polarity != PWM_POLARITY_INVERSED) + if (state->polarity != PWM_POLARITY_NORMAL) return -EINVAL; cur_state = pwm->state; @@ -159,6 +159,7 @@ 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) {