From: Uwe Kleine-König Date: Wed, 15 Apr 2026 14:50:12 +0000 (+0200) Subject: pwm: stm32: Fix rounding issue for requests with inverted polarity X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=5d087c485b6ecf200a9ebb2a032bf8571d330250;p=thirdparty%2Fkernel%2Fstable.git pwm: stm32: Fix rounding issue for requests with inverted polarity The calculation of the number of pwm clk ticks from a time length in nanoseconds involves a division and thus some rounding. That might result in duty_ticks + offset_ticks < period_ticks despite duty_length_ns + duty_offset_ns >= period_length_ns . The stm32 PWM cannot configure offset_ticks freely, it can only select 0 or period_length_ns - duty_length_ns---that is the classic normal and inverted polarity. The decision to select the hardware polarity must be done using the ticks values and not the nanoseconds times to adhere to the rounding rules by the pwm core. With the pwm clk running at 208900 kHz on my test machine (stm32mp135f-dk), a test case that was handled wrong is: # pwmround -P 9999962 -O 24970 -D 9974992 period_length = 9999962 duty_length = 9974840 duty_offset = 25123 With this change applied the rounding is done correctly: # pwmround -P 9999962 -O 24970 -D 9974992 period_length = 9999962 duty_length = 9974840 duty_offset = 0 Fixes: deaba9cff809 ("pwm: stm32: Implementation of the waveform callbacks") Signed-off-by: Uwe Kleine-König Link: https://patch.msgid.link/c5e7767cee821b5f6e00f95bd14a5e13015646fb.1776264104.git.u.kleine-koenig@baylibre.com Signed-off-by: Uwe Kleine-König --- diff --git a/drivers/pwm/pwm-stm32.c b/drivers/pwm/pwm-stm32.c index 2594fb771b04..935257a890b0 100644 --- a/drivers/pwm/pwm-stm32.c +++ b/drivers/pwm/pwm-stm32.c @@ -68,7 +68,7 @@ static int stm32_pwm_round_waveform_tohw(struct pwm_chip *chip, struct stm32_pwm *priv = to_stm32_pwm_dev(chip); unsigned int ch = pwm->hwpwm; unsigned long rate; - u64 ccr, duty; + u64 duty_ticks, offset_ticks; int ret; if (wf->period_length_ns == 0) { @@ -164,23 +164,25 @@ static int stm32_pwm_round_waveform_tohw(struct pwm_chip *chip, wfhw->arr = min_t(u64, arr, priv->max_arr) - 1; } - duty = mul_u64_u64_div_u64(wf->duty_length_ns, rate, - (u64)NSEC_PER_SEC * (wfhw->psc + 1)); - duty = min_t(u64, duty, wfhw->arr + 1); + duty_ticks = mul_u64_u64_div_u64(wf->duty_length_ns, rate, + (u64)NSEC_PER_SEC * (wfhw->psc + 1)); + duty_ticks = min_t(u64, duty_ticks, wfhw->arr + 1); - if (wf->duty_length_ns && wf->duty_offset_ns && - wf->duty_length_ns + wf->duty_offset_ns >= wf->period_length_ns) { + offset_ticks = mul_u64_u64_div_u64(wf->duty_offset_ns, rate, + (u64)NSEC_PER_SEC * (wfhw->psc + 1)); + offset_ticks = min_t(u64, offset_ticks, wfhw->arr + 1); + + if (duty_ticks && offset_ticks && + duty_ticks + offset_ticks >= wfhw->arr + 1) { wfhw->ccer |= TIM_CCER_CCxP(ch + 1); if (priv->have_complementary_output) wfhw->ccer |= TIM_CCER_CCxNP(ch + 1); - ccr = wfhw->arr + 1 - duty; + wfhw->ccr = wfhw->arr + 1 - duty_ticks; } else { - ccr = duty; + wfhw->ccr = duty_ticks; } - wfhw->ccr = min_t(u64, ccr, wfhw->arr + 1); - out: dev_dbg(&chip->dev, "pwm#%u: %lld/%lld [+%lld] @%lu -> CCER: %08x, PSC: %08x, ARR: %08x, CCR: %08x\n", pwm->hwpwm, wf->duty_length_ns, wf->period_length_ns, wf->duty_offset_ns,