Messages in this thread Patch in this message | | | From | Fabrice Gasnier <> | Subject | [PATCH v2] pwm: stm32-lp: add check in case requested period cannot be achieved | Date | Wed, 18 Sep 2019 16:54:21 +0200 |
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LPTimer can use a 32KHz clock for counting. It depends on clock tree configuration. In such a case, PWM output frequency range is limited. Although unlikely, nothing prevents user from requesting a PWM frequency above counting clock (32KHz for instance): - This causes (prd - 1) = 0xffff to be written in ARR register later in the apply() routine. This results in badly configured PWM period (and also duty_cycle). Add a check to report an error is such a case.
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com> --- Changes in v2: - remarks from Uwe: update the comment, use dev_dbg() and print period that cannot be reached --- drivers/pwm/pwm-stm32-lp.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/drivers/pwm/pwm-stm32-lp.c b/drivers/pwm/pwm-stm32-lp.c index 2211a64..97a9afa 100644 --- a/drivers/pwm/pwm-stm32-lp.c +++ b/drivers/pwm/pwm-stm32-lp.c @@ -59,6 +59,12 @@ static int stm32_pwm_lp_apply(struct pwm_chip *chip, struct pwm_device *pwm, /* Calculate the period and prescaler value */ div = (unsigned long long)clk_get_rate(priv->clk) * state->period; do_div(div, NSEC_PER_SEC); + if (!div) { + /* Clock is too slow to achieve requested period. */ + dev_dbg(priv->chip.dev, "Can't reach %u ns\n", state->period); + return -EINVAL; + } + prd = div; while (div > STM32_LPTIM_MAX_ARR) { presc++; -- 2.7.4
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