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Subject[PATCH] pwm: stm32-lp: add check in case requested period cannot be achieved
Date
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>
---
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..5c2c728 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) {
+ /* Fall here in case source clock < period */
+ dev_err(priv->chip.dev, "Can't reach expected period\n");
+ return -EINVAL;
+ }
+
prd = div;
while (div > STM32_LPTIM_MAX_ARR) {
presc++;
--
2.7.4
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