From: Fabrice Gasnier <fabrice.gasnier@st.com>
To: <thierry.reding@gmail.com>
Cc: <fabrice.gasnier@st.com>, <alexandre.torgue@st.com>,
<mcoquelin.stm32@gmail.com>, <linux-pwm@vger.kernel.org>,
<linux-arm-kernel@lists.infradead.org>,
<linux-kernel@vger.kernel.org>
Subject: [PATCH] pwm: stm32-lp: add check in case requested period cannot be achieved
Date: Tue, 17 Sep 2019 15:51:50 +0200 [thread overview]
Message-ID: <1568728310-20948-1-git-send-email-fabrice.gasnier@st.com> (raw)
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
next reply other threads:[~2019-09-17 13:53 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-17 13:51 Fabrice Gasnier [this message]
2019-09-17 20:28 ` [PATCH] pwm: stm32-lp: add check in case requested period cannot be achieved Uwe Kleine-König
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