* [PATCH] pwm: stm32-lp: add check in case requested period cannot be achieved
@ 2019-09-17 13:51 Fabrice Gasnier
2019-09-17 20:28 ` Uwe Kleine-König
0 siblings, 1 reply; 2+ messages in thread
From: Fabrice Gasnier @ 2019-09-17 13:51 UTC (permalink / raw)
To: thierry.reding
Cc: fabrice.gasnier, alexandre.torgue, mcoquelin.stm32, linux-pwm,
linux-arm-kernel, linux-kernel
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
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] pwm: stm32-lp: add check in case requested period cannot be achieved
2019-09-17 13:51 [PATCH] pwm: stm32-lp: add check in case requested period cannot be achieved Fabrice Gasnier
@ 2019-09-17 20:28 ` Uwe Kleine-König
0 siblings, 0 replies; 2+ messages in thread
From: Uwe Kleine-König @ 2019-09-17 20:28 UTC (permalink / raw)
To: Fabrice Gasnier
Cc: thierry.reding, alexandre.torgue, mcoquelin.stm32, linux-pwm,
linux-arm-kernel, linux-kernel
On Tue, Sep 17, 2019 at 03:51:50PM +0200, Fabrice Gasnier wrote:
> 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 */
Does "clock < period" make sense? I'd just write: "Clock is too slow to
achieve period."
> + dev_err(priv->chip.dev, "Can't reach expected period\n");
IMHO this is little helpful. If a consumer requests such an
unsatisfiable state several times your log is spammed and you don't even
see the what was requested. I'd drop the message completely (or make it
a dev_debug).
> + return -EINVAL;
> + }
> +
> prd = div;
> while (div > STM32_LPTIM_MAX_ARR) {
> presc++;
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |
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