diff options
| author | Uwe Kleine-König <u.kleine-koenig@pengutronix.de> | 2021-01-15 10:32:39 +0300 |
|---|---|---|
| committer | Thierry Reding <thierry.reding@gmail.com> | 2021-02-22 17:18:36 +0300 |
| commit | 72d6b2459dbd539c1369149e501fdc3dc8ddef16 (patch) | |
| tree | 31546bd1adaf63df7e85f393ecf55b59468c7dee /drivers/pwm | |
| parent | 11be938ae003c1cf157f0e80d5c9ad29a0f4c34c (diff) | |
| download | linux-72d6b2459dbd539c1369149e501fdc3dc8ddef16.tar.xz | |
pwm: iqs620a: Fix overflow and optimize calculations
If state->duty_cycle is 0x100000000000000, the previous calculation of
duty_scale overflows and yields a duty cycle ratio of 0% instead of
100%. Fix this by clamping the requested duty cycle to the maximal
possible duty cycle first. This way it is possible to use a native
integer division instead of a (depending on the architecture) more
expensive 64bit division.
With this change in place duty_scale cannot be bigger than 256 which
allows to simplify the calculation of duty_val.
Fixes: 6f0841a8197b ("pwm: Add support for Azoteq IQS620A PWM generator")
Tested-by: Jeff LaBundy <jeff@labundy.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
Diffstat (limited to 'drivers/pwm')
| -rw-r--r-- | drivers/pwm/pwm-iqs620a.c | 8 |
1 files changed, 5 insertions, 3 deletions
diff --git a/drivers/pwm/pwm-iqs620a.c b/drivers/pwm/pwm-iqs620a.c index 5ede8255926e..14b18fb4f527 100644 --- a/drivers/pwm/pwm-iqs620a.c +++ b/drivers/pwm/pwm-iqs620a.c @@ -46,7 +46,8 @@ static int iqs620_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, { struct iqs620_pwm_private *iqs620_pwm; struct iqs62x_core *iqs62x; - u64 duty_scale; + unsigned int duty_cycle; + unsigned int duty_scale; int ret; if (state->polarity != PWM_POLARITY_NORMAL) @@ -70,7 +71,8 @@ static int iqs620_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, * For lower duty cycles (e.g. 0), the PWM output is simply disabled to * allow an external pull-down resistor to hold the GPIO3/LTX pin low. */ - duty_scale = div_u64(state->duty_cycle * 256, IQS620_PWM_PERIOD_NS); + duty_cycle = min_t(u64, state->duty_cycle, IQS620_PWM_PERIOD_NS); + duty_scale = duty_cycle * 256 / IQS620_PWM_PERIOD_NS; mutex_lock(&iqs620_pwm->lock); @@ -82,7 +84,7 @@ static int iqs620_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, } if (duty_scale) { - u8 duty_val = min_t(u64, duty_scale - 1, 0xff); + u8 duty_val = duty_scale - 1; ret = regmap_write(iqs62x->regmap, IQS620_PWM_DUTY_CYCLE, duty_val); |