This is a note to let you know that I've just added the patch titled pwm: iqs620a: Fix overflow and optimize calculations to the 5.11-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: pwm-iqs620a-fix-overflow-and-optimize-calculations.patch and it can be found in the queue-5.11 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit ff0acafa79eda7cd09e93d9bdd980bf656dd8ec3 Author: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx> Date: Fri Jan 15 08:32:39 2021 +0100 pwm: iqs620a: Fix overflow and optimize calculations [ Upstream commit 72d6b2459dbd539c1369149e501fdc3dc8ddef16 ] 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@xxxxxxxxxxx> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx> Signed-off-by: Thierry Reding <thierry.reding@xxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/drivers/pwm/pwm-iqs620a.c b/drivers/pwm/pwm-iqs620a.c index 5ede8255926ef..14b18fb4f5274 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);