From 1ce65396e6b2386b4fd54f87beff0647a772e1cd Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Uwe=20Kleine-K=C3=B6nig?= Date: Mon, 7 Dec 2020 15:13:24 +0100 Subject: [PATCH] pwm: imx27: Fix overflow for bigger periods MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The second parameter of do_div is an u32 and NSEC_PER_SEC * prescale overflows this for bigger periods. Assuming the usual pwm input clk rate of 66 MHz this happens starting at requested period > 606060 ns. Splitting the division into two operations doesn't loose any precision. It doesn't need to be feared that c / NSEC_PER_SEC doesn't fit into the unsigned long variable "duty_cycles" because in this case the assignment above to period_cycles would already have been overflowing as period >= duty_cycle and then the calculation is moot anyhow. Fixes: aef1a3799b5c ("pwm: imx27: Fix rounding behavior") Signed-off-by: Uwe Kleine-König Tested-by: Johannes Pointner Signed-off-by: Thierry Reding --- drivers/pwm/pwm-imx27.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/pwm/pwm-imx27.c b/drivers/pwm/pwm-imx27.c index ceaed0378de7..18055326a2f3 100644 --- a/drivers/pwm/pwm-imx27.c +++ b/drivers/pwm/pwm-imx27.c @@ -235,8 +235,9 @@ static int pwm_imx27_apply(struct pwm_chip *chip, struct pwm_device *pwm, period_cycles /= prescale; c = clkrate * state->duty_cycle; - do_div(c, NSEC_PER_SEC * prescale); + do_div(c, NSEC_PER_SEC); duty_cycles = c; + duty_cycles /= prescale; /* * according to imx pwm RM, the real period value should be PERIOD