Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [PATCH 5.10 481/717] pwm: imx27: Fix overflow for bigger periods | Date | Mon, 28 Dec 2020 13:47:59 +0100 |
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From: Uwe Kleine-König <uwe@kleine-koenig.org>
[ Upstream commit 1ce65396e6b2386b4fd54f87beff0647a772e1cd ]
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 <uwe@kleine-koenig.org> Tested-by: Johannes Pointner <johannes.pointner@br-automation.com> Signed-off-by: Thierry Reding <thierry.reding@gmail.com> Signed-off-by: Sasha Levin <sashal@kernel.org> --- 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 c50d453552bd4..86bcafd23e4f6 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 -- 2.27.0
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