diff options
| author | Uwe Kleine-König <uwe@kleine-koenig.org> | 2020-12-07 15:13:24 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2020-12-30 11:53:59 +0100 |
| commit | 7c4544a216e34c3867429585e532bec540c99751 (patch) | |
| tree | b1e9e0afd22f1f7d5de8fb1988f9507aca42d344 /drivers/pwm | |
| parent | 2cacf60c924521b99d9c0fafe63f128ddc191b6b (diff) | |
pwm: imx27: Fix overflow for bigger periods
[ 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>
Diffstat (limited to 'drivers/pwm')
| -rw-r--r-- | drivers/pwm/pwm-imx27.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/drivers/pwm/pwm-imx27.c b/drivers/pwm/pwm-imx27.c index c50d453552bd..86bcafd23e4f 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 |