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| author | Uwe Kleine-König <uwe@kleine-koenig.org> | 2020-12-07 15:13:24 +0100 |
|---|---|---|
| committer | Thierry Reding <thierry.reding@gmail.com> | 2020-12-17 14:19:01 +0100 |
| commit | 1ce65396e6b2386b4fd54f87beff0647a772e1cd (patch) | |
| tree | cca99627399743fa0652c4a2186c20d80e7c7639 /drivers/pwm/pwm-imx27.c | |
| parent | 2f81b51d0d02074502ad27424c228ca760823668 (diff) | |
| download | linux-stable-1ce65396e6b2386b4fd54f87beff0647a772e1cd.tar.gz linux-stable-1ce65396e6b2386b4fd54f87beff0647a772e1cd.tar.bz2 linux-stable-1ce65396e6b2386b4fd54f87beff0647a772e1cd.zip | |
pwm: imx27: Fix overflow for bigger periods
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>
Diffstat (limited to 'drivers/pwm/pwm-imx27.c')
| -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 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 |