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| author | Hans de Goede <hdegoede@redhat.com> | 2020-09-03 14:23:23 +0300 |
|---|---|---|
| committer | Hans de Goede <hdegoede@redhat.com> | 2020-09-06 16:37:58 +0300 |
| commit | 181f4d2f44463fe09fe4df02e03095cb87151c29 (patch) | |
| tree | 6ebda6c23394d91934c4e10bf334c6c9cdcee46b /drivers | |
| parent | 15aa5e4c4328c4060cc662105a7b4c107a072ff3 (diff) | |
| download | linux-181f4d2f44463fe09fe4df02e03095cb87151c29.tar.xz | |
pwm: lpss: Fix off by one error in base_unit math in pwm_lpss_prepare()
According to the data-sheet the way the PWM controller works is that
each input clock-cycle the base_unit gets added to a N bit counter and
that counter overflowing determines the PWM output frequency.
So assuming e.g. a 16 bit counter this means that if base_unit is set to 1,
after 65535 input clock-cycles the counter has been increased from 0 to
65535 and it will overflow on the next cycle, so it will overflow after
every 65536 clock cycles and thus the calculations done in
pwm_lpss_prepare() should use 65536 and not 65535.
This commit fixes this. Note this also aligns the calculations in
pwm_lpss_prepare() with those in pwm_lpss_get_state().
Note this effectively reverts commit 684309e5043e ("pwm: lpss: Avoid
potential overflow of base_unit"). The next patch in this series really
fixes the potential overflow of the base_unit value.
Fixes: 684309e5043e ("pwm: lpss: Avoid potential overflow of base_unit")
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200903112337.4113-4-hdegoede@redhat.com
Diffstat (limited to 'drivers')
| -rw-r--r-- | drivers/pwm/pwm-lpss.c | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/drivers/pwm/pwm-lpss.c b/drivers/pwm/pwm-lpss.c index 9d965ffe66d1..43b1fc634af1 100644 --- a/drivers/pwm/pwm-lpss.c +++ b/drivers/pwm/pwm-lpss.c @@ -93,7 +93,7 @@ static void pwm_lpss_prepare(struct pwm_lpss_chip *lpwm, struct pwm_device *pwm, * The equation is: * base_unit = round(base_unit_range * freq / c) */ - base_unit_range = BIT(lpwm->info->base_unit_bits) - 1; + base_unit_range = BIT(lpwm->info->base_unit_bits); freq *= base_unit_range; base_unit = DIV_ROUND_CLOSEST_ULL(freq, c); @@ -104,8 +104,8 @@ static void pwm_lpss_prepare(struct pwm_lpss_chip *lpwm, struct pwm_device *pwm, orig_ctrl = ctrl = pwm_lpss_read(pwm); ctrl &= ~PWM_ON_TIME_DIV_MASK; - ctrl &= ~(base_unit_range << PWM_BASE_UNIT_SHIFT); - base_unit &= base_unit_range; + ctrl &= ~((base_unit_range - 1) << PWM_BASE_UNIT_SHIFT); + base_unit &= (base_unit_range - 1); ctrl |= (u32) base_unit << PWM_BASE_UNIT_SHIFT; ctrl |= on_time_div; |