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| author |   Max Kellermann <max.kellermann@gmail.com> | 2022-01-25 13:34:29 +0100 |
|---|---|---|
| committer |   Thierry Reding <thierry.reding@gmail.com> | 2022-04-22 17:44:48 +0200 |
| commit | 8246b478a23aafdef0e1deb2ac2f21eeee97e877 (patch) | |
| tree | 502f90f5d6f2f9e31ad4c864525f75caf166c43f /drivers/pwm | |
| parent | pwm-sun4i: Calculate "delay_jiffies" directly, eliminate absolute time (diff) | |
| download | linux-dev-8246b478a23aafdef0e1deb2ac2f21eeee97e877.tar.xz linux-dev-8246b478a23aafdef0e1deb2ac2f21eeee97e877.zip | |
pwm-sun4i: Calculate the delay without rounding down to jiffies
This fixes a problem that was supposed to be addressed by commit
6eefb79d6f5bc ("pwm: sun4i: Remove erroneous else branch") - backlight
could not be switched off on some Allwinner A20. The commit was
correct, but was not a reliable fix for the problem, which was timing
related.
The real problem for the backlight switching problem was that sleeping
for a full period did not work, because delay_us is always zero.
It is zero because the period (plus 1 microsecond) is rounded down to
the next "jiffies", but the period is less than one jiffy.
On my Cubieboard 2, the period is 5ms, and 1 jiffy (at the default
HZ=100) is 10ms, so nsecs_to_jiffies(10ms+1us)=0.
The roundtrip from nanoseconds to jiffies and back to microseconds is
an unnecessary loss of precision; always rounding down (via
nsecs_to_jiffies()) then causes the breakage.
This patch eliminates this roundtrip, and directly converts from
nanoseconds to microseconds (for usleep_range()), using
DIV_ROUND_UP_ULL() to force rounding up. This way, the sleep time is
never zero, and after the sleep, we are guaranteed to be in a
different period, and the device is ready for another control command
for sure.
Signed-off-by: Max Kellermann <max.kellermann@gmail.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
Diffstat (limited to 'drivers/pwm')
| -rw-r--r-- | drivers/pwm/pwm-sun4i.c | 4 |
1 files changed, 1 insertions, 3 deletions
diff --git a/drivers/pwm/pwm-sun4i.c b/drivers/pwm/pwm-sun4i.c index 9134db4f52a9..c8445b0a3339 100644 --- a/drivers/pwm/pwm-sun4i.c +++ b/drivers/pwm/pwm-sun4i.c @@ -234,7 +234,6 @@ static int sun4i_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, struct pwm_state cstate; u32 ctrl, duty = 0, period = 0, val; int ret; - unsigned int delay_jiffies; unsigned int delay_us, prescaler = 0; bool bypass; @@ -302,8 +301,7 @@ static int sun4i_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, return 0; /* We need a full period to elapse before disabling the channel. */ - delay_jiffies = nsecs_to_jiffies(cstate.period + 1000); - delay_us = jiffies_to_usecs(delay_jiffies); + delay_us = DIV_ROUND_UP_ULL(cstate.period, NSEC_PER_USEC); if ((delay_us / 500) > MAX_UDELAY_MS) msleep(delay_us / 1000 + 1); else |