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authorMax Kellermann <max.kellermann@gmail.com>2022-01-25 15:34:29 +0300
committerThierry Reding <thierry.reding@gmail.com>2022-04-22 18:44:48 +0300
commit8246b478a23aafdef0e1deb2ac2f21eeee97e877 (patch)
tree502f90f5d6f2f9e31ad4c864525f75caf166c43f /drivers/pwm
parentba3e5037ceeb920e98970e2342edd7ab390217c0 (diff)
downloadlinux-8246b478a23aafdef0e1deb2ac2f21eeee97e877.tar.xz
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.c4
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