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Max Kellermann authored
This fixes a problem that was supposed to be addressed by commit 6eefb79d ("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>
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