rtc: mc146818-lib: extract mc146818_avoid_UIP

stable inclusion
from stable-v5.10.159
commit 33ac73a41af6ee7ab88762e09497e3d56dde6d52
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7NTXH

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=33ac73a41af6ee7ab88762e09497e3d56dde6d52



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[ Upstream commit ec5895c0 ]

Function mc146818_get_time() contains an elaborate mechanism of reading
the RTC time while no RTC update is in progress. It turns out that
reading the RTC alarm clock also requires avoiding the RTC update.
Therefore, the mechanism in mc146818_get_time() should be reused - so
extract it into a separate function.

The logic in mc146818_avoid_UIP() is same as in mc146818_get_time()
except that after every

        if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP) {

there is now "mdelay(1)".

To avoid producing a very unreadable patch, mc146818_get_time() will be
refactored to use mc146818_avoid_UIP() in the next patch.

Signed-off-by: Mateusz Jończyk <mat.jonczyk@o2.pl>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20211210200131.153887-6-mat.jonczyk@o2.pl


Stable-dep-of: cd17420e ("rtc: cmos: avoid UIP when writing alarm time")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: sanglipeng <sanglipeng1@jd.com>