rtc: cmos: avoid UIP when reading alarm time
Some Intel chipsets disconnect the time and date RTC registers when the clock update is in progress: during this time reads may return bogus values and writes fail silently. This includes the RTC alarm registers. [1] cmos_read_alarm() did not take account for that, which caused alarm time reads to sometimes return bogus values. This can be shown with a test patch that I am attaching to this patch series. Fix this, by using mc146818_avoid_UIP(). [1] 7th Generation Intel ® Processor Family I/O for U/Y Platforms [...] Datasheet, Volume 1 of 2 (Intel's Document Number: 334658-006) Page 208 https://www.intel.com/content/dam/www/public/us/en/documents/datasheets/7th-and-8th-gen-core-family-mobile-u-y-processor-lines-i-o-datasheet-vol-1.pdf "If a RAM read from the ten time and date bytes is attempted during an update cycle, the value read do not necessarily represent the true contents of those locations. Any RAM writes under the same conditions are ignored." 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:
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