On 24/09/2019 10:41:08+0800, Jinke Fan wrote: > When using following operations: > date -s "21190910 19:20:00" > hwclock -w > to change date from 2019 to 2119 for test, it will fail on Hygon > Dhyana and AMD Zen CPUs, while the same operations run ok on Intel i7 > platform. > > MC146818 driver use function mc146818_set_time() to set register > RTC_FREQ_SELECT(RTC_REG_A)'s bit4-bit6 field which means divider stage > reset value on Intel platform to 0x7. > > While AMD/Hygon RTC_REG_A(0Ah)'s bit4 is defined as DV0 [Reference]: > DV0 = 0 selects Bank 0, DV0 = 1 selects Bank 1. Bit5-bit6 is defined > as reserved. > > DV0 is set to 1, it will select Bank 1, which will disable AltCentury > register(0x32) access. As UEFI pass acpi_gbl_FADT.century 0x32 > (AltCentury), the CMOS write will be failed on code: > CMOS_WRITE(century, acpi_gbl_FADT.century). > > Correct RTC_REG_A bank select bit(DV0) to 0 on AMD/Hygon CPUs, it will > enable AltCentury(0x32) register writing and finally setup century as > expected. > > Test results on AMD/Hygon machine show that it works as expected. > > Reference: > https://www.amd.com/system/files/TechDocs/51192_Bolton_FCH_RRG.pdf > section: 3.13 Real Time Clock (RTC) > > Signed-off-by: Jinke Fan <fanjinke@xxxxxxxx> > --- > drivers/rtc/rtc-mc146818-lib.c | 9 +++++++-- > include/linux/mc146818rtc.h | 2 ++ > 2 files changed, 9 insertions(+), 2 deletions(-) > Applied, thanks. -- Alexandre Belloni, Bootlin Embedded Linux and Kernel engineering https://bootlin.com