Re: [edk2-devel] [PATCH] PcAtChipsetPkg: Wrong System YEAR displayed in SETUP

["Ni, Ray" <ray.ni@intel.com>]

Lijian,
Yeah. I might learn the CMOS/RTC from the same page you shared when I create the two PCDs and the accordingly logic.
Just guess as what the page says.

I double checked the existing code.
RtcTimeFieldsValid() contains logic to check all date/time value read from
RTC HW and PcRtcInit() re-inits the RTC HW if date/time in HW is invalid.

Thanks,
Ray

> -----Original Message-----
> From: Zhao, Lijian <lijian.zhao@intel.com>
> Sent: Thursday, May 14, 2020 1:56 PM
> To: Ni, Ray <ray.ni@intel.com>; Yau, KaiX <kaix.yau@intel.com>; devel@edk2.groups.io; kaiyau@gmail.com
> Cc: Jiang, Guomin <guomin.jiang@intel.com>; Gao, Liming <liming.gao@intel.com>; Archield, Ralphal
> <ralphal.archield@intel.com>
> Subject: RE: [edk2-devel] [PATCH] PcAtChipsetPkg: Wrong System YEAR displayed in SETUP
> 
> https://wiki.osdev.org/CMOS#Century_Register
> 
> Yes that's not fixed or defined in original IBM standard
> 
> -----Original Message-----
> From: Ni, Ray <ray.ni@intel.com>
> Sent: Thursday, May 14, 2020 1:38 PM
> To: Yau, KaiX <kaix.yau@intel.com>; devel@edk2.groups.io; kaiyau@gmail.com
> Cc: Jiang, Guomin <guomin.jiang@intel.com>; Gao, Liming <liming.gao@intel.com>; Archield, Ralphal
> <ralphal.archield@intel.com>; Zhao, Lijian <lijian.zhao@intel.com>
> Subject: RE: [edk2-devel] [PATCH] PcAtChipsetPkg: Wrong System YEAR displayed in SETUP
> 
> Kai,
> Thanks for telling me the commit message can help understand.
> 
> RTC HW updates the year/month/day/hour/minute/second every second.
> But the year stored in RTC is only the last two digits of the 4-digit year.
> 
> Storing the century (high 2 digits) in CMOS is a choice of platform implementation and cannot work for all the cases.
> 
> Supposing now we are in the last second of 2099, RTC HW updates the value in RTC to
> 00(year)/1(month)/1(day)/0(hour)/0(minute)/0(second). But it doesn't update the century value in CMOS leaving that
> value 20.
> Then the time will be interpreted as 2000/1/1/0/0/0.
> 
> That's why RTC driver only updates the century in CMOS when platform reports the century location through the FADT
> table. Please understand RTC driver updates it because platform requires it (through reporting CMOS location in FADT.).
> 
> Please also try to understand that the location of century in CMOS is platform dependent.
> There is no standard to define location for all x86 systems.
> 
> Thanks,
> Ray
> 
> > -----Original Message-----
> > From: Yau, KaiX <kaix.yau@intel.com>
> > Sent: Thursday, May 14, 2020 11:36 AM
> > To: Ni, Ray <ray.ni@intel.com>; devel@edk2.groups.io; kaiyau@gmail.com
> > Cc: Jiang, Guomin <guomin.jiang@intel.com>; Gao, Liming
> > <liming.gao@intel.com>; Archield, Ralphal
> > <ralphal.archield@intel.com>; Zhao, Lijian <lijian.zhao@intel.com>
> > Subject: RE: [edk2-devel] [PATCH] PcAtChipsetPkg: Wrong System YEAR
> > displayed in SETUP
> >
> > Hi Ray,
> >
> > I read your comment from gitk.
> > I understand why you changed them to 1998 and 2097.
> >
> > May I know why we don't read the Century value from CMOS in the beginning?
> >     Some boards does not support? Or the RTC address may be different for different boards?
> >
> > Regards
> > Kai Yau
> >
> > -----Original Message-----
> > From: Ni, Ray <ray.ni@intel.com>
> > Sent: Wednesday, May 13, 2020 10:55 PM
> > To: Yau, KaiX <kaix.yau@intel.com>; devel@edk2.groups.io;
> > kaiyau@gmail.com
> > Cc: Jiang, Guomin <guomin.jiang@intel.com>; Gao, Liming
> > <liming.gao@intel.com>; Archield, Ralphal
> > <ralphal.archield@intel.com>; Zhao, Lijian <lijian.zhao@intel.com>
> > Subject: RE: [edk2-devel] [PATCH] PcAtChipsetPkg: Wrong System YEAR
> > displayed in SETUP
> >
> > Kai,
> > I created the initial design and made the initial change: using the two PCD to help code decide the correct century value.
> > More comments below.
> >
> > > -----Original Message-----
> > > From: Yau, KaiX <kaix.yau@intel.com>
> > > Sent: Thursday, May 14, 2020 1:14 AM
> > > To: Ni, Ray <ray.ni@intel.com>; devel@edk2.groups.io;
> > > kaiyau@gmail.com
> > > Cc: Jiang, Guomin <guomin.jiang@intel.com>; Gao, Liming
> > > <liming.gao@intel.com>; Archield, Ralphal
> > > <ralphal.archield@intel.com>; Zhao, Lijian <lijian.zhao@intel.com>
> > > Subject: RE: [edk2-devel] [PATCH] PcAtChipsetPkg: Wrong System YEAR
> > > displayed in SETUP
> > >
> > > Hi,
> > >
> > > The current logic has two limitations:
> > > 1. it has to be 100 years apart  (already mentioned in DEC file)
> > I agree it's a limitation. I don't want to solve this limitation with current RTC HW.
> >
> > > 2. the century numbers have to be same in order to work. (19XX, 20XX
> > > will not work) (20xx, 21xx will not work) Since now is 2020, the
> > > value has to be 2000, 2099. But BIOS developers does not
> > know this limitation.
> > I don't agree. Let's forget other argue points and just focus on this point.
> > Can you please explain why with the PCD value (1998,2097) cannot support this year 2020?
> 
>