Re: [PATCH] Revert "iee1275/datetime: Fix off-by-1 error."

[Glenn Washburn]

On Tue, 08 Feb 2022 15:51:41 +1100
Daniel Axtens <dja@axtens.net> wrote:

> Hi,
> 
> I tested a pseries guest under:
>  - qemu + KVM on a Power8 host with a fairly modern qemu
>  - qemu + TCG
> 
> Here the 'date' command simply reports "error: no cmos found", so
> this patch will have no impact on those platforms.

I suspect its the same on KVM and TCG because the machine definition is
the same and doesn't container either an RTC nor a CMOS. What confusing
to me is, don't these machines have clocks?

> 
> I also tested an LPAR on a Power8 PowerVM machine. In this case, before
> the patch, grub printed:
> 
> grub> date
> 2022-02-09 04:31:10 Wednesday
> 
> whereas on booting:
> 
> [dja@sauce ~]$ date -u
> Tue Feb  8 04:46:40 UTC 2022
> 
> After applying the patch, grub printed:
> 
> grub> date
> 2022-02-08 04:51:27 Tuesday
> 
> It seems the patch makes things better.

Great thanks Daniel for confirming this.

Glenn

> 
> Tested-by: Daniel Axtens <dja@axtens.net>
> 
> Kind regards,
> Daniel
> 
> Glenn Washburn <development@efficientek.com> writes:
> 
> > This is causing the test grub_cmd_date to fail because the returned date is
> > one day more than it should be.
> >
> > This reverts commit 607d66116a67e5a13eb0d46076f26dedc988e6a4.
> >
> > Signed-off-by: Glenn Washburn <development@efficientek.com>
> > ---
> > Hi all,
> >
> > Reverting this commit allows the grub_cmd_date test to pass. It appears that
> > this commit is (now) causing an off-by-1 error in QEMU and the latest 
> > OpenBIOS.
> > What I'm unsure of is if the original commit is actually correct on real
> > hardware and that potentially OpenBIOS has a bug.
> >
> > Adrian and Daniel A, could you test the reverting of this commit on real
> > hardware and see if date does in fact produce the expected date (and do 
> > current
> > builds show a date one day ahead of what it should be)? Can anyone point to
> > documentation saying that the original commit is in fact what should
> > be done? If the issue is in OpenBIOS I'd like to have some documentation
> > to back up a bug report.
> >
> > Vladimir, do you have any thoughts on this?
> >
> > Glenn
> >
> > ---
> >  grub-core/lib/ieee1275/datetime.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/grub-core/lib/ieee1275/datetime.c 
> > b/grub-core/lib/ieee1275/datetime.c
> > index b81fba2ed..74578f15a 100644
> > --- a/grub-core/lib/ieee1275/datetime.c
> > +++ b/grub-core/lib/ieee1275/datetime.c
> > @@ -95,7 +95,7 @@ grub_get_datetime (struct grub_datetime *datetime)
> >  
> >    datetime->year = args.year;
> >    datetime->month = args.month;
> > -  datetime->day = args.day + 1;
> > +  datetime->day = args.day;
> >    datetime->hour = args.hour;
> >    datetime->minute = args.minute;
> >    datetime->second = args.second;
> > @@ -140,7 +140,7 @@ grub_set_datetime (struct grub_datetime *datetime)
> >  
> >    args.year = datetime->year;
> >    args.month = datetime->month;
> > -  args.day = datetime->day - 1;
> > +  args.day = datetime->day;
> >    args.hour = datetime->hour;
> >    args.minute = datetime->minute;
> >    args.second = datetime->second;
> > -- 
> > 2.27.0