Re: [Qemu-devel] [PATCH v3 1/7] RTC: Remove the logic to update time format when DM bit changed

[Zhang, Yang Z]

> -----Original Message-----
> From: Marcelo Tosatti [mailto:address@hidden
> Sent: Friday, March 09, 2012 9:36 AM
> > ---
> >  hw/mc146818rtc.c |   10 +---------
> >  1 files changed, 1 insertions(+), 9 deletions(-)
> >
> > diff --git a/hw/mc146818rtc.c b/hw/mc146818rtc.c
> > index a46fdfc..9b49cbc 100644
> > --- a/hw/mc146818rtc.c
> > +++ b/hw/mc146818rtc.c
> > @@ -252,15 +252,7 @@ static void cmos_ioport_write(void *opaque, uint32_t
> addr, uint32_t data)
> >                      rtc_set_time(s);
> >                  }
> >              }
> > -            if (((s->cmos_data[RTC_REG_B] ^ data) & (REG_B_DM |
> REG_B_24H)) &&
> > -                !(data & REG_B_SET)) {
> > -                /* If the time format has changed and not in set mode,
> > -                   update the registers immediately. */
> > -                s->cmos_data[RTC_REG_B] = data;
> > -                rtc_copy_date(s);
> > -            } else {
> > -                s->cmos_data[RTC_REG_B] = data;
> > -            }
> > +            s->cmos_data[RTC_REG_B] = data;
> >              rtc_timer_update(s, qemu_get_clock_ns(rtc_clock));
> >              break;
> >          case RTC_REG_C:
> 
> Even though its not correct accordingly to the manual, guests can update
> format and expect it to be reflected to time byte reads.
> 
> commit 51e08f3e4b8a3b6d27fde9a9e75c8fa32eaa72d0
> Author: Aurelien Jarno <address@hidden>
> Date:   Tue Jan 25 11:55:15 2011 +0100
> 
> mc146818rtc: update registers after a format change
> 
> For some unknown reason, the MIPS kernel briefly changes the RTC to
> binary mode during boot, switch back to BCD mode and read the time. As
> the registers are updated only every second, they may still be in the
> old format when they are read.
> 
> This patch forces a register update immediately after a format
> change (BCD/binary or 12/24H). This avoid long fsck during boot due to
> time wrap.
> 
> Signed-off-by: Aurelien Jarno <address@hidden>
> 
This is obvious a wrong fixing. Even for real RTC, changing date mode will not 
change the internal time register. So the MIPS kernel also should not boot up 
with real RTC. But it only fail in qemu, this means he not found the culprit. 
This just a workaround.


best regards
yang