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

[Marcelo Tosatti]

On Fri, Mar 02, 2012 at 06:59:04AM +0000, Zhang, Yang Z wrote:
> Change DM(date mode) and 24/12 control bit don't affect the internal
> registers. It only indicates what format is using for those registers. So
> we don't need to update time format when it is modified.
> 
> Signed-off-by: Yang Zhang <address@hidden>
> ---
>  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>