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Re: [PATCH for-4.22 1/5] x86/time: use RTC century byte when available
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Wed, 13 May 2026 10:49:11 +0200
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Teddy Astie <teddy.astie@xxxxxxxxxx>, Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
- Delivery-date: Wed, 13 May 2026 08:49:26 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Tue, May 12, 2026 at 04:58:43PM +0200, Jan Beulich wrote:
> Without this the present logic will misbehave from 2070 onwards.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>
> --- a/xen/arch/x86/time.c
> +++ b/xen/arch/x86/time.c
> @@ -1257,6 +1257,7 @@ struct rtc_time {
> static bool __get_cmos_time(struct rtc_time *rtc)
> {
> s_time_t start, t1, t2;
> + unsigned int century = 0;
> unsigned long flags;
>
> spin_lock_irqsave(&rtc_lock, flags);
> @@ -1280,6 +1281,8 @@ static bool __get_cmos_time(struct rtc_t
> rtc->day = CMOS_READ(RTC_DAY_OF_MONTH);
> rtc->mon = CMOS_READ(RTC_MONTH);
> rtc->year = CMOS_READ(RTC_YEAR);
> + if ( acpi_gbl_FADT.century && acpi_gbl_FADT.century < 0x80 )
> + century = CMOS_READ(acpi_gbl_FADT.century);
>
> if ( RTC_ALWAYS_BCD || !(CMOS_READ(RTC_CONTROL) & RTC_DM_BINARY) )
> {
> @@ -1293,7 +1296,12 @@ static bool __get_cmos_time(struct rtc_t
>
> spin_unlock_irqrestore(&rtc_lock, flags);
>
> - if ( (rtc->year += 1900) < 1970 )
> + if ( century )
> + {
> + BCD_TO_BIN(century);
Don't you need to move the BCD_TO_BIN() translation with the rest, so
it's not done unconditionally?
Thanks, Roger.
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