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[Xen-devel] [PATCH] x86: Don't honour ACPI indicating absence of CMOS RTC

This reverts f74556693 "x86: honor ACPI indicating absence of CMOS RTC"

Certain HP Gen8 BIOSes have started setting this bit despite an RTC CMOS being
present and working.

Their reasonsing is to prevent EFI-booted OSes from playing with the CMOS,
combined with the erroneous assumption that the only OSes using legacy boot
are too old to know about ACPI v5 and therefore to understand this bit.

As a result, the change being reverted prevented modern Xen from booting on
modern HP hardware, despite older Xen working perfectly fine on the same

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: Keir Fraser <keir@xxxxxxx>
CC: Jan Beulich <JBeulich@xxxxxxxx>
 xen/arch/x86/time.c |    3 ---
 1 file changed, 3 deletions(-)

diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
index a4e1656..8745186 100644
--- a/xen/arch/x86/time.c
+++ b/xen/arch/x86/time.c
@@ -693,9 +693,6 @@ static unsigned long get_cmos_time(void)
             return res;
-    if ( unlikely(acpi_gbl_FADT.boot_flags & ACPI_FADT_NO_CMOS_RTC) )
-        panic("System without CMOS RTC must be booted from EFI");
     spin_lock_irqsave(&rtc_lock, flags);
     /* read RTC exactly on falling edge of update flag */

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