Re: [Qemu-devel] [PATCH] hw/i386: fill in the CENTURY field of the FADT (FACP) ACPI table

[Igor Mammedov]

On Thu, 10 Dec 2015 18:25:34 +0100
Laszlo Ersek <address@hidden> wrote:

> The ACPI specification (minimally versions 1.0b through 6.0) define
> the FADT.CENTURY field as:
> 
>   The RTC CMOS RAM index to the century of data value (hundred and
>   thousand year decimals). If this field contains a zero, then the RTC
>   centenary feature is not supported. If this field has a non-zero
> value, then this field contains an index into RTC RAM space that OSPM
> can use to program the centenary field.
> 
> The x86 targets generate ACPI payload, emulate an RTC
> (CONFIG_MC146818RTC), and that RTC supports the "centenary
> feature" (see occurrences of RTC_CENTURY in cmos_ioport_write() and
> cmos_ioport_read() in "hw/timer/mc146818rtc.c".)
> 
> However, FADT.CENTURY is left at zero currently:
> 
>   [06Ch 0108   1]            RTC Century Index : 00
> 
> which -- according to analysis done by Ruiyu Ni at Intel -- should
> cause Linux and Windows 8+ to think the RTC centenary feature is
> unavailable, and cause Windows 7 to (incorrectly) assume that the
> offset to use is constant 0x32. (0x32 happens to be the right value
> on QEMU, but Windows 7 is wrong to assume anything at all).
> 
> Exposing the right nonzero offset in FADT.CENTURY informs Linux and
> Windows 8+ about the right capabilities of the hardware, plus it
> retrofits our FADT to Windows 7's behavior.
> 
> Regression tested with the following guests (all UEFI installs):
> - i386 Q35: Fedora 21 ("Fedlet" edition)
> - x86_64:
>   - i440fx:
>     - Fedora 21
>     - RHEL 6 and 7
>     - Windows 7 and 10
>     - Windows Server 2008 R2 and 2012 R2
>   - Q35:
>     - Fedora 22
>     - Windows 8.1
> 
> Cc: "Michael S. Tsirkin" <address@hidden> (supporter:ACPI/SMBIOS)
> Cc: Igor Mammedov <address@hidden> (supporter:ACPI/SMBIOS)
> Cc: Paolo Bonzini <address@hidden> (maintainer:X86)
> Cc: Richard Henderson <address@hidden> (maintainer:X86)
> Cc: Eduardo Habkost <address@hidden> (maintainer:X86)
> Cc: Ruiyu Ni <address@hidden>
> Signed-off-by: Laszlo Ersek <address@hidden>
> ---
>  hw/i386/acpi-build.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> index 95e0c65..c5e6c4b 100644
> --- a/hw/i386/acpi-build.c
> +++ b/hw/i386/acpi-build.c
> @@ -42,6 +42,7 @@
>  #include "sysemu/tpm.h"
>  #include "hw/acpi/tpm.h"
>  #include "sysemu/tpm_backend.h"
> +#include "hw/timer/mc146818rtc_regs.h"
>  
>  /* Supported chipsets: */
>  #include "hw/acpi/piix4.h"
> @@ -334,6 +335,7 @@ static void fadt_setup(AcpiFadtDescriptorRev1
> *fadt, AcpiPmInfo *pm) if (max_cpus > 8) {
>          fadt->flags |= cpu_to_le32(1 <<
> ACPI_FADT_F_FORCE_APIC_CLUSTER_MODEL); }
> +    fadt->century = RTC_CENTURY;
>  }
>  
>  

Reviewed-by: Igor Mammedov <address@hidden>