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Re: [Qemu-devel] [PATCH] hw/i386: fill in the CENTURY field of the FADT
From: |
Igor Mammedov |
Subject: |
Re: [Qemu-devel] [PATCH] hw/i386: fill in the CENTURY field of the FADT (FACP) ACPI table |
Date: |
Thu, 10 Dec 2015 19:53:36 +0100 |
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>