Re: [PATCH v2 03/21] x86: q35: generate WDAT ACPI table

[Zhao Liu <zhao1.liu@intel.com>]

On Tue, Mar 03, 2026 at 10:25:14AM +0100, Igor Mammedov wrote:
> Date: Tue,  3 Mar 2026 10:25:14 +0100
> From: Igor Mammedov <imammedo@redhat.com>
> Subject: [PATCH v2 03/21] x86: q35: generate WDAT ACPI table
> 
> It will generate WDAT table [1] customized for TCO watchdog.
> This allows Windows guests (Windows Server 2008/Vista+) to
> use TCO watchdog using built-in generic driver, which
> alleviates need to install vendor specific drivers.
> 
> Given that enabling it might change guest behaviour
> (both Windows/Linux) the feature is disabled by default.
> 
> Users that need it can enable the feature with
> following CLI option.
>     -machine wdat=on
> 
> 1)
>    "Hardware Watchdog Timers Design Specification"
>     https://uefi.org/acpi 'Watchdog Action Table (WDAT)'
> 
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> Reviewed-by: Ani Sinha <anisinha@redhat.com>
> ---
>  include/hw/acpi/wdat-ich9.h | 15 +++++++
>  hw/acpi/meson.build         |  3 +-
>  hw/acpi/wdat-ich9-stub.c    | 15 +++++++
>  hw/acpi/wdat-ich9.c         | 90 +++++++++++++++++++++++++++++++++++++
>  hw/i386/acpi-build.c        | 12 +++++
>  5 files changed, 134 insertions(+), 1 deletion(-)
>  create mode 100644 include/hw/acpi/wdat-ich9.h
>  create mode 100644 hw/acpi/wdat-ich9-stub.c
>  create mode 100644 hw/acpi/wdat-ich9.c

...

> +void build_ich9_wdat(GArray *table_data, BIOSLinker *linker, const char *oem_id,
> +                     const char *oem_table_id, uint64_t tco_base)
> +{
> +    AcpiTable table = { .sig = "WDAT", .rev = 1, .oem_id = oem_id,
> +                        .oem_table_id = oem_table_id };
> +    struct AcpiGenericAddress tco_rld =  TCO_REG(tco_base, 0x0, 16);
> +    struct AcpiGenericAddress tco2_sts = TCO_REG(tco_base, 0x6, 16);
> +    struct AcpiGenericAddress tco1_cnt = TCO_REG(tco_base, 0x8, 16);
> +    struct AcpiGenericAddress tco_tmr =  TCO_REG(tco_base, 0x12, 16);
> +
> +    acpi_table_begin(&table, table_data);
> +    build_append_int_noprefix(table_data, 0x20, 4); /* Watchdog Header Length */
> +    build_append_int_noprefix(table_data, 0xff, 2); /* PCI Segment */
> +    build_append_int_noprefix(table_data, 0xff, 1); /* PCI Bus Number */
> +    build_append_int_noprefix(table_data, 0xff, 1); /* PCI Device Number */
> +    build_append_int_noprefix(table_data, 0xff, 1); /* PCI Function Number */
> +    build_append_int_noprefix(table_data, 0, 3);    /* Reserved */
> +    /*
> +     * limits/resolution are defined by ICH9 TCO spec
> +     */
> +    build_append_int_noprefix(table_data, 0x258, 4);/* Timer Period, ms */
> +    build_append_int_noprefix(table_data, 0x3ff, 4);/* Maximum Count */
> +    build_append_int_noprefix(table_data, 0x4, 4);  /* Minimum Count */

Spec said: The time-out period before the WDT fires is recommended to be at
least 5 minutes and is required to be less than 4,294,967,296 count
intervals.

Here we encode 0x4 * 0x258 = 2400ms, less than 5 minutes. But I
understand because "5 minutes" is just "recommanded" by spec, so 2400ms is
okay.

LGTM,

Reviewed-by: Zhao Liu <zhao1.liu@intel.com>