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

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, May 13, 2026 at 11:47:19PM +0800, Zhao Liu wrote:
> 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>


maybe a comment why it's shorter?