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
aleviates 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.
    -global 'ICH9-LPC.wdat=on'

1)
   "Hardware Watchdog Timers Design Specification"
    https://uefi.org/acpi 'Watchdog Action Table (WDAT)'

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
---
 include/hw/acpi/wdat.h |  3 ++
 hw/acpi/meson.build    |  3 +-
 hw/acpi/wdat-ich9.c    | 85 ++++++++++++++++++++++++++++++++++++++++++
 hw/acpi/wdat-stub.c    | 16 ++++++++
 hw/i386/acpi-build.c   | 13 +++++++
 5 files changed, 119 insertions(+), 1 deletion(-)
 create mode 100644 hw/acpi/wdat-ich9.c
 create mode 100644 hw/acpi/wdat-stub.c

diff --git a/include/hw/acpi/wdat.h b/include/hw/acpi/wdat.h
index c539e97e9b..67b9136d8c 100644
--- a/include/hw/acpi/wdat.h
+++ b/include/hw/acpi/wdat.h
@@ -115,4 +115,7 @@ void build_append_wdat_ins(GArray *table_data,
                            struct AcpiGenericAddress as,
                            uint32_t val, uint32_t mask);
 
+void build_wdat(GArray *table_data, BIOSLinker *linker, const char *oem_id,
+                const char *oem_table_id, uint64_t tco_base);
+
 #endif /* QEMU_HW_ACPI_WDAT_H */
diff --git a/hw/acpi/meson.build b/hw/acpi/meson.build
index 56b5d1ec96..fb4304f21c 100644
--- a/hw/acpi/meson.build
+++ b/hw/acpi/meson.build
@@ -24,7 +24,7 @@ acpi_ss.add(when: 'CONFIG_ACPI_PCI_BRIDGE', if_true: files('pci-bridge.c'))
 acpi_ss.add(when: 'CONFIG_ACPI_PCIHP', if_true: files('pcihp.c'))
 acpi_ss.add(when: 'CONFIG_ACPI_PCIHP', if_false: files('acpi-pci-hotplug-stub.c'))
 acpi_ss.add(when: 'CONFIG_ACPI_VIOT', if_true: files('viot.c'))
-acpi_ss.add(when: 'CONFIG_ACPI_ICH9', if_true: files('ich9.c', 'ich9_tco.c', 'ich9_timer.c'))
+acpi_ss.add(when: 'CONFIG_ACPI_ICH9', if_true: files('ich9.c', 'ich9_tco.c', 'ich9_timer.c', 'wdat-ich9.c'))
 acpi_ss.add(when: 'CONFIG_ACPI_ERST', if_true: files('erst.c'))
 acpi_ss.add(when: 'CONFIG_IPMI', if_true: files('ipmi.c'), if_false: files('ipmi-stub.c'))
 acpi_ss.add(when: 'CONFIG_PC', if_false: files('acpi-x86-stub.c'))
@@ -33,6 +33,7 @@ if have_tpm
 endif
 system_ss.add(when: 'CONFIG_ACPI', if_false: files('acpi-stub.c', 'aml-build-stub.c', 'ghes-stub.c', 'acpi_interface.c'))
 system_ss.add(when: 'CONFIG_ACPI_PCI_BRIDGE', if_false: files('pci-bridge-stub.c'))
+system_ss.add(when: 'CONFIG_ACPI_ICH9', if_false: files('wdat-stub.c'))
 system_ss.add_all(when: 'CONFIG_ACPI', if_true: acpi_ss)
 system_ss.add(when: 'CONFIG_GHES_CPER', if_true: files('ghes_cper.c'))
 system_ss.add(when: 'CONFIG_GHES_CPER', if_false: files('ghes_cper_stub.c'))
diff --git a/hw/acpi/wdat-ich9.c b/hw/acpi/wdat-ich9.c
new file mode 100644
index 0000000000..c32ecf922c
--- /dev/null
+++ b/hw/acpi/wdat-ich9.c
@@ -0,0 +1,85 @@
+/*
+ * TCO Watchdog Action Table (WDAT)
+ *
+ * Copyright Red Hat, Inc. 2025
+ * Author(s): Igor Mammedov <imammedo@redhat.com>
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "qemu/osdep.h"
+#include "hw/acpi/aml-build.h"
+#include "hw/acpi/wdat.h"
+#include "hw/southbridge/ich9.h"
+
+#define TCO_REG(base, reg_offset, reg_width) { .space_id = AML_AS_SYSTEM_IO, \
+            .address = base + reg_offset, .bit_width = reg_width, \
+            .access_width = AML_WORD_ACC, };
+
+/*
+ *   "Hardware Watchdog Timers Design Specification"
+ *       https://uefi.org/acpi 'Watchdog Action Table (WDAT)'
+ */
+void build_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 */
+    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 */
+    /*
+     * WATCHDOG_ENABLED & WATCHDOG_STOPPED_IN_SLEEP_STATE
+     */
+    build_append_int_noprefix(table_data, 0x81, 1); /* Watchdog Flags */
+    build_append_int_noprefix(table_data, 0, 3);    /* Reserved */
+    /*
+     * watchdog instruction entries
+     */
+    build_append_int_noprefix(table_data, 10, 4);
+    /* Action table */
+    build_append_wdat_ins(table_data, WDAT_ACTION_RESET,
+        WDAT_INS_WRITE_VALUE,
+        tco_rld, 0x1, 0x1ff);
+    build_append_wdat_ins(table_data, WDAT_ACTION_QUERY_RUNNING_STATE,
+        WDAT_INS_READ_VALUE,
+        tco1_cnt, 0x0, 0x800);
+    build_append_wdat_ins(table_data, WDAT_ACTION_SET_RUNNING_STATE,
+        WDAT_INS_WRITE_VALUE | WDAT_INS_PRESERVE_REGISTER,
+        tco1_cnt, 0, 0x800);
+    build_append_wdat_ins(table_data, WDAT_ACTION_QUERY_STOPPED_STATE,
+        WDAT_INS_READ_VALUE,
+        tco1_cnt, 0x800, 0x800);
+    build_append_wdat_ins(table_data, WDAT_ACTION_SET_STOPPED_STATE,
+        WDAT_INS_WRITE_VALUE | WDAT_INS_PRESERVE_REGISTER,
+        tco1_cnt, 0x800, 0x800);
+    build_append_wdat_ins(table_data, WDAT_ACTION_SET_COUNTDOWN_PERIOD,
+        WDAT_INS_WRITE_COUNTDOWN,
+        tco_tmr, 0x0, 0x3FF);
+    build_append_wdat_ins(table_data, WDAT_ACTION_QUERY_COUNTDOWN_PERIOD,
+        WDAT_INS_READ_COUNTDOWN,
+        tco_tmr, 0x0, 0x3FF);
+    build_append_wdat_ins(table_data, WDAT_ACTION_QUERY_WATCHDOG_STATUS,
+        WDAT_INS_READ_VALUE,
+        tco2_sts, 0x2, 0x2);
+    build_append_wdat_ins(table_data, WDAT_ACTION_SET_WATCHDOG_STATUS,
+        WDAT_INS_WRITE_VALUE | WDAT_INS_PRESERVE_REGISTER,
+        tco2_sts, 0x2, 0x2);
+    build_append_wdat_ins(table_data, WDAT_ACTION_SET_WATCHDOG_STATUS,
+        WDAT_INS_WRITE_VALUE | WDAT_INS_PRESERVE_REGISTER,
+        tco2_sts, 0x4, 0x4);
+
+    acpi_table_end(linker, &table);
+}
diff --git a/hw/acpi/wdat-stub.c b/hw/acpi/wdat-stub.c
new file mode 100644
index 0000000000..a9b57a047b
--- /dev/null
+++ b/hw/acpi/wdat-stub.c
@@ -0,0 +1,16 @@
+/*
+ * Copyright Red Hat, Inc. 2025
+ * Author(s): Igor Mammedov <imammedo@redhat.com>
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "qemu/osdep.h"
+#include "hw/acpi/aml-build.h"
+#include "hw/acpi/wdat.h"
+
+void build_wdat(GArray *table_data, BIOSLinker *linker, const char *oem_id,
+                const char *oem_table_id, uint64_t tco_base)
+{
+    g_assert_not_reached();
+}
diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
index 9446a9f862..ac420eab81 100644
--- a/hw/i386/acpi-build.c
+++ b/hw/i386/acpi-build.c
@@ -77,6 +77,7 @@
 
 #include "hw/acpi/hmat.h"
 #include "hw/acpi/viot.h"
+#include "hw/acpi/wdat.h"
 
 #include CONFIG_DEVICES
 
@@ -104,11 +105,13 @@ typedef struct AcpiPmInfo {
     bool smi_on_cpuhp;
     bool smi_on_cpu_unplug;
     bool pcihp_root_en;
+    bool wdat_enabled;
     uint8_t s4_val;
     AcpiFadtData fadt;
     uint16_t cpu_hp_io_base;
     uint16_t pcihp_io_base;
     uint16_t pcihp_io_len;
+    uint64_t tco_io_base;
 } AcpiPmInfo;
 
 typedef struct AcpiMiscInfo {
@@ -203,6 +206,7 @@ static void acpi_get_pm_info(MachineState *machine, AcpiPmInfo *pm)
     pm->pcihp_io_len = 0;
     pm->smi_on_cpuhp = false;
     pm->smi_on_cpu_unplug = false;
+    pm->wdat_enabled = false;
 
     assert(obj);
     init_common_fadt_data(machine, obj, &pm->fadt);
@@ -224,6 +228,9 @@ static void acpi_get_pm_info(MachineState *machine, AcpiPmInfo *pm)
             !!(smi_features & BIT_ULL(ICH9_LPC_SMI_F_CPU_HOTPLUG_BIT));
         pm->smi_on_cpu_unplug =
             !!(smi_features & BIT_ULL(ICH9_LPC_SMI_F_CPU_HOT_UNPLUG_BIT));
+        pm->wdat_enabled = object_property_get_bool(obj, "wdat", NULL);
+        pm->tco_io_base = object_property_get_uint(obj, ACPI_PM_PROP_PM_IO_BASE,
+            NULL) + ICH9_PMIO_TCO_RLD;
     }
     pm->pcihp_io_base =
         object_property_get_uint(obj, ACPI_PCIHP_IO_BASE_PROP, NULL);
@@ -2079,6 +2086,12 @@ void acpi_build(AcpiBuildTables *tables, MachineState *machine)
     acpi_add_table(table_offsets, tables_blob);
     build_waet(tables_blob, tables->linker, x86ms->oem_id, x86ms->oem_table_id);
 
+    if (pm.wdat_enabled == true) {
+        acpi_add_table(table_offsets, tables_blob);
+        build_wdat(tables_blob, tables->linker, x86ms->oem_id,
+                   x86ms->oem_table_id, pm.tco_io_base);
+    }
+
     /* Add tables supplied by user (if any) */
     for (u = acpi_table_first(); u; u = acpi_table_next(u)) {
         unsigned len = acpi_table_len(u);
-- 
2.47.3