[PATCH v2 4/4] hw/acpi: Introduce the QEMU lid button

[Leonid Bloch <lb.workbox@gmail.com>]

The lid button device communicates laptop lid state to the guest via ACPI.
It supports two modes of operation:

1. QMP control mode (default): Lid state is controlled programmatically
   via QMP commands for consistent behavior across environments.

2. Host mirroring mode (optional): The device reflects the host's lid
   button state from procfs (/proc/acpi/button/lid/*/state). State
   changes trigger ACPI notifications to the guest.

Properties:
- 'use-qmp': Enable QMP control mode (default: true)
- 'enable-procfs': Enable host lid button mirroring (default: false)
- 'probe_interval': Probe interval in ms for procfs mode (default: 2000)
- 'procfs_path': Override default procfs path /proc/acpi/button

The device implements the ACPI_DEV_AML_IF interface to generate its
own AML code, placing the LID0 device directly under \_SB scope.

QMP commands:
- lid-button-set-state: Set lid open/closed state
- query-lid-button: Query current lid state

Signed-off-by: Leonid Bloch <lb.workbox@gmail.com>
---
 MAINTAINERS                          |   6 +
 docs/specs/button.rst                | 189 ++++++++++++
 docs/specs/index.rst                 |   1 +
 hw/acpi/Kconfig                      |   4 +
 hw/acpi/button.c                     | 438 +++++++++++++++++++++++++++
 hw/acpi/meson.build                  |   1 +
 hw/acpi/trace-events                 |   5 +
 hw/i386/Kconfig                      |   1 +
 include/hw/acpi/acpi_dev_interface.h |   1 +
 include/hw/acpi/button.h             |  25 ++
 qapi/acpi.json                       |  49 +++
 11 files changed, 720 insertions(+)
 create mode 100644 docs/specs/button.rst
 create mode 100644 hw/acpi/button.c
 create mode 100644 include/hw/acpi/button.h

diff --git a/MAINTAINERS b/MAINTAINERS
index 612efcb686..4d54a2ffb5 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2933,6 +2933,12 @@ S: Maintained
 F: hw/acpi/acad.*
 F: docs/specs/acad.rst
 
+Button
+M: Leonid Bloch <lb.workbox@gmail.com>
+S: Maintained
+F: hw/acpi/button.*
+F: docs/specs/button.rst
+
 Subsystems
 ----------
 Overall Audio backends
diff --git a/docs/specs/button.rst b/docs/specs/button.rst
new file mode 100644
index 0000000000..10a940b9f5
--- /dev/null
+++ b/docs/specs/button.rst
@@ -0,0 +1,189 @@
+.. SPDX-License-Identifier: GPL-2.0-or-later
+
+========================
+Laptop Lid Button Device
+========================
+
+The button device provides laptop lid button state information to the guest.
+It supports two operating modes:
+
+1. **QMP Control Mode** (default): Lid state is controlled via QMP commands,
+   providing deterministic control for testing and migration safety.
+2. **Procfs Mode**: Lid state mirrors the host's physical lid button, useful
+   for desktop virtualization where the guest should see the host's lid state.
+
+Configuration
+-------------
+
+The lid button device is created as an ISA device using ``-device button``.
+
+Operating Modes
+~~~~~~~~~~~~~~~
+
+**QMP Control Mode** (``use-qmp=true``, default)
+  Lid state is controlled via QMP commands. This mode is recommended for:
+
+  * Production environments requiring migration support
+  * Testing with predictable lid states
+  * Environments without host lid button access
+  * Security-sensitive deployments
+
+**Procfs Mode** (``enable-procfs=true``)
+  Lid mirrors the host's physical lid button. This mode is useful for:
+
+  * Desktop virtualization on laptops
+  * Development and testing with real lid button behavior
+
+  Note: Procfs mode reads host files and runs timers, which may impact
+  security and migration. Use with caution in production.
+
+Properties
+~~~~~~~~~~
+
+``ioport`` (default: 0x53d)
+  I/O port base address for the lid button device register.
+
+``use-qmp`` (default: true)
+  Enable QMP control mode. When true, lid state is controlled via
+  QMP commands. Cannot be used together with ``enable-procfs=true``.
+
+``enable-procfs`` (default: false)
+  Enable procfs mode to mirror the host's lid button. Cannot be used together
+  with ``use-qmp=true``.
+
+``probe_interval`` (default: 2000)
+  Time interval between periodic probes in milliseconds (procfs mode only).
+  The minimum allowed value is 10ms to prevent excessive polling.
+
+``procfs_path`` (default: /proc/acpi/button)
+  Path to the host's lid button procfs directory (procfs mode only). The device
+  will automatically scan this directory to find the lid state file. Use this
+  property to specify a different path or to provide a custom location for
+  testing purposes.
+
+Host Lid Button Detection
+-------------------------
+
+The host's lid button information is taken from::
+
+    /proc/acpi/button/lid/*/state
+
+This file is expected to be formatted as:
+
+- ``state:      open`` (if the lid is open)
+- ``state:      closed`` (if the lid is closed)
+
+These formats are based on the Linux 'button' driver.
+
+The device automatically scans the ``/proc/acpi/button/lid/`` directory
+for subdirectories containing a readable ``state`` file. If the procfs path
+differs, a different lid button needs to be probed, or even if a "fake" host
+lid button is to be provided, the ``procfs_path`` property allows overriding
+the default detection.
+
+ACPI Interface
+--------------
+
+The lid button device is exposed to the guest as an ACPI device with:
+
+- **HID**: ``PNP0C0D`` (Lid Device)
+- **Device Path**: ``\_SB.LID0``
+- **Notification Values**:
+
+  - ``0x80``: Status change (lid opened/closed)
+
+ACPI Methods
+~~~~~~~~~~~~
+
+``_LID`` (Lid Status)
+  Returns the current lid state (0 = closed, 1 = open).
+
+I/O Interface
+-------------
+
+The device uses a single I/O port register:
+
+- **Port**: ``ioport`` property value (default 0x53d)
+- **Size**: 1 byte
+- **Access**: Read-only
+
+Register Layout
+~~~~~~~~~~~~~~~
+
+**LIDS** (offset 0x00, 1 byte)
+  Current lid state:
+
+  - ``0x00``: Lid closed
+  - ``0x01``: Lid open
+
+QMP Commands
+------------
+
+When using QMP control mode (default), the following commands are available:
+
+``lid-button-set-state``
+  Set the lid button state.
+
+  * ``open``: Whether the lid is open (boolean)
+
+  Example::
+
+    -> { "execute": "lid-button-set-state",
+         "arguments": { "open": true }}
+    <- { "return": {} }
+
+``query-lid-button``
+  Query the current lid button state.
+
+  Example::
+
+    -> { "execute": "query-lid-button" }
+    <- { "return": { "open": true }}
+
+Examples
+--------
+
+QMP control mode (default - recommended)::
+
+  # Start with QMP control
+  qemu-system-x86_64 -device button -qmp tcp:localhost:4444,server,wait=off
+
+  # From another terminal, set lid state via QMP:
+  echo '{"execute":"qmp_capabilities"}
+        {"execute":"lid-button-set-state",
+         "arguments":{"open":false}}' | \
+  nc -N localhost 4444
+
+Procfs mode (mirror host lid button)::
+
+  # Enable procfs mode to mirror host lid button
+  qemu-system-x86_64 -device button,use-qmp=false,enable-procfs=true
+
+  # Custom probe interval (5 seconds)
+  qemu-system-x86_64 -device button,use-qmp=false,enable-procfs=true,probe_interval=5000
+
+  # Custom procfs path
+  qemu-system-x86_64 -device button,use-qmp=false,enable-procfs=true,procfs_path=/custom/path
+
+Testing with fake lid button::
+
+  # Create fake lid button files for testing
+  mkdir -p /tmp/fake_lid/lid/LID0
+  echo "state:      open" > /tmp/fake_lid/lid/LID0/state    # Format: "state:      open" or "state:      closed"
+
+  # Use fake lid button in procfs mode
+  qemu-system-x86_64 -device button,use-qmp=false,enable-procfs=true,procfs_path=/tmp/fake_lid
+
+  # Update lid state while VM is running (from another terminal)
+  echo "state:      closed" > /tmp/fake_lid/lid/LID0/state  # Close lid
+  echo "state:      open" > /tmp/fake_lid/lid/LID0/state    # Open lid
+
+Combined with other laptop devices::
+
+  # QMP mode (recommended)
+  qemu-system-x86_64 -device battery -device acad -device button
+
+  # Procfs/sysfs mode (desktop virtualization)
+  qemu-system-x86_64 -device battery,use-qmp=false,enable-sysfs=true \
+                     -device acad,use-qmp=false,enable-sysfs=true \
+                     -device button,use-qmp=false,enable-procfs=true
diff --git a/docs/specs/index.rst b/docs/specs/index.rst
index e144afcd90..e1c9b91b7b 100644
--- a/docs/specs/index.rst
+++ b/docs/specs/index.rst
@@ -24,6 +24,7 @@ guest hardware that is specific to QEMU.
    acpi_erst
    acad
    battery
+   button
    sev-guest-firmware
    fw_cfg
    fsi
diff --git a/hw/acpi/Kconfig b/hw/acpi/Kconfig
index 9d28c3addf..6600685855 100644
--- a/hw/acpi/Kconfig
+++ b/hw/acpi/Kconfig
@@ -73,6 +73,10 @@ config AC_ADAPTER
     bool
     depends on ACPI
 
+config BUTTON
+    bool
+    depends on ACPI
+
 config ACPI_HW_REDUCED
     bool
     select ACPI
diff --git a/hw/acpi/button.c b/hw/acpi/button.c
new file mode 100644
index 0000000000..dfe86af713
--- /dev/null
+++ b/hw/acpi/button.c
@@ -0,0 +1,438 @@
+/*
+ * QEMU emulated lid button device
+ *
+ * Copyright (c) 2019 Janus Technologies, Inc. (http://janustech.com)
+ *
+ * Authors:
+ *     Leonid Bloch <lb.workbox@gmail.com>
+ *     Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
+ *     Dmitry Fleytman <dmitry.fleytman@gmail.com>
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ *
+ */
+
+#include "qemu/osdep.h"
+#include "trace.h"
+#include "hw/isa/isa.h"
+#include "hw/acpi/acpi.h"
+#include "hw/nvram/fw_cfg.h"
+#include "qapi/error.h"
+#include "qemu/error-report.h"
+#include "hw/qdev-properties.h"
+#include "migration/vmstate.h"
+#include "hw/acpi/acpi_aml_interface.h"
+#include "qapi/qapi-commands-acpi.h"
+
+#include "hw/acpi/button.h"
+
+#define BUTTON_DEVICE(obj) OBJECT_CHECK(BUTTONState, (obj), \
+                                        TYPE_BUTTON)
+
+#define BUTTON_STA_ADDR            0
+
+#define PROCFS_PATH                "/proc/acpi/button"
+#define LID_DIR                    "lid"
+#define LID_STATE_FILE             "state"
+#define MIN_BUTTON_PROBE_INTERVAL  10  /* ms */
+#define MAX_ALLOWED_LINE_LENGTH    32  /* For convenience when comparing */
+
+enum {
+    LID_CLOSED = 0,
+    LID_OPEN = 1,
+};
+
+static const char *lid_state[] = { "closed", "open" };
+
+typedef struct BUTTONState {
+    ISADevice dev;
+    MemoryRegion io;
+    uint16_t ioport;
+    uint8_t lid_state;
+    bool use_qmp_control;
+    bool qmp_lid_open;
+    bool enable_procfs;
+
+    QEMUTimer *probe_state_timer;
+    uint64_t probe_state_interval;
+
+    char *button_path;
+    char lid_dir[MAX_ALLOWED_LINE_LENGTH];
+} BUTTONState;
+
+static inline bool button_file_accessible(char *path, const char *dir,
+                                          char *subdir, const char *file)
+{
+    char full_path[PATH_MAX];
+    int path_len;
+
+    path_len = snprintf(full_path, PATH_MAX, "%s/%s/%s/%s", path, dir, subdir,
+                        file);
+    if (path_len < 0 || path_len >= PATH_MAX) {
+        return false;
+    }
+
+    if (access(full_path, R_OK) == 0) {
+        return true;
+    }
+    return false;
+}
+
+static void button_get_lid_state(BUTTONState *s)
+{
+    char file_path[PATH_MAX];
+    int path_len;
+    char line[MAX_ALLOWED_LINE_LENGTH];
+    FILE *ff;
+
+    path_len = snprintf(file_path, PATH_MAX, "%s/%s/%s/%s", s->button_path,
+                        LID_DIR, s->lid_dir, LID_STATE_FILE);
+    if (path_len < 0 || path_len >= PATH_MAX) {
+        warn_report("Could not read the lid state.");
+        return;
+    }
+
+    ff = fopen(file_path, "r");
+    if (ff == NULL) {
+        warn_report("Could not read the lid state.");
+        return;
+    }
+
+    if (fgets(line, MAX_ALLOWED_LINE_LENGTH, ff) == NULL) {
+        warn_report("Lid state unreadable.");
+    } else {
+        if (strstr(line, lid_state[LID_OPEN]) != NULL) {
+            s->lid_state = LID_OPEN;
+        } else if (strstr(line, lid_state[LID_CLOSED]) != NULL) {
+            s->lid_state = LID_CLOSED;
+        } else {
+            warn_report("Lid state undetermined.");
+        }
+    }
+
+    fclose(ff);
+}
+
+static void button_get_dynamic_status(BUTTONState *s)
+{
+    trace_button_get_dynamic_status();
+
+    if (s->use_qmp_control) {
+        s->lid_state = s->qmp_lid_open ? LID_OPEN : LID_CLOSED;
+    } else if (s->enable_procfs) {
+        button_get_lid_state(s);
+    } else {
+        s->lid_state = LID_CLOSED;
+    }
+}
+
+static void button_probe_state(void *opaque)
+{
+    BUTTONState *s = opaque;
+
+    uint8_t lid_state_before = s->lid_state;
+
+    button_get_dynamic_status(s);
+
+    if (lid_state_before != s->lid_state) {
+        Object *obj = object_resolve_path_type("", TYPE_ACPI_DEVICE_IF, NULL);
+        acpi_send_event(DEVICE(obj), ACPI_BUTTON_CHANGE_STATUS);
+    }
+    timer_mod(s->probe_state_timer, qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL) +
+              s->probe_state_interval);
+}
+
+static void button_probe_state_timer_init(BUTTONState *s)
+{
+    if (s->enable_procfs && s->probe_state_interval > 0) {
+        s->probe_state_timer = timer_new_ms(QEMU_CLOCK_VIRTUAL,
+                                            button_probe_state, s);
+        timer_mod(s->probe_state_timer, qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL) +
+                  s->probe_state_interval);
+    }
+}
+
+static inline bool button_verify_lid_procfs(char *path, char *lid_subdir)
+{
+    return button_file_accessible(path, LID_DIR, lid_subdir, LID_STATE_FILE);
+}
+
+static bool button_get_lid_dir(BUTTONState *s, char *path)
+{
+    DIR *dir;
+    char lid_path[PATH_MAX];
+    int path_len;
+    struct dirent *ent;
+
+    path_len = snprintf(lid_path, PATH_MAX, "%s/%s", path, LID_DIR);
+    if (path_len < 0 || path_len >= PATH_MAX) {
+        return false;
+    }
+
+    dir = opendir(lid_path);
+    if (dir == NULL) {
+        return false;
+    }
+
+    ent = readdir(dir);
+    while (ent != NULL) {
+        if (ent->d_name[0] != '.') {
+            if (button_verify_lid_procfs(path, ent->d_name)) {
+                path_len = snprintf(s->lid_dir, strlen(ent->d_name) + 1, "%s",
+                                    ent->d_name);
+                if (path_len < 0 || path_len > strlen(ent->d_name)) {
+                    return false;
+                }
+                closedir(dir);
+                return true;
+            }
+        }
+        ent = readdir(dir);
+    }
+    closedir(dir);
+    return false;
+}
+
+static bool get_button_path(DeviceState *dev)
+{
+    BUTTONState *s = BUTTON_DEVICE(dev);
+    char procfs_path[PATH_MAX];
+    int path_len;
+
+    if (s->button_path) {
+        path_len = snprintf(procfs_path, strlen(s->button_path) + 1, "%s",
+                            s->button_path);
+        if (path_len < 0 || path_len > strlen(s->button_path)) {
+            return false;
+        }
+    } else {
+        path_len = snprintf(procfs_path, sizeof(PROCFS_PATH), "%s",
+                            PROCFS_PATH);
+        if (path_len < 0 || path_len >= sizeof(PROCFS_PATH)) {
+            return false;
+        }
+    }
+
+    if (button_get_lid_dir(s, procfs_path)) {
+        qdev_prop_set_string(dev, BUTTON_PATH_PROP, procfs_path);
+        return true;
+    }
+
+    return false;
+}
+
+static void button_realize(DeviceState *dev, Error **errp)
+{
+    ISADevice *d = ISA_DEVICE(dev);
+    BUTTONState *s = BUTTON_DEVICE(dev);
+    FWCfgState *fw_cfg = fw_cfg_find();
+    uint16_t *button_port;
+    char err_details[32] = {};
+
+    trace_button_realize();
+
+    if (s->use_qmp_control && s->enable_procfs) {
+        error_setg(errp, "Cannot enable both QMP control and procfs mode");
+        return;
+    }
+
+    /* Initialize lid to open by default when in QMP mode */
+    if (s->use_qmp_control) {
+        s->qmp_lid_open = true;
+    }
+
+    if (s->probe_state_interval < MIN_BUTTON_PROBE_INTERVAL) {
+        error_setg(errp, "'probe_state_interval' must be greater than %d ms",
+                   MIN_BUTTON_PROBE_INTERVAL);
+        return;
+    }
+
+    if (s->enable_procfs) {
+        if (!s->button_path) {
+            strcpy(err_details, " Try using 'procfs_path='");
+        }
+
+        if (!get_button_path(dev)) {
+            error_setg(errp, "Button procfs path not found or unreadable.%s",
+                       err_details);
+            return;
+        }
+    }
+
+    isa_register_ioport(d, &s->io, s->ioport);
+
+    button_probe_state_timer_init(s);
+
+    if (!fw_cfg) {
+        return;
+    }
+
+    button_port = g_malloc(sizeof(*button_port));
+    *button_port = cpu_to_le16(s->ioport);
+    fw_cfg_add_file(fw_cfg, "etc/button-port", button_port,
+                    sizeof(*button_port));
+}
+
+static const Property button_device_properties[] = {
+    DEFINE_PROP_UINT16(BUTTON_IOPORT_PROP, BUTTONState, ioport, 0x53d),
+    DEFINE_PROP_BOOL("use-qmp", BUTTONState, use_qmp_control, true),
+    DEFINE_PROP_BOOL("enable-procfs", BUTTONState, enable_procfs, false),
+    DEFINE_PROP_UINT64(BUTTON_PROBE_STATE_INTERVAL, BUTTONState,
+                       probe_state_interval, 2000),
+    DEFINE_PROP_STRING(BUTTON_PATH_PROP, BUTTONState, button_path),
+};
+
+static const VMStateDescription button_vmstate = {
+    .name = "button",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .fields = (VMStateField[]) {
+        VMSTATE_UINT16(ioport, BUTTONState),
+        VMSTATE_UINT64(probe_state_interval, BUTTONState),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
+static void build_button_aml(AcpiDevAmlIf *adev, Aml *scope)
+{
+    Aml *dev, *field, *method;
+    Aml *button_state;
+    Aml *sb_scope;
+    BUTTONState *s = BUTTON_DEVICE(adev);
+
+    button_state = aml_local(0);
+
+    sb_scope = aml_scope("\\_SB");
+    dev = aml_device("LID0");
+    aml_append(dev, aml_name_decl("_HID", aml_string("PNP0C0D")));
+
+    aml_append(dev, aml_operation_region("LSTA", AML_SYSTEM_IO,
+                                         aml_int(s->ioport),
+                                         BUTTON_LEN));
+    field = aml_field("LSTA", AML_BYTE_ACC, AML_NOLOCK, AML_PRESERVE);
+    aml_append(field, aml_named_field("LIDS", 8));
+    aml_append(dev, field);
+
+    method = aml_method("_LID", 0, AML_NOTSERIALIZED);
+    aml_append(method, aml_store(aml_name("LIDS"), button_state));
+    aml_append(method, aml_return(button_state));
+    aml_append(dev, method);
+
+    aml_append(sb_scope, dev);
+    aml_append(scope, sb_scope);
+
+    /* Status Change */
+    method = aml_method("\\_GPE._E0B", 0, AML_NOTSERIALIZED);
+    aml_append(method, aml_notify(aml_name("\\_SB.LID0"), aml_int(0x80)));
+    aml_append(scope, method);
+}
+
+static void button_class_init(ObjectClass *class, const void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(class);
+    AcpiDevAmlIfClass *adevc = ACPI_DEV_AML_IF_CLASS(class);
+
+    dc->realize = button_realize;
+    device_class_set_props(dc, button_device_properties);
+    dc->vmsd = &button_vmstate;
+    adevc->build_dev_aml = build_button_aml;
+}
+
+static uint64_t button_ioport_read(void *opaque, hwaddr addr, unsigned size)
+{
+    BUTTONState *s = opaque;
+
+    button_get_dynamic_status(s);
+
+    switch (addr) {
+    case BUTTON_STA_ADDR:
+        return s->lid_state;
+    default:
+        warn_report("Button: guest read unknown value.");
+        trace_button_ioport_read_unknown();
+        return 0;
+    }
+}
+
+static const MemoryRegionOps button_ops = {
+    .read = button_ioport_read,
+    .impl = {
+        .min_access_size = 1,
+        .max_access_size = 1,
+    },
+};
+
+static void button_instance_init(Object *obj)
+{
+    BUTTONState *s = BUTTON_DEVICE(obj);
+
+    memory_region_init_io(&s->io, obj, &button_ops, s, "button",
+                          BUTTON_LEN);
+}
+
+static const TypeInfo button_info = {
+    .name          = TYPE_BUTTON,
+    .parent        = TYPE_ISA_DEVICE,
+    .instance_size = sizeof(BUTTONState),
+    .class_init    = button_class_init,
+    .instance_init = button_instance_init,
+    .interfaces = (InterfaceInfo[]) {
+        { TYPE_ACPI_DEV_AML_IF },
+        { },
+    },
+};
+
+static BUTTONState *find_button_device(void)
+{
+    Object *o = object_resolve_path_type("", TYPE_BUTTON, NULL);
+    if (!o) {
+        return NULL;
+    }
+    return BUTTON_DEVICE(o);
+}
+
+void qmp_lid_button_set_state(bool open, Error **errp)
+{
+    BUTTONState *s = find_button_device();
+
+    if (!s) {
+        error_setg(errp, "No lid button device found");
+        return;
+    }
+
+    s->qmp_lid_open = open;
+
+    Object *obj = object_resolve_path_type("", TYPE_ACPI_DEVICE_IF, NULL);
+    if (obj) {
+        acpi_send_event(DEVICE(obj), ACPI_BUTTON_CHANGE_STATUS);
+    }
+}
+
+LidButtonInfo *qmp_query_lid_button(Error **errp)
+{
+    BUTTONState *s = find_button_device();
+    LidButtonInfo *ret;
+
+    if (!s) {
+        error_setg(errp, "No lid button device found");
+        return NULL;
+    }
+
+    ret = g_new0(LidButtonInfo, 1);
+
+    if (s->use_qmp_control) {
+        ret->open = s->qmp_lid_open;
+    } else {
+        button_get_dynamic_status(s);
+        ret->open = (s->lid_state == LID_OPEN);
+    }
+
+    return ret;
+}
+
+static void button_register_types(void)
+{
+    type_register_static(&button_info);
+}
+
+type_init(button_register_types)
diff --git a/hw/acpi/meson.build b/hw/acpi/meson.build
index 2b24951f28..94993ecb9a 100644
--- a/hw/acpi/meson.build
+++ b/hw/acpi/meson.build
@@ -33,6 +33,7 @@ if have_tpm
 endif
 acpi_ss.add(when: 'CONFIG_BATTERY', if_true: files('battery.c'))
 acpi_ss.add(when: 'CONFIG_AC_ADAPTER', if_true: files('acad.c'))
+acpi_ss.add(when: 'CONFIG_BUTTON', if_true: files('button.c'))
 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_all(when: 'CONFIG_ACPI', if_true: acpi_ss)
diff --git a/hw/acpi/trace-events b/hw/acpi/trace-events
index 68ac6e9701..816f027bb3 100644
--- a/hw/acpi/trace-events
+++ b/hw/acpi/trace-events
@@ -97,3 +97,8 @@ battery_ioport_read_unknown(void) "Battery read unknown"
 acad_realize(void) "AC adapter device realize entry"
 acad_get_dynamic_status(uint8_t state) "AC adapter read state: %"PRIu8
 acad_ioport_read_unknown(void) "AC adapter read unknown"
+
+# button.c
+button_realize(void) "Button device realize entry"
+button_get_dynamic_status(void) "Button read dynamic status entry"
+button_ioport_read_unknown(void) "Button read unknown"
diff --git a/hw/i386/Kconfig b/hw/i386/Kconfig
index baab382a2e..1d2d809028 100644
--- a/hw/i386/Kconfig
+++ b/hw/i386/Kconfig
@@ -41,6 +41,7 @@ config PC
     imply FDC_ISA
     imply BATTERY
     imply AC_ADAPTER
+    imply BUTTON
     select I8259
     select I8254
     select PCKBD
diff --git a/include/hw/acpi/acpi_dev_interface.h b/include/hw/acpi/acpi_dev_interface.h
index 588fbbd05f..4f5bcc15da 100644
--- a/include/hw/acpi/acpi_dev_interface.h
+++ b/include/hw/acpi/acpi_dev_interface.h
@@ -15,6 +15,7 @@ typedef enum {
     ACPI_POWER_DOWN_STATUS = 64,
     ACPI_BATTERY_CHANGE_STATUS = 128,
     ACPI_AC_ADAPTER_CHANGE_STATUS = 1024,
+    ACPI_BUTTON_CHANGE_STATUS = 2048,
 } AcpiEventStatusBits;
 
 #define TYPE_ACPI_DEVICE_IF "acpi-device-interface"
diff --git a/include/hw/acpi/button.h b/include/hw/acpi/button.h
new file mode 100644
index 0000000000..fa5f7001b2
--- /dev/null
+++ b/include/hw/acpi/button.h
@@ -0,0 +1,25 @@
+/*
+ * QEMU emulated button device.
+ *
+ * Copyright (c) 2019 Janus Technologies, Inc. (http://janustech.com)
+ *
+ * Authors:
+ *     Leonid Bloch <lb.workbox@gmail.com>
+ *     Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
+ *     Dmitry Fleytman <dmitry.fleytman@gmail.com>
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ *
+ */
+
+#ifndef HW_ACPI_BUTTON_H
+#define HW_ACPI_BUTTON_H
+
+#define TYPE_BUTTON                  "button"
+#define BUTTON_IOPORT_PROP           "ioport"
+#define BUTTON_PATH_PROP             "procfs_path"
+#define BUTTON_PROBE_STATE_INTERVAL  "probe_interval"
+
+#define BUTTON_LEN                   1
+
+#endif
diff --git a/qapi/acpi.json b/qapi/acpi.json
index 52e151f0e6..bcbddbfbd5 100644
--- a/qapi/acpi.json
+++ b/qapi/acpi.json
@@ -264,3 +264,52 @@
 ##
 { 'command': 'query-ac-adapter',
   'returns': 'AcAdapterInfo' }
+
+##
+# @lid-button-set-state:
+#
+# Set the state of the emulated laptop lid button device
+#
+# @open: whether the lid is open
+#
+
+#
+# Since: 10.2
+#
+# .. qmp-example::
+#
+#     -> { "execute": "lid-button-set-state",
+#          "arguments": { "open": true } }
+#     <- { "return": {} }
+##
+{ 'command': 'lid-button-set-state',
+  'data': { 'open': 'bool' } }
+
+##
+# @LidButtonInfo:
+#
+# Lid button state information
+#
+# @open: whether the lid is open
+#
+# Since: 10.2
+##
+{ 'struct': 'LidButtonInfo',
+  'data': { 'open': 'bool' } }
+
+##
+# @query-lid-button:
+#
+# Query the current state of the emulated laptop lid button device
+#
+# Returns: lid button state
+#
+# Since: 10.2
+#
+# .. qmp-example::
+#
+#     -> { "execute": "query-lid-button" }
+#     <- { "return": { "open": true } }
+##
+{ 'command': 'query-lid-button',
+  'returns': 'LidButtonInfo' }
-- 
2.50.1