[PATCH v3] platform/x86: add Xiaomi WMI key driver

[Lucy Wong <lucywong2778@gmail.com>]

Certain Xiaomi laptops expose extra function keys through a single WMI
event GUID (B74AF83F-8B2F-4069-ACAC-36D176F62FC0). Unlike the existing
xiaomi-wmi driver where each key has its own GUID, here all keys share
one GUID and the event buffer encodes both an event type and a keycode:

  buffer[1] = event type
    0x01: keyboard backlight level (EC handled)
    0x02: press/release keys (5 keys with abstract icons)
    0x03: firmware-handled toggles (touchpad, Fn lock)
  buffer[2] = keycode within that type

The keys with abstract icons are mapped to programmable macro keys for
userspace to bind. The backlight and toggle events are handled by the
firmware and are ignored.

Link: https://lore.kernel.org/platform-driver-x86/20260601151404.93049-1-lucywong2778@gmail.com/
Signed-off-by: Lucy Wong <lucywong2778@gmail.com>
---
Changes in v3:
- Add a mutex to serialize sparse_keymap_report_event() calls
- Document event types 0x01 and 0x03 with named defines
- Use dev_notice() for unknown key indices
- Fix reverse XMAS tree ordering of the notify() locals
- Set .probe_type = PROBE_PREFER_ASYNCHRONOUS

Changes in v2:
- Convert to .notify_new and set .min_event_size
- Ignore firmware-handled backlight and toggle events, which removes the
  toggle deduplication state
- Add the missing select INPUT_SPARSEKMAP
- Name the event codes and align the defines
- Add the dev_printk.h include

Re: BMOF data -- the WMI device does not expose embedded BMOF data; there
is no bmof sysfs attribute for B74AF83F-8B2F-4069-ACAC-36D176F62FC0.
---
 MAINTAINERS                            |   6 ++
 drivers/platform/x86/Kconfig           |  12 +++
 drivers/platform/x86/Makefile          |   1 +
 drivers/platform/x86/xiaomi-wmi-keys.c | 134 +++++++++++++++++++++++++
 4 files changed, 153 insertions(+)
 create mode 100644 drivers/platform/x86/xiaomi-wmi-keys.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 748ce4d1c6a2..0a280e6773a7 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -30546,6 +30546,12 @@ F:	fs/xfs/
 F:	include/uapi/linux/dqblk_xfs.h
 F:	include/uapi/linux/fsmap.h
 
+XIAOMI WMI KEYS DRIVER
+M:	Lucy Wong <lucywong2778@gmail.com>
+L:	platform-driver-x86@vger.kernel.org
+S:	Maintained
+F:	drivers/platform/x86/xiaomi-wmi-keys.c
+
 XILINX AMS DRIVER
 M:	Sai Krishna Potthuri <sai.krishna.potthuri@amd.com>
 M:	Conall O'Griofa <conall.ogriofa@amd.com>
diff --git a/drivers/platform/x86/Kconfig b/drivers/platform/x86/Kconfig
index 9ce384e0475e..efebf9e55b98 100644
--- a/drivers/platform/x86/Kconfig
+++ b/drivers/platform/x86/Kconfig
@@ -78,6 +78,18 @@ config XIAOMI_WMI
 	  To compile this driver as a module, choose M here: the module will
 	  be called xiaomi-wmi.
 
+config XIAOMI_WMI_KEYS
+	tristate "Xiaomi WMI key events driver"
+	depends on ACPI_WMI
+	depends on INPUT
+	select INPUT_SPARSEKMAP
+	help
+	  Say Y here if you want to support WMI-based hotkey events on certain
+	  Xiaomi laptops.
+
+	  To compile this driver as a module, choose M here: the module will
+	  be called xiaomi-wmi-keys.
+
 config REDMI_WMI
 	tristate "Redmibook WMI key driver"
 	depends on ACPI_WMI
diff --git a/drivers/platform/x86/Makefile b/drivers/platform/x86/Makefile
index 229057234d00..e77959052776 100644
--- a/drivers/platform/x86/Makefile
+++ b/drivers/platform/x86/Makefile
@@ -9,6 +9,7 @@ obj-$(CONFIG_HUAWEI_WMI)		+= huawei-wmi.o
 obj-$(CONFIG_MXM_WMI)			+= mxm-wmi.o
 obj-$(CONFIG_NVIDIA_WMI_EC_BACKLIGHT)	+= nvidia-wmi-ec-backlight.o
 obj-$(CONFIG_XIAOMI_WMI)		+= xiaomi-wmi.o
+obj-$(CONFIG_XIAOMI_WMI_KEYS)		+= xiaomi-wmi-keys.o
 obj-$(CONFIG_REDMI_WMI)			+= redmi-wmi.o
 obj-$(CONFIG_GIGABYTE_WMI)		+= gigabyte-wmi.o
 obj-$(CONFIG_BITLAND_MIFS_WMI)		+= bitland-mifs-wmi.o
diff --git a/drivers/platform/x86/xiaomi-wmi-keys.c b/drivers/platform/x86/xiaomi-wmi-keys.c
new file mode 100644
index 000000000000..7452c6eb8eca
--- /dev/null
+++ b/drivers/platform/x86/xiaomi-wmi-keys.c
@@ -0,0 +1,134 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Xiaomi laptop WMI hotkey driver
+ *
+ * Copyright (C) 2026 Lucy Wong <lucywong2778@gmail.com>
+ */
+
+#include <linux/device.h>
+#include <linux/dev_printk.h>
+#include <linux/input.h>
+#include <linux/input/sparse-keymap.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/wmi.h>
+
+#define XIAOMI_WMI_EVENT_GUID	"B74AF83F-8B2F-4069-ACAC-36D176F62FC0"
+
+#define XIAOMI_EVENT_TYPE_BACKLIGHT	0x01 /* keyboard backlight (EC handled) */
+#define XIAOMI_EVENT_TYPE_KEY		0x02 /* press/release keys */
+#define XIAOMI_EVENT_TYPE_TOGGLE	0x03 /* touchpad/Fn-lock toggles (EC handled) */
+
+#define XIAOMI_KEY_PRESS_FIRST	0x01
+#define XIAOMI_KEY_COUNT	5
+#define XIAOMI_KEY_RELEASE_FIRST	\
+	(XIAOMI_KEY_PRESS_FIRST + XIAOMI_KEY_COUNT)
+
+struct xiaomi_wmi_keys_event {
+	u8 reserved;
+	u8 type;
+	u8 code;
+};
+
+struct xiaomi_wmi_keys {
+	struct input_dev *input_dev;
+	struct mutex key_lock;	/* Serializes sparse_keymap_report_event() */
+};
+
+static const struct key_entry xiaomi_wmi_keys_keymap[] = {
+	/* programmable keys with abstract icons */
+	{ KE_KEY, 0x01, { KEY_MACRO1 } },
+	{ KE_KEY, 0x02, { KEY_MACRO2 } },
+	{ KE_KEY, 0x03, { KEY_MACRO3 } },
+	{ KE_KEY, 0x04, { KEY_MACRO4 } },
+	{ KE_KEY, 0x05, { KEY_MACRO5 } },
+	{ KE_END, 0 },
+};
+
+static int xiaomi_wmi_keys_probe(struct wmi_device *wdev, const void *context)
+{
+	struct xiaomi_wmi_keys *data;
+	int ret;
+
+	data = devm_kzalloc(&wdev->dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+	dev_set_drvdata(&wdev->dev, data);
+
+	ret = devm_mutex_init(&wdev->dev, &data->key_lock);
+	if (ret)
+		return ret;
+
+	data->input_dev = devm_input_allocate_device(&wdev->dev);
+	if (!data->input_dev)
+		return -ENOMEM;
+
+	data->input_dev->name = "Xiaomi WMI keys";
+	data->input_dev->phys = "wmi/input0";
+	data->input_dev->id.bustype = BUS_HOST;
+
+	ret = sparse_keymap_setup(data->input_dev, xiaomi_wmi_keys_keymap, NULL);
+	if (ret)
+		return ret;
+
+	return input_register_device(data->input_dev);
+}
+
+static void xiaomi_wmi_keys_notify(struct wmi_device *wdev,
+				   const struct wmi_buffer *buffer)
+{
+	struct xiaomi_wmi_keys *data = dev_get_drvdata(&wdev->dev);
+	const struct xiaomi_wmi_keys_event *event = buffer->data;
+	unsigned int code;
+	bool pressed;
+
+	/*
+	 * Only the press/release keys are reported. Event types 0x01
+	 * (backlight) and 0x03 (touchpad and Fn-lock toggles) are handled by
+	 * the firmware and need no action from the driver.
+	 */
+	if (event->type != XIAOMI_EVENT_TYPE_KEY) {
+		dev_dbg(&wdev->dev, "ignoring event type 0x%02x\n", event->type);
+		return;
+	}
+
+	if (event->code >= XIAOMI_KEY_PRESS_FIRST &&
+	    event->code < XIAOMI_KEY_PRESS_FIRST + XIAOMI_KEY_COUNT) {
+		code = event->code;
+		pressed = true;
+	} else if (event->code >= XIAOMI_KEY_RELEASE_FIRST &&
+		   event->code < XIAOMI_KEY_RELEASE_FIRST + XIAOMI_KEY_COUNT) {
+		code = event->code - XIAOMI_KEY_COUNT;
+		pressed = false;
+	} else {
+		dev_notice(&wdev->dev, "unknown key index 0x%02x\n", event->code);
+		return;
+	}
+
+	mutex_lock(&data->key_lock);
+	sparse_keymap_report_event(data->input_dev, code, pressed, false);
+	mutex_unlock(&data->key_lock);
+}
+
+static const struct wmi_device_id xiaomi_wmi_keys_id_table[] = {
+	{ .guid_string = XIAOMI_WMI_EVENT_GUID },
+	{ }
+};
+MODULE_DEVICE_TABLE(wmi, xiaomi_wmi_keys_id_table);
+
+static struct wmi_driver xiaomi_wmi_keys_driver = {
+	.driver = {
+		.name = "xiaomi-wmi-keys",
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
+	},
+	.id_table = xiaomi_wmi_keys_id_table,
+	.min_event_size = sizeof(struct xiaomi_wmi_keys_event),
+	.probe = xiaomi_wmi_keys_probe,
+	.notify_new = xiaomi_wmi_keys_notify,
+	.no_singleton = true,
+};
+module_wmi_driver(xiaomi_wmi_keys_driver);
+
+MODULE_AUTHOR("Lucy Wong <lucywong2778@gmail.com>");
+MODULE_DESCRIPTION("Xiaomi laptop WMI hotkey driver");
+MODULE_LICENSE("GPL");
-- 
2.56.0