[PATCH v2 1/3] HID: asus: export asus_hid_fnlock_notify() for direct fn-lock control

["Marcus Grenängen" <marcus@grenangen.se>]

Some ASUS platforms cannot control fn-lock via WMI DEVS and must send a
HID feature report directly to the N-Key keyboard device instead.

Add a module-level fnlock_hdev pointer (protected by a mutex) that is set
at probe time for devices with QUIRK_HID_FN_LOCK and cleared at remove.
Export asus_hid_fnlock_notify(bool) so that asus-armoury can call into
hid-asus without a circular dependency.

Signed-off-by: Marcus Grenängen <marcus@grenangen.se>
---
 drivers/hid/hid-asus.c                     | 43 +++++++++++++++++++++-
 include/linux/platform_data/x86/asus-wmi.h |  5 +++
 2 files changed, 47 insertions(+), 1 deletion(-)

diff --git a/drivers/hid/hid-asus.c b/drivers/hid/hid-asus.c
index d34d74df3dc0..8a51dacf35eb 100644
--- a/drivers/hid/hid-asus.c
+++ b/drivers/hid/hid-asus.c
@@ -584,6 +584,38 @@ static void asus_sync_fn_lock(struct work_struct *work)
 	asus_kbd_set_fn_lock(drvdata->hdev, drvdata->fn_lock);
 }
 
+/*
+ * Module-level reference to the HID device that handles fn-lock via feature
+ * report. Set at probe and cleared at remove for QUIRK_HID_FN_LOCK devices.
+ * Protected by fnlock_hdev_lock.
+ */
+static DEFINE_MUTEX(fnlock_hdev_lock);
+static struct hid_device *fnlock_hdev;
+
+/**
+ * asus_hid_fnlock_notify() - Set fn-lock state directly via HID feature report.
+ * @enabled: true to lock fn (F1-F12 primary), false to unlock.
+ *
+ * Called by asus-armoury on platforms where the WMI DEVS path for fn-lock is
+ * non-functional (e.g. ASUS ProArt P16, N-Key keyboard product ID 0x19B6).
+ *
+ * Returns 0 on success, -ENODEV if no fn-lock capable HID device is present.
+ */
+int asus_hid_fnlock_notify(bool enabled)
+{
+	int ret = -ENODEV;
+
+	guard(mutex)(&fnlock_hdev_lock);
+	if (fnlock_hdev) {
+		ret = asus_kbd_set_fn_lock(fnlock_hdev, enabled);
+		/* hid_hw_raw_request returns byte count on success; normalise to 0 */
+		if (ret > 0)
+			ret = 0;
+	}
+	return ret;
+}
+EXPORT_SYMBOL_GPL(asus_hid_fnlock_notify);
+
 static void asus_schedule_work(struct asus_kbd_leds *led)
 {
 	unsigned long flags;
@@ -969,6 +1001,8 @@ static int asus_input_configured(struct hid_device *hdev, struct hid_input *hi)
 		drvdata->fn_lock = true;
 		INIT_WORK(&drvdata->fn_lock_sync_work, asus_sync_fn_lock);
 		asus_kbd_set_fn_lock(hdev, true);
+		guard(mutex)(&fnlock_hdev_lock);
+		fnlock_hdev = hdev;
 	}
 
 	if (drvdata->tp) {
@@ -1008,6 +1042,8 @@ static int asus_input_configured(struct hid_device *hdev, struct hid_input *hi)
 		drvdata->fn_lock = true;
 		INIT_WORK(&drvdata->fn_lock_sync_work, asus_sync_fn_lock);
 		asus_kbd_set_fn_lock(hdev, true);
+		guard(mutex)(&fnlock_hdev_lock);
+		fnlock_hdev = hdev;
 	}
 
 	return 0;
@@ -1362,8 +1398,13 @@ static void asus_remove(struct hid_device *hdev)
 		cancel_work_sync(&drvdata->kbd_backlight->work);
 	}
 
-	if (drvdata->quirks & QUIRK_HID_FN_LOCK)
+	if (drvdata->quirks & QUIRK_HID_FN_LOCK) {
+		scoped_guard(mutex, &fnlock_hdev_lock) {
+			if (fnlock_hdev == hdev)
+				fnlock_hdev = NULL;
+		}
 		cancel_work_sync(&drvdata->fn_lock_sync_work);
+	}
 
 	hid_hw_stop(hdev);
 }
diff --git a/include/linux/platform_data/x86/asus-wmi.h b/include/linux/platform_data/x86/asus-wmi.h
index 554f41b827e1..20facd5da74e 100644
--- a/include/linux/platform_data/x86/asus-wmi.h
+++ b/include/linux/platform_data/x86/asus-wmi.h
@@ -196,6 +196,7 @@ int asus_wmi_evaluate_method(u32 method_id, u32 arg0, u32 arg1, u32 *retval);
 int asus_hid_register_listener(struct asus_hid_listener *cdev);
 void asus_hid_unregister_listener(struct asus_hid_listener *cdev);
 int asus_hid_event(enum asus_hid_event event);
+int asus_hid_fnlock_notify(bool enabled);
 #else
 static inline void set_ally_mcu_hack(enum asus_ally_mcu_hack status)
 {
@@ -227,6 +228,10 @@ static inline int asus_hid_event(enum asus_hid_event event)
 {
 	return -ENODEV;
 }
+static inline int asus_hid_fnlock_notify(bool enabled)
+{
+	return -ENODEV;
+}
 #endif
 
 #endif	/* __PLATFORM_DATA_X86_ASUS_WMI_H */
-- 
2.54.0