[PATCH 4/4] HID: core: Export device version via HID_FIRMWARE_VERSION uevent

[Daniel Schaefer <dhs@frame.work>]

Expose the HID device version to userspace via the new
HID_FIRMWARE_VERSION uevent property. This enables userspace tools
(such as fwupd and hidapi) to retrieve device firmware version
information, providing parity with Windows HidD_GetAttributes() API
which returns VID, PID, and VersionNumber.

The version is exported as a 4-digit uppercase hexadecimal value
(e.g., "0100" for version 1.0), consistent with how USB devices
report bcdDevice.

fwupd can handle this since:
https://github.com/fwupd/fwupd/commit/fb0d4cc98abe253003ea0e1837277fd42971e0de
But the kernel hasn't yet exposed this.

hidapi patch is in-flight: https://github.com/libusb/hidapi/pull/777

Cc: Richard Hughes <richard@hughsie.com>
Cc: Mario Limonciello <mario.limonciello@amd.com>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Benjamin Tissoires <bentiss@kernel.org>
Cc: linux@frame.work
Signed-off-by: Daniel Schaefer <dhs@frame.work>
---
 drivers/hid/hid-core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
index da57cbf0af26..c2075d5b40c3 100644
--- a/drivers/hid/hid-core.c
+++ b/drivers/hid/hid-core.c
@@ -2884,6 +2884,9 @@ static int hid_uevent(const struct device *dev, struct kobj_uevent_env *env)
 	if (add_uevent_var(env, "HID_UNIQ=%s", hdev->uniq))
 		return -ENOMEM;
 
+	if (add_uevent_var(env, "HID_FIRMWARE_VERSION=%04X", hdev->version))
+		return -ENOMEM;
+
 	if (add_uevent_var(env, "MODALIAS=hid:b%04Xg%04Xv%08Xp%08X",
 			   hdev->bus, hdev->group, hdev->vendor, hdev->product))
 		return -ENOMEM;
-- 
2.52.0