HID: Include firmware version in the uevent

Userspace software fwupd probes some HID devices when the daemon starts
up to determine the current firmware version in order to be able to offer
updated firmware if the manufacturer has made it available.

In order to do this fwupd will detach the existing kernel driver if one
is present, send a HID command and then reattach the kernel driver.

This can be problematic if the user is using the HID device at the time
that fwupd probes the hardware and can cause a few frames of input to be
dropped.  In some cases HID drivers already have a command to look up the
firmware version, and so if that is exported to userspace fwupd can
discover it and avoid needing to detach the kernel driver until it's time
to update the device.

Introduce a new member in the struct hid_device for the version and export
a new uevent variable HID_FIRMWARE_VERSION that will display the version
that HID drivers obtained.

Reviewed-by: Derek J. Clark <derekjohn.clark@gmail.com>
Reviewed-by: Mark Pearson <mpearson-lenovo@squebb.ca>
Cc: Richard Hughes <hughsient@gmail.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>

drivers/hid/hid-core.c

@@ -2887,6 +2887,11 @@ static int hid_uevent(const struct device *dev, struct kobj_uevent_env *env)
 	if (add_uevent_var(env, "MODALIAS=hid:b%04Xg%04Xv%08Xp%08X",
 			   hdev->bus, hdev->group, hdev->vendor, hdev->product))
 		return -ENOMEM;
+	if (hdev->firmware_version) {
+		if (add_uevent_var(env, "HID_FIRMWARE_VERSION=0x%04llX",
+				   hdev->firmware_version))
+			return -ENOMEM;
+	}
 
 	return 0;
 }

include/linux/hid.h

@@ -698,6 +698,7 @@ struct hid_device {
 	char name[128];							/* Device name */
 	char phys[64];							/* Device physical location */
 	char uniq[64];							/* Device unique identifier (serial #) */
+	u64 firmware_version;						/* Firmware version */
 
 	void *driver_data;