HID: hid-asus: reset the backlight brightness level on resume

Some devices managed by this driver automatically set brightness to 0
before entering a suspended state and reset it back to a default
brightness level after the resume:
this has the effect of having the kernel report wrong brightness
status after a sleep, and on some devices (like the Asus RC71L) that
brightness is the intensity of LEDs directly facing the user.

Fix the above issue by setting back brightness to the level it had
before entering a sleep state.
Signed-off-by: Denis Benato <benato.denis96@gmail.com>
Signed-off-by: Luke D. Jones <luke@ljones.dev>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-asus.c

@@ -1000,6 +1000,24 @@ static int asus_start_multitouch(struct hid_device *hdev)
 	return 0;
 }
 
+static int __maybe_unused asus_resume(struct hid_device *hdev) {
+	struct asus_drvdata *drvdata = hid_get_drvdata(hdev);
+	int ret = 0;
+
+	if (drvdata->kbd_backlight) {
+		const u8 buf[] = { FEATURE_KBD_REPORT_ID, 0xba, 0xc5, 0xc4,
+				drvdata->kbd_backlight->cdev.brightness };
+		ret = asus_kbd_set_report(hdev, buf, sizeof(buf));
+		if (ret < 0) {
+			hid_err(hdev, "Asus failed to set keyboard backlight: %d\n", ret);
+			goto asus_resume_err;
+		}
+	}
+
+asus_resume_err:
+	return ret;
+}
+
 static int __maybe_unused asus_reset_resume(struct hid_device *hdev)
 {
 	struct asus_drvdata *drvdata = hid_get_drvdata(hdev);
@@ -1294,6 +1312,7 @@ static struct hid_driver asus_driver = {
 	.input_configured       = asus_input_configured,
 #ifdef CONFIG_PM
 	.reset_resume           = asus_reset_resume,
+	.resume					= asus_resume,
 #endif
 	.event			= asus_event,
 	.raw_event		= asus_raw_event