wifi: rtl8xxxu: Register the LED and make it blink

If the chip can have an LED, register a struct led_classdev and enable
hardware-controlled blinking. When the chip is not transmitting or
receiving anything the LED is off. Otherwise the LED will blink
faster or slower according to the throughput.

The LED can be controlled from userspace by writing 0, 1, or 2 to
/sys/class/leds/rtl8xxxu-usbX-Y/brightness:
0 - solid off.
1 - solid on.
2 - hardware-controlled blinking.

In this patch none of the chips advertise having an LED. That will be
added in the next patches.
Signed-off-by: Bitterblue Smith <rtl8821cerfe2@gmail.com>
Reviewed-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/b8235bca-60c3-d0fe-a958-53c6dd3ba3f6@gmail.com

drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu.h

@@ -1443,6 +1443,8 @@ struct rtl8xxxu_cfo_tracking {
 	u32 packet_count_pre;
 };
 
+#define RTL8XXXU_HW_LED_CONTROL	2
+
 struct rtl8xxxu_priv {
 	struct ieee80211_hw *hw;
 	struct usb_device *udev;
@@ -1564,6 +1566,10 @@ struct rtl8xxxu_priv {
 	struct rtl8xxxu_ra_report ra_report;
 	struct rtl8xxxu_cfo_tracking cfo_tracking;
 	struct rtl8xxxu_ra_info ra_info;
+
+	bool led_registered;
+	char led_name[32];
+	struct led_classdev led_cdev;
 };
 
 struct rtl8xxxu_rx_urb {
@@ -1613,6 +1619,8 @@ struct rtl8xxxu_fileops {
 			     u32 rts_rate);
 	void (*set_crystal_cap) (struct rtl8xxxu_priv *priv, u8 crystal_cap);
 	s8 (*cck_rssi) (struct rtl8xxxu_priv *priv, u8 cck_agc_rpt);
+	int (*led_classdev_brightness_set) (struct led_classdev *led_cdev,
+					    enum led_brightness brightness);
 	int writeN_block_size;
 	int rx_agg_buf_size;
 	char tx_desc_size;

drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_core.c

@@ -6955,6 +6955,40 @@ static int rtl8xxxu_parse_usb(struct rtl8xxxu_priv *priv,
 	return ret;
 }
 
+static void rtl8xxxu_init_led(struct rtl8xxxu_priv *priv)
+{
+	struct led_classdev *led = &priv->led_cdev;
+
+	if (!priv->fops->led_classdev_brightness_set)
+		return;
+
+	led->brightness_set_blocking = priv->fops->led_classdev_brightness_set;
+
+	snprintf(priv->led_name, sizeof(priv->led_name),
+		 "rtl8xxxu-usb%s", dev_name(&priv->udev->dev));
+	led->name = priv->led_name;
+	led->max_brightness = RTL8XXXU_HW_LED_CONTROL;
+
+	if (led_classdev_register(&priv->udev->dev, led))
+		return;
+
+	priv->led_registered = true;
+
+	led->brightness = led->max_brightness;
+	priv->fops->led_classdev_brightness_set(led, led->brightness);
+}
+
+static void rtl8xxxu_deinit_led(struct rtl8xxxu_priv *priv)
+{
+	struct led_classdev *led = &priv->led_cdev;
+
+	if (!priv->led_registered)
+		return;
+
+	priv->fops->led_classdev_brightness_set(led, LED_OFF);
+	led_classdev_unregister(led);
+}
+
 static int rtl8xxxu_probe(struct usb_interface *interface,
 			  const struct usb_device_id *id)
 {
@@ -7135,6 +7169,8 @@ static int rtl8xxxu_probe(struct usb_interface *interface,
 		goto err_set_intfdata;
 	}
 
+	rtl8xxxu_init_led(priv);
+
 	return 0;
 
 err_set_intfdata:
@@ -7159,6 +7195,8 @@ static void rtl8xxxu_disconnect(struct usb_interface *interface)
 	hw = usb_get_intfdata(interface);
 	priv = hw->priv;
 
+	rtl8xxxu_deinit_led(priv);
+
 	ieee80211_unregister_hw(hw);
 
 	priv->fops->power_off(priv);