thinkpad_acpi: return -NODEV while operating uninitialized LEDs

Not all 0-15 LEDs are available for all models, sometimes it's even not
safe. This patch return -NODEV while operating uninitialized LEDs.
Signed-off-by: Adam Lee <adam.lee@canonical.com>
Acked-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>

drivers/platform/x86/thinkpad_acpi.c

@@ -369,7 +369,7 @@ struct tpacpi_led_classdev {
 	struct led_classdev led_classdev;
 	struct work_struct work;
 	enum led_status_t new_state;
-	unsigned int led;
+	int led;
 };
 
 /* brightness level capabilities */
@@ -5313,6 +5313,8 @@ static int __init led_init(struct ibm_init_struct *iibm)
 					  ARRAY_SIZE(led_useful_qtable));
 
 	for (i = 0; i < TPACPI_LED_NUMLEDS; i++) {
+		tpacpi_leds[i].led = -1;
+
 		if (!tpacpi_is_led_restricted(i) &&
 		    test_bit(i, &useful_leds)) {
 			rc = tpacpi_init_led(i);
@@ -5370,9 +5372,13 @@ static int led_write(char *buf)
 		return -ENODEV;
 
 	while ((cmd = next_cmd(&buf))) {
-		if (sscanf(cmd, "%d", &led) != 1 || led < 0 || led > 15)
+		if (sscanf(cmd, "%d", &led) != 1)
 			return -EINVAL;
 
+		if (led < 0 || led > (TPACPI_LED_NUMLEDS - 1) ||
+				tpacpi_leds[led].led < 0)
+			return -ENODEV;
+
 		if (strstr(cmd, "off")) {
 			s = TPACPI_LED_OFF;
 		} else if (strstr(cmd, "on")) {