mfd: rtsx_usb: Fix runtime PM deadlock

commit b166010f upstream.

sd_set_power_mode() in derived module drivers/mmc/host/rtsx_usb_sdmmc.c
acquires dev_mutex and then calls pm_runtime_get_sync() to make sure the
device is awake while initializing a newly inserted card. Once it is
called during suspending state and explicitly before rtsx_usb_suspend()
acquires the same dev_mutex, both routine deadlock and further hang the
driver because pm_runtime_get_sync() waits the pending PM operations.

Fix this by using an empty suspend method. mmc_core always turns the
LED off after a request is done and thus it is ok to remove the only
rtsx_usb_turn_off_led() here.

Fixes: 730876be ("mfd: Add realtek USB card reader driver")
Signed-off-by: Roger Tseng <rogerable@realtek.com>
[Lee: Removed newly unused variable]
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

drivers/mfd/rtsx_usb.c

@@ -681,21 +681,10 @@ static void rtsx_usb_disconnect(struct usb_interface *intf)
 #ifdef CONFIG_PM
 static int rtsx_usb_suspend(struct usb_interface *intf, pm_message_t message)
 {
-	struct rtsx_ucr *ucr =
-		(struct rtsx_ucr *)usb_get_intfdata(intf);
 
 	dev_dbg(&intf->dev, "%s called with pm message 0x%04u\n",
 			__func__, message.event);
 
-	/*
-	 * Call to make sure LED is off during suspend to save more power.
-	 * It is NOT a permanent state and could be turned on anytime later.
-	 * Thus no need to call turn_on when resunming.
-	 */
-	mutex_lock(&ucr->dev_mutex);
-	rtsx_usb_turn_off_led(ucr);
-	mutex_unlock(&ucr->dev_mutex);
-
 	return 0;
 }