wifi: mt76: mt7921u: fix race issue between reset and suspend/resume

It is unexpected that the reset work is running simultaneously with
the suspend or resume context and it is possible that reset work is still
running even after mt7921 is suspended if we don't fix the race issue.

Thus, the suspend procedure should be waiting until the reset is completed
at the beginning and ignore the subsequent the reset requests.

In case there is an error that happens during either suspend or resume
handler, we will schedule a reset task to recover the error before
returning the error code to ensure we can immediately fix the error there.

Fixes: df3e4143ba8a ("mt76: mt7921u: add suspend/resume support")
Co-developed-by: YN Chen <YN.Chen@mediatek.com>
Signed-off-by: YN Chen <YN.Chen@mediatek.com>
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

mt7921/usb.c

@@ -301,23 +301,36 @@ static void mt7921u_disconnect(struct usb_interface *usb_intf)
 static int mt7921u_suspend(struct usb_interface *intf, pm_message_t state)
 {
 	struct mt7921_dev *dev = usb_get_intfdata(intf);
+	struct mt76_connac_pm *pm = &dev->pm;
 	int err;
 
+	pm->suspended = true;
+	flush_work(&dev->reset_work);
+
 	err = mt76_connac_mcu_set_hif_suspend(&dev->mt76, true);
 	if (err)
-		return err;
+		goto failed;
 
 	mt76u_stop_rx(&dev->mt76);
 	mt76u_stop_tx(&dev->mt76);
 
 	set_bit(MT76_STATE_SUSPEND, &dev->mphy.state);
 
 	return 0;
+
+failed:
+	pm->suspended = false;
+
+	if (err < 0)
+		mt7921_reset(&dev->mt76);
+
+	return err;
 }
 
 static int mt7921u_resume(struct usb_interface *intf)
 {
 	struct mt7921_dev *dev = usb_get_intfdata(intf);
+	struct mt76_connac_pm *pm = &dev->pm;
 	bool reinit = true;
 	int err, i;
 
@@ -339,16 +352,23 @@ static int mt7921u_resume(struct usb_interface *intf)
 	if (reinit || mt7921_dma_need_reinit(dev)) {
 		err = mt7921u_dma_init(dev, true);
 		if (err)
-			return err;
+			goto failed;
 	}
 
 	clear_bit(MT76_STATE_SUSPEND, &dev->mphy.state);
 
 	err = mt76u_resume_rx(&dev->mt76);
 	if (err < 0)
-		return err;
+		goto failed;
+
+	err = mt76_connac_mcu_set_hif_suspend(&dev->mt76, false);
+failed:
+	pm->suspended = false;
+
+	if (err < 0)
+		mt7921_reset(&dev->mt76);
 
-	return mt76_connac_mcu_set_hif_suspend(&dev->mt76, false);
+	return err;
 }
 #endif /* CONFIG_PM */