rt2800usb: read TX_STA_FIFO asynchronously

Trying to fix the "TX status report missed" warnings
by reading the TX_STA_FIFO entries as quickly as possible.
The TX_STA_FIFO is too small in hardware, thus reading
it only from the workqueue is too slow and entries get lost.

Start an asynchronous read of the TX_STA_FIFO directly from
the TX URB completion callback (atomic context, thus it cannot
use the blocking rt2800_register_read()). If the async
read returns a valid FIFO entry, it is pushed into a larger
FIFO inside struct rt2x00_dev, until rt2800_txdone() picks
it up.

A .tx_dma_done callback is added to struct rt2x00lib_ops
to trigger the async read from the URB completion callback.
Signed-off-by: Johannes Stezenbach <js@sig21.net>
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rt2x00/rt2800lib.c

@@ -730,34 +730,20 @@ void rt2800_txdone(struct rt2x00_dev *rt2x00dev)
 	struct data_queue *queue;
 	struct queue_entry *entry;
 	u32 reg;
-	u8 pid;
-	int i;
+	u8 qid;
 
-	/*
-	 * TX_STA_FIFO is a stack of X entries, hence read TX_STA_FIFO
-	 * at most X times and also stop processing once the TX_STA_FIFO_VALID
-	 * flag is not set anymore.
-	 *
-	 * The legacy drivers use X=TX_RING_SIZE but state in a comment
-	 * that the TX_STA_FIFO stack has a size of 16. We stick to our
-	 * tx ring size for now.
-	 */
-	for (i = 0; i < rt2x00dev->ops->tx->entry_num; i++) {
-		rt2800_register_read(rt2x00dev, TX_STA_FIFO, &reg);
-		if (!rt2x00_get_field32(reg, TX_STA_FIFO_VALID))
-			break;
+	while (kfifo_get(&rt2x00dev->txstatus_fifo, &reg)) {
 
-		/*
-		 * Skip this entry when it contains an invalid
-		 * queue identication number.
+		/* TX_STA_FIFO_PID_QUEUE is a 2-bit field, thus
+		 * qid is guaranteed to be one of the TX QIDs
 		 */
-		pid = rt2x00_get_field32(reg, TX_STA_FIFO_PID_QUEUE);
-		if (pid >= QID_RX)
-			continue;
-
-		queue = rt2x00queue_get_tx_queue(rt2x00dev, pid);
-		if (unlikely(!queue))
+		qid = rt2x00_get_field32(reg, TX_STA_FIFO_PID_QUEUE);
+		queue = rt2x00queue_get_tx_queue(rt2x00dev, qid);
+		if (unlikely(!queue)) {
+			WARNING(rt2x00dev, "Got TX status for an unavailable "
+					   "queue %u, dropping\n", qid);
 			continue;
+		}
 
 		/*
 		 * Inside each queue, we process each entry in a chronological

drivers/net/wireless/rt2x00/rt2800usb.c

@@ -98,6 +98,35 @@ static void rt2800usb_stop_queue(struct data_queue *queue)
 	}
 }
 
+static void rt2800usb_tx_sta_fifo_read_completed(struct rt2x00_dev *rt2x00dev,
+						 int urb_status, u32 tx_status)
+{
+	if (urb_status) {
+		WARNING(rt2x00dev, "rt2x00usb_register_read_async failed: %d\n", urb_status);
+		return;
+	}
+
+	/* try to read all TX_STA_FIFO entries before scheduling txdone_work */
+	if (rt2x00_get_field32(tx_status, TX_STA_FIFO_VALID)) {
+		if (!kfifo_put(&rt2x00dev->txstatus_fifo, &tx_status)) {
+			WARNING(rt2x00dev, "TX status FIFO overrun, "
+				"drop tx status report.\n");
+			queue_work(rt2x00dev->workqueue, &rt2x00dev->txdone_work);
+		} else
+			rt2x00usb_register_read_async(rt2x00dev, TX_STA_FIFO,
+						      rt2800usb_tx_sta_fifo_read_completed);
+	} else if (!kfifo_is_empty(&rt2x00dev->txstatus_fifo))
+		queue_work(rt2x00dev->workqueue, &rt2x00dev->txdone_work);
+}
+
+static void rt2800usb_tx_dma_done(struct queue_entry *entry)
+{
+	struct rt2x00_dev *rt2x00dev = entry->queue->rt2x00dev;
+
+	rt2x00usb_register_read_async(rt2x00dev, TX_STA_FIFO,
+				      rt2800usb_tx_sta_fifo_read_completed);
+}
+
 /*
  * Firmware functions
  */
@@ -565,6 +594,7 @@ static int rt2800usb_probe_hw(struct rt2x00_dev *rt2x00dev)
 		__set_bit(CAPABILITY_HW_CRYPTO, &rt2x00dev->cap_flags);
 	__set_bit(CAPABILITY_LINK_TUNING, &rt2x00dev->cap_flags);
 	__set_bit(REQUIRE_HT_TX_DESC, &rt2x00dev->cap_flags);
+	__set_bit(REQUIRE_TXSTATUS_FIFO, &rt2x00dev->cap_flags);
 
 	/*
 	 * Set the rssi offset.
@@ -635,6 +665,7 @@ static const struct rt2x00lib_ops rt2800usb_rt2x00_ops = {
 	.kick_queue		= rt2x00usb_kick_queue,
 	.stop_queue		= rt2800usb_stop_queue,
 	.flush_queue		= rt2x00usb_flush_queue,
+	.tx_dma_done		= rt2800usb_tx_dma_done,
 	.write_tx_desc		= rt2800usb_write_tx_desc,
 	.write_tx_data		= rt2800usb_write_tx_data,
 	.write_beacon		= rt2800_write_beacon,

drivers/net/wireless/rt2x00/rt2x00.h

@@ -571,6 +571,7 @@ struct rt2x00lib_ops {
 	void (*kick_queue) (struct data_queue *queue);
 	void (*stop_queue) (struct data_queue *queue);
 	void (*flush_queue) (struct data_queue *queue);
+	void (*tx_dma_done) (struct queue_entry *entry);
 
 	/*
 	 * TX control handlers

drivers/net/wireless/rt2x00/rt2x00usb.c

@@ -165,6 +165,56 @@ int rt2x00usb_regbusy_read(struct rt2x00_dev *rt2x00dev,
 }
 EXPORT_SYMBOL_GPL(rt2x00usb_regbusy_read);
 
+
+struct rt2x00_async_read_data {
+	__le32 reg;
+	struct usb_ctrlrequest cr;
+	struct rt2x00_dev *rt2x00dev;
+	void (*callback)(struct rt2x00_dev *,int,u32);
+};
+
+static void rt2x00usb_register_read_async_cb(struct urb *urb)
+{
+	struct rt2x00_async_read_data *rd = urb->context;
+	rd->callback(rd->rt2x00dev, urb->status, le32_to_cpu(rd->reg));
+	kfree(urb->context);
+}
+
+void rt2x00usb_register_read_async(struct rt2x00_dev *rt2x00dev,
+				   const unsigned int offset,
+				   void (*callback)(struct rt2x00_dev*,int,u32))
+{
+	struct usb_device *usb_dev = to_usb_device_intf(rt2x00dev->dev);
+	struct urb *urb;
+	struct rt2x00_async_read_data *rd;
+
+	rd = kmalloc(sizeof(*rd), GFP_ATOMIC);
+	if (!rd)
+		return;
+
+	urb = usb_alloc_urb(0, GFP_ATOMIC);
+	if (!urb) {
+		kfree(rd);
+		return;
+	}
+
+	rd->rt2x00dev = rt2x00dev;
+	rd->callback = callback;
+	rd->cr.bRequestType = USB_VENDOR_REQUEST_IN;
+	rd->cr.bRequest = USB_MULTI_READ;
+	rd->cr.wValue = 0;
+	rd->cr.wIndex = cpu_to_le16(offset);
+	rd->cr.wLength = cpu_to_le16(sizeof(u32));
+
+	usb_fill_control_urb(urb, usb_dev, usb_rcvctrlpipe(usb_dev, 0),
+			     (unsigned char *)(&rd->cr), &rd->reg, sizeof(rd->reg),
+			     rt2x00usb_register_read_async_cb, rd);
+	if (usb_submit_urb(urb, GFP_ATOMIC) < 0)
+		kfree(rd);
+	usb_free_urb(urb);
+}
+EXPORT_SYMBOL_GPL(rt2x00usb_register_read_async);
+
 /*
  * TX data handlers.
  */
@@ -212,6 +262,9 @@ static void rt2x00usb_interrupt_txdone(struct urb *urb)
 	if (!test_and_clear_bit(ENTRY_OWNER_DEVICE_DATA, &entry->flags))
 		return;
 
+	if (rt2x00dev->ops->lib->tx_dma_done)
+		rt2x00dev->ops->lib->tx_dma_done(entry);
+
 	/*
 	 * Report the frame as DMA done
 	 */

drivers/net/wireless/rt2x00/rt2x00usb.h

@@ -345,6 +345,21 @@ int rt2x00usb_regbusy_read(struct rt2x00_dev *rt2x00dev,
 			   const struct rt2x00_field32 field,
 			   u32 *reg);
 
+/**
+ * rt2x00usb_register_read_async - Asynchronously read 32bit register word
+ * @rt2x00dev: Device pointer, see &struct rt2x00_dev.
+ * @offset: Register offset
+ * @callback: Functon to call when read completes.
+ *
+ * Submit a control URB to read a 32bit register. This safe to
+ * be called from atomic context.  The callback will be called
+ * when the URB completes. Otherwise the function is similar
+ * to rt2x00usb_register_read().
+ */
+void rt2x00usb_register_read_async(struct rt2x00_dev *rt2x00dev,
+				   const unsigned int offset,
+				   void (*callback)(struct rt2x00_dev*,int,u32));
+
 /*
  * Radio handlers
  */