V4L/DVB (13138): gspca_sq905: cleanup sq905_dostream

-Remove use of unneeded discarding variable
-Cleanup locking to only take usb_lock around access to the control
 endpoint, by no longer taking the lock around the bulk transfer
 (which takes most of the time) we can remove the msleep(1) which was
 needed to give the gspca core a chance to grab the usb_lock to signal
 us to stop.
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/gspca/sq905.c

@@ -168,18 +168,22 @@ static int sq905_ack_frame(struct gspca_dev *gspca_dev)
  *  request and read a block of data - see warning on sq905_command.
  */
 static int
-sq905_read_data(struct gspca_dev *gspca_dev, u8 *data, int size)
+sq905_read_data(struct gspca_dev *gspca_dev, u8 *data, int size, int need_lock)
 {
 	int ret;
 	int act_len;
 
 	gspca_dev->usb_buf[0] = '\0';
+	if (need_lock)
+		mutex_lock(&gspca_dev->usb_lock);
 	ret = usb_control_msg(gspca_dev->dev,
 			      usb_sndctrlpipe(gspca_dev->dev, 0),
 			      USB_REQ_SYNCH_FRAME,                /* request */
 			      USB_DIR_OUT | USB_TYPE_VENDOR | USB_RECIP_DEVICE,
 			      SQ905_BULK_READ, size, gspca_dev->usb_buf,
 			      1, SQ905_CMD_TIMEOUT);
+	if (need_lock)
+		mutex_unlock(&gspca_dev->usb_lock);
 	if (ret < 0) {
 		PDEBUG(D_ERR, "%s: usb_control_msg failed (%d)", __func__, ret);
 		return ret;
@@ -214,7 +218,6 @@ static void sq905_dostream(struct work_struct *work)
 	int bytes_left; /* bytes remaining in current frame. */
 	int data_len;   /* size to use for the next read. */
 	int header_read; /* true if we have already read the frame header. */
-	int discarding; /* true if we failed to get space for frame. */
 	int packet_type;
 	int frame_sz;
 	int ret;
@@ -222,7 +225,6 @@ static void sq905_dostream(struct work_struct *work)
 	u8 *buffer;
 
 	buffer = kmalloc(SQ905_MAX_TRANSFER, GFP_KERNEL | GFP_DMA);
-	mutex_lock(&gspca_dev->usb_lock);
 	if (!buffer) {
 		PDEBUG(D_ERR, "Couldn't allocate USB buffer");
 		goto quit_stream;
@@ -232,28 +234,22 @@ static void sq905_dostream(struct work_struct *work)
 			+ FRAME_HEADER_LEN;
 
 	while (gspca_dev->present && gspca_dev->streaming) {
-		/* Need a short delay to ensure streaming flag was set by
-		 * gspca and to make sure gspca can grab the mutex. */
-		mutex_unlock(&gspca_dev->usb_lock);
-		msleep(1);
-
 		/* request some data and then read it until we have
 		 * a complete frame. */
 		bytes_left = frame_sz;
 		header_read = 0;
-		discarding = 0;
 
-		while (bytes_left > 0) {
+		/* Note we do not check for gspca_dev->streaming here, as
+		   we must finish reading an entire frame, otherwise the
+		   next time we stream we start reading in the middle of a
+		   frame. */
+		while (bytes_left > 0 && gspca_dev->present) {
 			data_len = bytes_left > SQ905_MAX_TRANSFER ?
 				SQ905_MAX_TRANSFER : bytes_left;
-			mutex_lock(&gspca_dev->usb_lock);
-			if (!gspca_dev->present)
-				goto quit_stream;
-			ret = sq905_read_data(gspca_dev, buffer, data_len);
+			ret = sq905_read_data(gspca_dev, buffer, data_len, 1);
 			if (ret < 0)
 				goto quit_stream;
-			mutex_unlock(&gspca_dev->usb_lock);
-			PDEBUG(D_STREAM,
+			PDEBUG(D_PACK,
 				"Got %d bytes out of %d for frame",
 				data_len, bytes_left);
 			bytes_left -= data_len;
@@ -271,7 +267,7 @@ static void sq905_dostream(struct work_struct *work)
 				packet_type = INTER_PACKET;
 			}
 			frame = gspca_get_i_frame(gspca_dev);
-			if (frame && !discarding) {
+			if (frame) {
 				frame = gspca_frame_add(gspca_dev, packet_type,
 						frame, data, data_len);
 				/* If entire frame fits in one packet we still
@@ -281,23 +277,23 @@ static void sq905_dostream(struct work_struct *work)
 					frame = gspca_frame_add(gspca_dev,
 							LAST_PACKET,
 							frame, data, 0);
-			} else {
-				discarding = 1;
 			}
 		}
+		if (gspca_dev->present) {
 			/* acknowledge the frame */
 			mutex_lock(&gspca_dev->usb_lock);
-		if (!gspca_dev->present)
-			goto quit_stream;
 			ret = sq905_ack_frame(gspca_dev);
+			mutex_unlock(&gspca_dev->usb_lock);
 			if (ret < 0)
 				goto quit_stream;
 		}
+	}
 quit_stream:
-	/* the usb_lock is already acquired */
-	if (gspca_dev->present)
+	if (gspca_dev->present) {
+		mutex_lock(&gspca_dev->usb_lock);
 		sq905_command(gspca_dev, SQ905_CLEAR);
 		mutex_unlock(&gspca_dev->usb_lock);
+	}
 	kfree(buffer);
 }
 
@@ -346,7 +342,7 @@ static int sd_init(struct gspca_dev *gspca_dev)
 	ret = sq905_command(gspca_dev, SQ905_ID);
 	if (ret < 0)
 		return ret;
-	ret = sq905_read_data(gspca_dev, gspca_dev->usb_buf, 4);
+	ret = sq905_read_data(gspca_dev, gspca_dev->usb_buf, 4, 0);
 	if (ret < 0)
 		return ret;
 	/* usb_buf is allocated with kmalloc so is aligned.