media: em28xx: don't use coherent buffer for DMA transfers

While coherent memory is cheap on x86, it may cause performance
impacts on other archs. As we don't have any good reason to
use it, let's change the logic by allocating memory via kmalloc()
and letting the USB core to do the DMA mapping and memory free
for us.

While here, also fixes an issue that it was not de-allocating
memories if something gets wrong during memory block
allocation.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/usb/em28xx/em28xx-core.c

@@ -821,7 +821,6 @@ void em28xx_uninit_usb_xfer(struct em28xx *dev, enum em28xx_mode mode)
 {
 	struct urb *urb;
 	struct em28xx_usb_bufs *usb_bufs;
-	struct usb_device *udev = interface_to_usbdev(dev->intf);
 	int i;
 
 	em28xx_isocdbg("em28xx: called em28xx_uninit_usb_xfer in mode %d\n",
@@ -840,23 +839,16 @@ void em28xx_uninit_usb_xfer(struct em28xx *dev, enum em28xx_mode mode)
 			else
 				usb_unlink_urb(urb);
 
-			if (usb_bufs->transfer_buffer[i]) {
-				usb_free_coherent(udev,
-						  urb->transfer_buffer_length,
-						  usb_bufs->transfer_buffer[i],
-						  urb->transfer_dma);
-			}
 			usb_free_urb(urb);
 			usb_bufs->urb[i] = NULL;
 		}
-		usb_bufs->transfer_buffer[i] = NULL;
 	}
 
 	kfree(usb_bufs->urb);
-	kfree(usb_bufs->transfer_buffer);
+	kfree(usb_bufs->buf);
 
 	usb_bufs->urb = NULL;
-	usb_bufs->transfer_buffer = NULL;
+	usb_bufs->buf = NULL;
 	usb_bufs->num_bufs = 0;
 
 	em28xx_capture_start(dev, 0);
@@ -933,14 +925,13 @@ int em28xx_alloc_urbs(struct em28xx *dev, enum em28xx_mode mode, int xfer_bulk,
 
 	usb_bufs->num_bufs = num_bufs;
 
-	usb_bufs->urb = kzalloc(sizeof(void *)*num_bufs,  GFP_KERNEL);
+	usb_bufs->urb = kcalloc(sizeof(void *), num_bufs,  GFP_KERNEL);
 	if (!usb_bufs->urb)
 		return -ENOMEM;
 
-	usb_bufs->transfer_buffer = kzalloc(sizeof(void *)*num_bufs,
-					     GFP_KERNEL);
-	if (!usb_bufs->transfer_buffer) {
-		kfree(usb_bufs->urb);
+	usb_bufs->buf = kcalloc(sizeof(void *), num_bufs, GFP_KERNEL);
+	if (!usb_bufs->buf) {
+		kfree(usb_bufs->buf);
 		return -ENOMEM;
 	}
 
@@ -963,37 +954,41 @@ int em28xx_alloc_urbs(struct em28xx *dev, enum em28xx_mode mode, int xfer_bulk,
 		}
 		usb_bufs->urb[i] = urb;
 
-		usb_bufs->transfer_buffer[i] = usb_alloc_coherent(udev,
-			sb_size, GFP_KERNEL, &urb->transfer_dma);
-		if (!usb_bufs->transfer_buffer[i]) {
+		usb_bufs->buf[i] = kzalloc(sb_size, GFP_KERNEL);
+		if (!usb_bufs->buf[i]) {
 			dev_err(&dev->intf->dev,
 				"unable to allocate %i bytes for transfer buffer %i%s\n",
 			       sb_size, i,
 			       in_interrupt() ? " while in int" : "");
+
 			em28xx_uninit_usb_xfer(dev, mode);
+
+			for (i--; i >= 0; i--)
+				kfree(usb_bufs->buf[i]);
+
+			kfree(usb_bufs->buf);
+			usb_bufs->buf = NULL;
+
 			return -ENOMEM;
 		}
-		memset(usb_bufs->transfer_buffer[i], 0, sb_size);
+
+		urb->transfer_flags = URB_FREE_BUFFER;
 
 		if (xfer_bulk) { /* bulk */
 			pipe = usb_rcvbulkpipe(udev,
 					       mode == EM28XX_ANALOG_MODE ?
 					       dev->analog_ep_bulk :
 					       dev->dvb_ep_bulk);
-			usb_fill_bulk_urb(urb, udev, pipe,
-					  usb_bufs->transfer_buffer[i], sb_size,
-					  em28xx_irq_callback, dev);
-			urb->transfer_flags = URB_NO_TRANSFER_DMA_MAP;
+			usb_fill_bulk_urb(urb, udev, pipe, usb_bufs->buf[i],
+					  sb_size, em28xx_irq_callback, dev);
 		} else { /* isoc */
 			pipe = usb_rcvisocpipe(udev,
 					       mode == EM28XX_ANALOG_MODE ?
 					       dev->analog_ep_isoc :
 					       dev->dvb_ep_isoc);
-			usb_fill_int_urb(urb, udev, pipe,
-					 usb_bufs->transfer_buffer[i], sb_size,
-					 em28xx_irq_callback, dev, 1);
-			urb->transfer_flags = URB_ISO_ASAP |
-					      URB_NO_TRANSFER_DMA_MAP;
+			usb_fill_int_urb(urb, udev, pipe, usb_bufs->buf[i],
+					 sb_size, em28xx_irq_callback, dev, 1);
+			urb->transfer_flags |= URB_ISO_ASAP;
 			k = 0;
 			for (j = 0; j < usb_bufs->num_packets; j++) {
 				urb->iso_frame_desc[j].offset = k;

drivers/media/usb/em28xx/em28xx.h

@@ -242,7 +242,7 @@ struct em28xx_usb_bufs {
 	struct urb			**urb;
 
 		/* transfer buffers for isoc/bulk transfer */
-	char				**transfer_buffer;
+	char				**buf;
 };
 
 struct em28xx_usb_ctl {