media: uvcvideo: Use dma_alloc_noncontiguos API

On architectures where the is no coherent caching such as ARM use the
dma_alloc_noncontiguos API and handle manually the cache flushing using
dma_sync_single().

With this patch on the affected architectures we can measure up to 20x
performance improvement in uvc_video_copy_data_work().

Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>

drivers/media/usb/uvc/uvc_video.c

@@ -1641,6 +1641,11 @@ static void uvc_video_encode_bulk(struct uvc_urb *uvc_urb,
 	urb->transfer_buffer_length = stream->urb_size - len;
 }
 
+static inline struct device *stream_to_dmadev(struct uvc_streaming *stream)
+{
+	return stream->dev->udev->bus->controller->parent;
+}
+
 static void uvc_video_complete(struct urb *urb)
 {
 	struct uvc_urb *uvc_urb = urb->context;
@@ -1693,6 +1698,11 @@ static void uvc_video_complete(struct urb *urb)
 	 * Process the URB headers, and optionally queue expensive memcpy tasks
 	 * to be deferred to a work queue.
 	 */
+	if (uvc_urb->pages)
+		dma_sync_single_for_cpu(stream_to_dmadev(stream),
+					urb->transfer_dma,
+					urb->transfer_buffer_length,
+					DMA_FROM_DEVICE);
 	stream->decode(uvc_urb, buf, buf_meta);
 
 	/* If no async work is needed, resubmit the URB immediately. */
@@ -1723,8 +1733,15 @@ static void uvc_free_urb_buffers(struct uvc_streaming *stream)
 			continue;
 
 #ifndef CONFIG_DMA_NONCOHERENT
-		usb_free_coherent(stream->dev->udev, stream->urb_size,
-				  uvc_urb->buffer, uvc_urb->dma);
+		if (uvc_urb->pages) {
+			vunmap(uvc_urb->buffer);
+			dma_free_noncontiguous(stream_to_dmadev(stream),
+					       stream->urb_size,
+					       uvc_urb->pages, uvc_urb->dma);
+		} else {
+			usb_free_coherent(stream->dev->udev, stream->urb_size,
+					  uvc_urb->buffer, uvc_urb->dma);
+		}
 #else
 		kfree(uvc_urb->buffer);
 #endif
@@ -1734,6 +1751,42 @@ static void uvc_free_urb_buffers(struct uvc_streaming *stream)
 	stream->urb_size = 0;
 }
 
+#ifndef CONFIG_DMA_NONCOHERENT
+static bool uvc_alloc_urb_buffer(struct uvc_streaming *stream, struct uvc_urb *uvc_urb,
+				 gfp_t gfp_flags)
+{
+	struct device *dma_dev = dma_dev = stream_to_dmadev(stream);
+
+	if (!dma_can_alloc_noncontiguous(dma_dev)) {
+		uvc_urb->buffer = usb_alloc_coherent(stream->dev->udev, stream->urb_size,
+						     gfp_flags | __GFP_NOWARN, &uvc_urb->dma);
+		return uvc_urb->buffer != NULL;
+	}
+
+	uvc_urb->pages = dma_alloc_noncontiguous(dma_dev, stream->urb_size,
+						 &uvc_urb->dma, gfp_flags | __GFP_NOWARN, 0);
+	if (!uvc_urb->pages)
+		return false;
+
+	uvc_urb->buffer = vmap(uvc_urb->pages, PAGE_ALIGN(stream->urb_size) >> PAGE_SHIFT,
+			       VM_DMA_COHERENT, PAGE_KERNEL);
+	if (!uvc_urb->buffer) {
+		dma_free_noncontiguous(dma_dev, stream->urb_size, uvc_urb->pages, uvc_urb->dma);
+		return false;
+	}
+
+	return true;
+}
+#else
+static bool uvc_alloc_urb_buffer(struct uvc_streaming *stream, struct uvc_urb *uvc_urb,
+				 gfp_t gfp_flags)
+{
+	uvc_urb->buffer = kmalloc(stream->urb_size, gfp_flags | __GFP_NOWARN);
+
+	return uvc_urb->buffer != NULL;
+}
+#endif
+
 /*
  * Allocate transfer buffers. This function can be called with buffers
  * already allocated when resuming from suspend, in which case it will
@@ -1764,19 +1817,11 @@ static int uvc_alloc_urb_buffers(struct uvc_streaming *stream,
 
 	/* Retry allocations until one succeed. */
 	for (; npackets > 1; npackets /= 2) {
+		stream->urb_size = psize * npackets;
 		for (i = 0; i < UVC_URBS; ++i) {
 			struct uvc_urb *uvc_urb = &stream->uvc_urb[i];
 
-			stream->urb_size = psize * npackets;
-#ifndef CONFIG_DMA_NONCOHERENT
-			uvc_urb->buffer = usb_alloc_coherent(
-				stream->dev->udev, stream->urb_size,
-				gfp_flags | __GFP_NOWARN, &uvc_urb->dma);
-#else
-			uvc_urb->buffer =
-			    kmalloc(stream->urb_size, gfp_flags | __GFP_NOWARN);
-#endif
-			if (!uvc_urb->buffer) {
+			if (!uvc_alloc_urb_buffer(stream, uvc_urb, gfp_flags)) {
 				uvc_free_urb_buffers(stream);
 				break;
 			}

drivers/media/usb/uvc/uvcvideo.h

@@ -544,6 +544,7 @@ struct uvc_urb {
 
 	char *buffer;
 	dma_addr_t dma;
+	struct page **pages;
 
 	unsigned int async_operations;
 	struct uvc_copy_op copy_operations[UVC_MAX_PACKETS];