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Commit 3e0ac671 authored by Al Cooper's avatar Al Cooper Committed by Mauro Carvalho Chehab
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[media] media: Fix a UVC performance problem on systems with non-coherent DMA 



The UVC driver uses usb_alloc_coherent() to allocate DMA data buffers.
On systems without coherent DMA this ends up allocating buffers in
uncached memory. The subsequent memcpy's done to coalesce the DMA
chunks into contiguous buffers then run VERY slowly. On a MIPS test
system the memcpy is about 200 times slower. This issue prevents the
system from keeping up with 720p YUYV data at 10fps.

The following patch uses kmalloc to alloc the DMA buffers instead of
usb_alloc_coherent on systems without coherent DMA. With this patch
the system was easily able to keep up with 720p at 10fps.

Signed-off-by: default avatarAl Cooper <alcooperx@gmail.com>
Acked-by: default avatarLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: default avatarMauro Carvalho Chehab <mchehab@redhat.com>
parent 227bd5b3

drivers/media/video/uvc/uvc_video.c

+16 −1
Original line number Diff line number Diff line
@@ -790,8 +790,12 @@ static void uvc_free_urb_buffers(struct uvc_streaming *stream) 


	for (i = 0; i < UVC_URBS; ++i) {

		if (stream->urb_buffer[i]) {

#ifndef CONFIG_DMA_NONCOHERENT

			usb_free_coherent(stream->dev->udev, stream->urb_size,

				stream->urb_buffer[i], stream->urb_dma[i]);

#else

			kfree(stream->urb_buffer[i]);

#endif

			stream->urb_buffer[i] = NULL;

		}

	}
@@ -831,9 +835,14 @@ static int uvc_alloc_urb_buffers(struct uvc_streaming *stream, 
	for (; npackets > 1; npackets /= 2) {

		for (i = 0; i < UVC_URBS; ++i) {

			stream->urb_size = psize * npackets;

#ifndef CONFIG_DMA_NONCOHERENT

			stream->urb_buffer[i] = usb_alloc_coherent(

				stream->dev->udev, stream->urb_size,

				gfp_flags | __GFP_NOWARN, &stream->urb_dma[i]);

#else

			stream->urb_buffer[i] =

			    kmalloc(stream->urb_size, gfp_flags | __GFP_NOWARN);

#endif

			if (!stream->urb_buffer[i]) {

				uvc_free_urb_buffers(stream);

				break;
@@ -908,10 +917,14 @@ static int uvc_init_video_isoc(struct uvc_streaming *stream, 
		urb->context = stream;

		urb->pipe = usb_rcvisocpipe(stream->dev->udev,

				ep->desc.bEndpointAddress);

#ifndef CONFIG_DMA_NONCOHERENT

		urb->transfer_flags = URB_ISO_ASAP | URB_NO_TRANSFER_DMA_MAP;

		urb->transfer_dma = stream->urb_dma[i];

#else

		urb->transfer_flags = URB_ISO_ASAP;

#endif

		urb->interval = ep->desc.bInterval;

		urb->transfer_buffer = stream->urb_buffer[i];

		urb->transfer_dma = stream->urb_dma[i];

		urb->complete = uvc_video_complete;

		urb->number_of_packets = npackets;

		urb->transfer_buffer_length = size;
@@ -969,8 +982,10 @@ static int uvc_init_video_bulk(struct uvc_streaming *stream, 
		usb_fill_bulk_urb(urb, stream->dev->udev, pipe,

			stream->urb_buffer[i], size, uvc_video_complete,

			stream);

#ifndef CONFIG_DMA_NONCOHERENT

		urb->transfer_flags = URB_NO_TRANSFER_DMA_MAP;

		urb->transfer_dma = stream->urb_dma[i];

#endif



		stream->urb[i] = urb;

	}