Similar to the commit 1161db6776bd ("media: usb: pwc: Don't use coherent
DMA buffers for ISO transfer") [1] for the pwc driver. Use streaming DMA
APIs to transfer buffers and sync them explicitly, because accessing
buffers allocated by usb_alloc_coherent() is slow on platforms without
hardware coherent DMA.Tested on x86-64 (Intel Celeron 4305U) and armv7l (Rockchip RK3288) with Logitech Brio 4K camera at 1920x1080 using the WebRTC sample site [3]. | | URB (us) | Decode (Gbps) | CPU (%) | |------------------|------------|---------------|---------| | x86-64 coherent | 53 +- 20 | 50.6 | 0.24 | | x86-64 streaming | 55 +- 19 | 50.1 | 0.25 | | armv7l coherent | 342 +- 379 | 1.8 | 2.16 | | armv7l streaming | 99 +- 98 | 11.0 | 0.36 | The performance characteristics are improved a lot on armv7l, and remained (almost) unchanged on x86-64. The code used for measurement can be found at [2]. [1] https://git.kernel.org/torvalds/c/1161db6776bd [2] https://crrev.com/c/1729133 [3] https://webrtc.github.io/samples/src/content/getusermedia/resolution/ Signed-off-by: Shik Chen <[email protected]> --- The allocated buffer could be as large as 768K when streaming 4K video. Ideally we should use some generic helper to allocate non-coherent memory in a more efficient way, such as https://lwn.net/Articles/774429/ ("make the non-consistent DMA allocator more userful"). But I cannot find any existing helper so a simple kzalloc() is used in this patch. The logic to figure out the DMA addressable GFP flags is similar to __dma_direct_alloc_pages() without the optimistic retries: https://elixir.bootlin.com/linux/v5.2.5/source/kernel/dma/direct.c#L96 drivers/media/usb/uvc/uvc_video.c | 65 +++++++++++++++++++++---------- 1 file changed, 45 insertions(+), 20 deletions(-) diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c index 8fa77a81dd7f2c..962c35478896c4 100644 --- a/drivers/media/usb/uvc/uvc_video.c +++ b/drivers/media/usb/uvc/uvc_video.c @@ -1539,6 +1539,8 @@ 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. */ + dma_sync_single_for_cpu(&urb->dev->dev, 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. */ @@ -1565,18 +1567,51 @@ static void uvc_free_urb_buffers(struct uvc_streaming *stream) if (!uvc_urb->buffer) continue; -#ifndef CONFIG_DMA_NONCOHERENT - usb_free_coherent(stream->dev->udev, stream->urb_size, - uvc_urb->buffer, uvc_urb->dma); -#else + dma_unmap_single(&stream->dev->udev->dev, uvc_urb->dma, + stream->urb_size, DMA_FROM_DEVICE); kfree(uvc_urb->buffer); -#endif - uvc_urb->buffer = NULL; } stream->urb_size = 0; } +static gfp_t uvc_alloc_gfp_flags(struct device *dev) +{ + u64 mask = dma_get_mask(dev); + + if (dev->bus_dma_mask) + mask &= dev->bus_dma_mask; + + if (mask < DMA_BIT_MASK(32) && IS_ENABLED(CONFIG_ZONE_DMA)) + return GFP_DMA; + + if (mask < DMA_BIT_MASK(64)) { + if (IS_ENABLED(CONFIG_ZONE_DMA32)) + return GFP_DMA32; + if (IS_ENABLED(CONFIG_ZONE_DMA)) + return GFP_DMA; + } + + return 0; +} + +static char *uvc_alloc_urb_buffer(struct device *dev, size_t size, + gfp_t gfp_flags, dma_addr_t *dma_handle) +{ + void *buffer = kzalloc(size, gfp_flags | uvc_alloc_gfp_flags(dev)); + + if (!buffer) + return NULL; + + *dma_handle = dma_map_single(dev, buffer, size, DMA_FROM_DEVICE); + if (dma_mapping_error(dev, *dma_handle)) { + kfree(buffer); + return NULL; + } + + return buffer; +} + /* * Allocate transfer buffers. This function can be called with buffers * already allocated when resuming from suspend, in which case it will @@ -1607,18 +1642,14 @@ 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, + uvc_urb->buffer = uvc_alloc_urb_buffer( + &stream->dev->udev->dev, 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) { uvc_free_urb_buffers(stream); break; @@ -1728,12 +1759,8 @@ static int uvc_init_video_isoc(struct uvc_streaming *stream, urb->context = uvc_urb; 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 = uvc_urb->dma; -#else - urb->transfer_flags = URB_ISO_ASAP; -#endif urb->interval = ep->desc.bInterval; urb->transfer_buffer = uvc_urb->buffer; urb->complete = uvc_video_complete; @@ -1793,10 +1820,8 @@ static int uvc_init_video_bulk(struct uvc_streaming *stream, usb_fill_bulk_urb(urb, stream->dev->udev, pipe, uvc_urb->buffer, size, uvc_video_complete, uvc_urb); -#ifndef CONFIG_DMA_NONCOHERENT urb->transfer_flags = URB_NO_TRANSFER_DMA_MAP; urb->transfer_dma = uvc_urb->dma; -#endif uvc_urb->urb = urb; } -- 2.22.0.770.g0f2c4a37fd-goog
