media: uvcvideo: Move decode processing to process context

Newer high definition cameras, and cameras with multiple lenses such as
the range of stereo-vision cameras now available have ever increasing
data rates.

The inclusion of a variable length packet header in URB packets mean
that we must memcpy the frame data out to our destination 'manually'.
This can result in data rates of up to 2 gigabits per second being
processed.

To improve efficiency, and maximise throughput, handle the URB decode
processing through a work queue to move it from interrupt context, and
allow multiple processors to work on URBs in parallel.

Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
index afb44d1..b62cbd8 100644 (file)
--- a/drivers/media/usb/uvc/uvc_driver.c
+++ b/drivers/media/usb/uvc/uvc_driver.c
@@ -401,6 +401,9 @@ static struct uvc_streaming *uvc_stream_by_id(struct uvc_device *dev, int id)
 
 static void uvc_stream_delete(struct uvc_streaming *stream)
 {
+       if (stream->async_wq)
+               destroy_workqueue(stream->async_wq);
+
        mutex_destroy(&stream->mutex);
 
        usb_put_intf(stream->intf);
@@ -425,6 +428,14 @@ static struct uvc_streaming *uvc_stream_new(struct uvc_device *dev,
        stream->intf = usb_get_intf(intf);
        stream->intfnum = intf->cur_altsetting->desc.bInterfaceNumber;
 
+       /* Allocate a stream specific work queue for asynchronous tasks. */
+       stream->async_wq = alloc_workqueue("uvcvideo", WQ_UNBOUND | WQ_HIGHPRI,
+                                          0);
+       if (!stream->async_wq) {
+               uvc_stream_delete(stream);
+               return NULL;
+       }
+
        return stream;
 }
 

diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
index 7a7779e..e19bdf0 100644 (file)
--- a/drivers/media/usb/uvc/uvc_video.c
+++ b/drivers/media/usb/uvc/uvc_video.c
@@ -1094,21 +1094,54 @@ static int uvc_video_decode_start(struct uvc_streaming *stream,
        return data[0];
 }
 
-static void uvc_video_decode_data(struct uvc_streaming *stream,
+/*
+ * uvc_video_decode_data_work: Asynchronous memcpy processing
+ *
+ * Copy URB data to video buffers in process context, releasing buffer
+ * references and requeuing the URB when done.
+ */
+static void uvc_video_copy_data_work(struct work_struct *work)
+{
+       struct uvc_urb *uvc_urb = container_of(work, struct uvc_urb, work);
+       unsigned int i;
+       int ret;
+
+       for (i = 0; i < uvc_urb->async_operations; i++) {
+               struct uvc_copy_op *op = &uvc_urb->copy_operations[i];
+
+               memcpy(op->dst, op->src, op->len);
+
+               /* Release reference taken on this buffer. */
+               uvc_queue_buffer_release(op->buf);
+       }
+
+       ret = usb_submit_urb(uvc_urb->urb, GFP_KERNEL);
+       if (ret < 0)
+               uvc_printk(KERN_ERR, "Failed to resubmit video URB (%d).\n",
+                          ret);
+}
+
+static void uvc_video_decode_data(struct uvc_urb *uvc_urb,
                struct uvc_buffer *buf, const u8 *data, int len)
 {
-       unsigned int maxlen, nbytes;
-       void *mem;
+       unsigned int active_op = uvc_urb->async_operations;
+       struct uvc_copy_op *op = &uvc_urb->copy_operations[active_op];
+       unsigned int maxlen;
 
        if (len <= 0)
                return;
 
-       /* Copy the video data to the buffer. */
        maxlen = buf->length - buf->bytesused;
-       mem = buf->mem + buf->bytesused;
-       nbytes = min((unsigned int)len, maxlen);
-       memcpy(mem, data, nbytes);
-       buf->bytesused += nbytes;
+
+       /* Take a buffer reference for async work. */
+       kref_get(&buf->ref);
+
+       op->buf = buf;
+       op->src = data;
+       op->dst = buf->mem + buf->bytesused;
+       op->len = min_t(unsigned int, len, maxlen);
+
+       buf->bytesused += op->len;
 
        /* Complete the current frame if the buffer size was exceeded. */
        if (len > maxlen) {
@@ -1116,6 +1149,8 @@ static void uvc_video_decode_data(struct uvc_streaming *stream,
                buf->error = 1;
                buf->state = UVC_BUF_STATE_READY;
        }
+
+       uvc_urb->async_operations++;
 }
 
 static void uvc_video_decode_end(struct uvc_streaming *stream,
@@ -1324,7 +1359,7 @@ static void uvc_video_decode_isoc(struct uvc_urb *uvc_urb,
                uvc_video_decode_meta(stream, meta_buf, mem, ret);
 
                /* Decode the payload data. */
-               uvc_video_decode_data(stream, buf, mem + ret,
+               uvc_video_decode_data(uvc_urb, buf, mem + ret,
                        urb->iso_frame_desc[i].actual_length - ret);
 
                /* Process the header again. */
@@ -1384,9 +1419,9 @@ static void uvc_video_decode_bulk(struct uvc_urb *uvc_urb,
         * sure buf is never dereferenced if NULL.
         */
 
-       /* Process video data. */
+       /* Prepare video data for processing. */
        if (!stream->bulk.skip_payload && buf != NULL)
-               uvc_video_decode_data(stream, buf, mem, len);
+               uvc_video_decode_data(uvc_urb, buf, mem, len);
 
        /* Detect the payload end by a URB smaller than the maximum size (or
         * a payload size equal to the maximum) and process the header again.
@@ -1472,7 +1507,7 @@ static void uvc_video_complete(struct urb *urb)
                uvc_printk(KERN_WARNING, "Non-zero status (%d) in video "
                        "completion handler.\n", urb->status);
                /* fall through */
-       case -ENOENT:           /* usb_kill_urb() called. */
+       case -ENOENT:           /* usb_poison_urb() called. */
                if (stream->frozen)
                        return;
                /* fall through */
@@ -1494,12 +1529,26 @@ static void uvc_video_complete(struct urb *urb)
                spin_unlock_irqrestore(&qmeta->irqlock, flags);
        }
 
+       /* Re-initialise the URB async work. */
+       uvc_urb->async_operations = 0;
+
+       /*
+        * Process the URB headers, and optionally queue expensive memcpy tasks
+        * to be deferred to a work queue.
+        */
        stream->decode(uvc_urb, buf, buf_meta);
 
-       if ((ret = usb_submit_urb(urb, GFP_ATOMIC)) < 0) {
-               uvc_printk(KERN_ERR, "Failed to resubmit video URB (%d).\n",
-                       ret);
+       /* If no async work is needed, resubmit the URB immediately. */
+       if (!uvc_urb->async_operations) {
+               ret = usb_submit_urb(uvc_urb->urb, GFP_ATOMIC);
+               if (ret < 0)
+                       uvc_printk(KERN_ERR,
+                                  "Failed to resubmit video URB (%d).\n",
+                                  ret);
+               return;
        }
+
+       queue_work(stream->async_wq, &uvc_urb->work);
 }
 
 /*
@@ -1594,20 +1643,22 @@ static int uvc_alloc_urb_buffers(struct uvc_streaming *stream,
  */
 static void uvc_uninit_video(struct uvc_streaming *stream, int free_buffers)
 {
-       struct urb *urb;
-       unsigned int i;
+       struct uvc_urb *uvc_urb;
 
        uvc_video_stats_stop(stream);
 
-       for (i = 0; i < UVC_URBS; ++i) {
-               struct uvc_urb *uvc_urb = &stream->uvc_urb[i];
+       /*
+        * We must poison the URBs rather than kill them to ensure that even
+        * after the completion handler returns, any asynchronous workqueues
+        * will be prevented from resubmitting the URBs.
+        */
+       for_each_uvc_urb(uvc_urb, stream)
+               usb_poison_urb(uvc_urb->urb);
 
-               urb = uvc_urb->urb;
-               if (urb == NULL)
-                       continue;
+       flush_workqueue(stream->async_wq);
 
-               usb_kill_urb(urb);
-               usb_free_urb(urb);
+       for_each_uvc_urb(uvc_urb, stream) {
+               usb_free_urb(uvc_urb->urb);
                uvc_urb->urb = NULL;
        }
 
@@ -1932,6 +1983,7 @@ int uvc_video_init(struct uvc_streaming *stream)
        struct uvc_streaming_control *probe = &stream->ctrl;
        struct uvc_format *format = NULL;
        struct uvc_frame *frame = NULL;
+       struct uvc_urb *uvc_urb;
        unsigned int i;
        int ret;
 
@@ -2017,6 +2069,10 @@ int uvc_video_init(struct uvc_streaming *stream)
                }
        }
 
+       /* Prepare asynchronous work items. */
+       for_each_uvc_urb(uvc_urb, stream)
+               INIT_WORK(&uvc_urb->work, uvc_video_copy_data_work);
+
        return 0;
 }
 

diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
index 92a17f0..c7e96d5 100644 (file)
--- a/drivers/media/usb/uvc/uvcvideo.h
+++ b/drivers/media/usb/uvc/uvcvideo.h
@@ -494,12 +494,30 @@ struct uvc_stats_stream {
 #define UVC_METATADA_BUF_SIZE 1024
 
 /**
+ * struct uvc_copy_op: Context structure to schedule asynchronous memcpy
+ *
+ * @buf: active buf object for this operation
+ * @dst: copy destination address
+ * @src: copy source address
+ * @len: copy length
+ */
+struct uvc_copy_op {
+       struct uvc_buffer *buf;
+       void *dst;
+       const __u8 *src;
+       size_t len;
+};
+
+/**
  * struct uvc_urb - URB context management structure
  *
  * @urb: the URB described by this context structure
  * @stream: UVC streaming context
  * @buffer: memory storage for the URB
  * @dma: DMA coherent addressing for the urb_buffer
+ * @async_operations: counter to indicate the number of copy operations
+ * @copy_operations: work descriptors for asynchronous copy operations
+ * @work: work queue entry for asynchronous decode
  */
 struct uvc_urb {
        struct urb *urb;
@@ -507,6 +525,10 @@ struct uvc_urb {
 
        char *buffer;
        dma_addr_t dma;
+
+       unsigned int async_operations;
+       struct uvc_copy_op copy_operations[UVC_MAX_PACKETS];
+       struct work_struct work;
 };
 
 struct uvc_streaming {
@@ -539,6 +561,7 @@ struct uvc_streaming {
        /* Buffers queue. */
        unsigned int frozen : 1;
        struct uvc_video_queue queue;
+       struct workqueue_struct *async_wq;
        void (*decode)(struct uvc_urb *uvc_urb, struct uvc_buffer *buf,
                       struct uvc_buffer *meta_buf);
 
@@ -592,6 +615,11 @@ struct uvc_streaming {
        } clock;
 };
 
+#define for_each_uvc_urb(uvc_urb, uvc_streaming) \
+       for ((uvc_urb) = &(uvc_streaming)->uvc_urb[0]; \
+            (uvc_urb) < &(uvc_streaming)->uvc_urb[UVC_URBS]; \
+            ++(uvc_urb))
+
 struct uvc_device_info {
        u32     quirks;
        u32     meta_format;