duplicate requests on host side while streaming via uvcvideo gadget

[Michael Grzeschik <m.grzeschik@pengutronix.de>]

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Hi Thinh

I found some strange situation while streaming via uvc-gadget to some
usb host. It happens when some requests are missed due to higher load on
the gadget machine. In some cases some requests will reach the host
twice. In my special case, I added the following changes [1] for the
host and gadget side.

When applying the patches you will find all requests marked as errors on
the host and gadget side reported. However, the odd thing is that the
error counter on the host side will rise higher than the number of
requests we have actually marked as errornous on the gadget side. You
check the number of errors found on the host by looking in the
statistics and compare it with the numer of requests that are actually
marked with UVC_STREAM_ERR.

[1] applied hunks:

diff --git a/drivers/usb/gadget/function/uvc.h b/drivers/usb/gadget/function/uvc.h
index 6bdcf3bdd62a9..63515fc949880 100644
--- a/drivers/usb/gadget/function/uvc.h
+++ b/drivers/usb/gadget/function/uvc.h
@@ -91,6 +91,8 @@ struct uvc_video {
         struct work_struct pump;
         struct workqueue_struct *async_wq;

+       int errorcount;
+
         /* Frame parameters */
         u8 bpp;
         u32 fcc;

diff --git a/drivers/usb/gadget/function/uvc_video.c b/drivers/usb/gadget/function/uvc_video.c
index eb1f7cee4a0af..f45dd53fde7ef 100644
--- a/drivers/usb/gadget/function/uvc_video.c
+++ b/drivers/usb/gadget/function/uvc_video.c
@@ -35,6 +35,12 @@ uvc_video_encode_header(struct uvc_video *video, struct uvc_buffer *buf,

         data[1] = UVC_STREAM_EOH | video->fid;

+       if (video->queue.flags & UVC_QUEUE_DROP_INCOMPLETE) {
+               video->errorcount++;
+               printk("dropping frame! %d\n", video->errorcount);
+               data[1] |= UVC_STREAM_ERR;
+       }
+
         if (video->queue.buf_used == 0 && ts.tv_sec) {
                 /* dwClockFrequency is 48 MHz */
                 u32 pts = ((u64)ts.tv_sec * USEC_PER_SEC + ts.tv_nsec / NSEC_PER_USEC) * 48;

@@ -47,6 +47,8 @@ uvc_video_encode_header(struct uvc_video *video, struct uvc_buffer *buf,
  
                 data[1] |= UVC_STREAM_PTS;
                 put_unaligned_le32(pts, &data[pos]);
+               if (data[1] & UVC_STREAM_ERR)
+                       trace_printk("PTS: %u\n", data[pos]);
                 pos += 4;
         }
  
@@ -60,6 +62,10 @@ uvc_video_encode_header(struct uvc_video *video, struct uvc_buffer *buf,
                 data[1] |= UVC_STREAM_SCR;
                 put_unaligned_le32(stc, &data[pos]);
                 put_unaligned_le16(sof, &data[pos+4]);
+               if (data[1] & UVC_STREAM_ERR) {
+                       trace_printk("SCR: %u\n", data[pos]);
+                       trace_printk("SCR: %hu\n", data[pos+4]);
+               }
                 pos += 6;
         }
  

@@ -731,6 +734,7 @@ int uvcg_video_enable(struct uvc_video *video)
         struct usb_gadget *gadget = cdev->gadget;
         int ret;

+       video->errorcount = 0;
         if (video->ep == NULL) {
                 uvcg_info(&video->uvc->func,
                           "Video enable failed, device is uninitialized.\n");

diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
index 28dde08ec6c5d..40eafe43d1888 100644
--- a/drivers/media/usb/uvc/uvc_video.c
+++ b/drivers/media/usb/uvc/uvc_video.c
@@ -916,8 +916,24 @@ static void uvc_video_stats_decode(struct uvc_streaming *stream,
         if (len <= header_size)
                 stream->stats.frame.nb_empty++;

-       if (data[1] & UVC_STREAM_ERR)
+       if (data[1] & UVC_STREAM_ERR) {
                 stream->stats.frame.nb_errors++;
+               printk("error on uvc package!\n");
+               if (data[1] & UVC_STREAM_PTS) {
+                       printk("PTS: %u\n", data[2]);
+                       if (data[1] & UVC_STREAM_SCR) {
+                               printk("SCR: %u\n", data[6]);
+                               printk("SCR: %hu\n", data[10]);
+                       }
+               } else {
+                       if (data[1] & UVC_STREAM_SCR) {
+                               printk("SCR: %u\n", data[2]);
+                               printk("SCR: %hu\n", data[6]);
+                       }
+               }
+
+
+       }
  }

-- Host:

[ 1769.213387] error on uvc package!
[ 1769.213396] PTS: 16
[ 1769.213400] SCR: 64
[ 1769.213402] SCR: 229

[ 1769.461386] error on uvc package!
[ 1769.461394] PTS: 96
[ 1769.461398] SCR: 80
[ 1769.461401] SCR: 33

[ 1769.461405] error on uvc package! <- duplicate
[ 1769.461408] PTS: 96
[ 1769.461410] SCR: 80
[ 1769.461413] SCR: 33

[ 1769.657405] error on uvc package!
[ 1769.657442] PTS: 224
[ 1769.657449] SCR: 64
[ 1769.657453] SCR: 81

[ 1769.657460] error on uvc package! <- duplicate
[ 1769.657465] PTS: 224
[ 1769.657470] SCR: 64
[ 1769.657476] SCR: 81

[ 1779.525368] error on uvc package!
[ 1779.525374] PTS: 128
[ 1779.525378] SCR: 224
[ 1779.525380] SCR: 157

[ 1784.637359] error on uvc package!
[ 1784.637367] PTS: 0
[ 1784.637371] SCR: 208
[ 1784.637374] SCR: 89

[ 1784.825357] error on uvc package!
[ 1784.825394] PTS: 224
[ 1784.825401] SCR: 192
[ 1784.825406] SCR: 63

[ 1784.841362] error on uvc package!
[ 1784.841394] PTS: 144
[ 1784.841403] SCR: 48
[ 1784.841410] SCR: 186

[ 1784.841418] error on uvc package! <- duplicate
[ 1784.841424] PTS: 144
[ 1784.841430] SCR: 48
[ 1784.841436] SCR: 186

host$ grep errors /sys/kernel/debug/usb/uvcvideo/*/stats
/sys/kernel/debug/usb/uvcvideo/4-81-1/stats:errors:  10


-- Gadget:

[  126.826517] dropping frame! 1
[  126.829658] PTS: 16
[  126.831761] SCR: 64
[  126.833858] SCR: 229

[  127.090069] dropping frame! 2
[  127.093059] PTS: 96
[  127.095164] SCR: 80
[  127.097261] SCR: 33

[  127.288045] dropping frame! 3
[  127.291041] PTS: 224
[  127.293233] SCR: 64
[  127.295330] SCR: 81

[  137.153499] dropping frame! 4
[  137.156494] PTS: 128
[  137.158687] SCR: 224
[  137.160871] SCR: 157

[  142.265135] dropping frame! 5
[  142.268131] PTS: 0
[  142.270148] SCR: 208
[  142.272332] SCR: 89

[  142.453636] dropping frame! 6
[  142.456634] PTS: 224
[  142.458825] SCR: 192
[  142.461009] SCR: 63

[  142.469131] dropping frame! 7
[  142.472118] PTS: 144
[  142.474310] SCR: 48
[  142.476407] SCR: 186

Now I am totally unsure what could cause such error, but would expect
the issue to be somewhere in the gadget driver and the mapped trb memory
content. For the uvc_video layer, I compared and tested the enqueued
request list for duplicates but could not find any. I also reverted all
recent patches that changed request handling in the past year. I still
find these request duplicates on the host side show up.

Any Ideas?

Regards,
Michael

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