Re: duplicate requests on host side while streaming via uvcvideo gadget

[Thinh Nguyen <Thinh.Nguyen@synopsys.com>]

On Tue, Feb 06, 2024, Michael Grzeschik wrote:
> 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.

Does this only happen to some specific hosts?

Are all the data of the duplicate requests matching or just some bits of
the transfer? Were you able to confirm from some usb analyzer/sniffer
that the data out the wire is actually duplicate?

> 
> 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.
> 

[snip]

> 
> -- 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?
> 

I'm not familiar with UVC, can you give more context on your validation
and error count? What's PTS/SCR? Is the device sending some error status
back as new request whenever there's -EXDEV?

Thanks,
Thinh