Hello Bin,

I would like to start new thread on my issue. Let me recall where the issue is:
There is 100% frame lost in pwc webcam driver due to lots of
zero-length packages coming from musb driver.
The issue is present in all kernels (including 4.8) starting from the commit:

f551e13529833e052f75ec628a8af7b034af20f9 ("Revert "usb: musb:
musb_host: Enable HCD_BH flag to handle urb return in bottom half"")

The issue is here both when DMA enabled and DMA disabled.

Attached here is a plot. The vertical axis designates the value of
rx_count variable from function musb_host_packet_rx(). One may see
that there are only two possibilities: 0 bytes and 956 bytes.
The horizontal axis is the last three digits of the timestamp when
musb_host_packet_rx() invoked. I.e for [   38.115379] it is 379. Given
that my webcam is USB 1.1 and base time is 1 ms, then all frames
should be grouped close to some single value. (Repeating package
receive event every 1 ms won't change last tree digits considerably)
One may see that it is not true, in practice there are two groups. And
receive time strongly correlates with the package size. Packages
received near round ms are 956 bytes long, packages received near 400
us are 0 bytes long.

I don't know how exactly SOF and IN are synchronized in musb, could
someone give a hint? But from what I see the time difference between
subsequent IN package requests is sometimes more than 1 ms due to
heavy urb->complete() callback. After such events only zero length
packages are received. Surprisingly, that `synchronization' is
recovered sometimes in the middle of URB like the following:

[  163.207363] musb int
[  163.207380] rx_count 0
[  163.207393] req pkt c9c76200 // Expected musb int at 163.208393
[  163.207403] int end
// No interrupt at 163.208393
[  163.209001] musb int
[  163.209017] rx_count 956
[  163.209108] req pkt c9c76200
[  163.209118] int end

And then the series of 956 bytes long packages are received until URB
giveback will occasionally break it again.
Do I understand correctly, that SOF is generated every 1 ms by
hardware and should be followed by IN immediately?
If so, it is not clear to me how they should be aligned when the time
difference between to subsequent INs is greater than 1ms.

-- 
With best regards,
Matwey V. Kornilov.
Sternberg Astronomical Institute, Lomonosov Moscow State University, Russia
119991, Moscow, Universitetsky pr-k 13, +7 (495) 9392382