[Bug 220748] usb: xhci_queue_isoc_tx_prepare ignore start_frame and always assumes URB_ISO_ASAP is set

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=220748

--- Comment #17 from Michał Pecio (michal.pecio@gmail.com) ---
Created attachment 308930
  --> https://bugzilla.kernel.org/attachment.cgi?id=308930&action=edit
schedule isoc packets sequentially on CFC

This is a test patch which knocks out the problematic code and adds some
debugging on CFC controllers - interrupts are enabled on *all* packets, even if
the URB isn't done yet, and for each packet we check if its completion is
handled in the expected microframe. This may show false positives (the packet
moved as intended, but IRQ is handled later) but it would also catch cases when
HW executes (or reports execution) of a packet later than expected.

For example, it warns about every single packet for full speed devices behind
high speed hubs on my ASMedia controllers. Don't do it ;)

It needs a fair bit of testing to see if this approach is feasible and I still
see remaining issues in some tests (which may be due to xhci-hcd or
snd-usb-audio) but it seems to work generally better than unpatched driver.

May or may not help with Motu devices, I don't know what exactly goes wrong
with them. And again, for now, only CFC is expected to be scheduled accurately.

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