UPSTREAM: usb: gadget: uvc: queue empty isoc requests if no video buffer is available

ISOC transfers expect a certain cadence of requests being queued. Not
keeping up with the expected rate of requests results in missed ISOC
transfers (EXDEV). The application layer may or may not produce video
frames to match this expectation, so uvc gadget driver must handle cases
where the application is not queuing up buffers fast enough to fulfill
ISOC requirements.

Currently, uvc gadget driver waits for new video buffer to become available
before queuing up usb requests. With this patch the gadget driver queues up
0 length usb requests whenever there are no video buffers available. The
USB controller's complete callback is used as the limiter for how quickly
the 0 length packets will be queued. Video buffers are still queued as
soon as they become available.

Link: https://lore.kernel.org/CAMHf4WKbi6KBPQztj9FA4kPvESc1fVKrC8G73-cs6tTeQby9=w@mail.gmail.com/


Change-Id: Id437031d9ecdcda0911e4c573eaac134953c1fc3
Signed-off-by: Avichal Rakesh <arakesh@google.com>
Link: https://lore.kernel.org/r/20230508231103.1621375-1-arakesh@google.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

(cherry picked from commit c3ff12a9)
Bug: 271684194
Change-Id: I3eed9b415f80ccea9c69b0d96593da8493dbf6bb
Signed-off-by: Avichal Rakesh <arakesh@google.com>