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When we use an async work queue to perform the function of pumping usb requests to the usb controller, it is possible that amongst other factors, thread scheduling affects at what cadence we're able to pump requests. This could mean isoc usb requests miss their uframes - resulting in video stream flickers on the host device. To avoid this, we make the async_wq thread only produce isoc usb_requests with uvc buffers encoded into them. The process of queueing to the endpoint is done by the uvc_video_complete() handler. In case no usb_requests are ready with encoded information, we just queue a zero length request to the endpoint from the complete handler. For bulk endpoints the async_wq thread still queues usb requests to the endpoint. Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de> Signed-off-by: Jayant Chowdhary <jchowdhary@google.com> Suggested-by: Avichal Rakesh <arakesh@google.com> Suggested-by: Alan Stern <stern@rowland.harvard.edu> Link: https://lore.kernel.org/r/20231120062026.3759463-1-jchowdhary@google.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.