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The current implementation requires up to 3 buffers to properly implement page flipping without losing frames: one is configured before the video stream is started, one just after that and page flipping is synchronized to the frame done interrupt. The comment in the code mentions that "CSI will lookup the next dma buffer for next frame before the current frame done IRQ triggered". Based on observations of the CSI unit behavior, it seems that the buffer DMA address is sampled when the frame scan begins (in addition to starting the stream), which corresponds to the vblank interrupt that hits just before the frame-done interrupt of the previous frame. As a result, the address configured at the frame done interrupt is not actually used for the next frame but for the one after that. This proposal changes the page flipping sync point to the vsync interrupt, which allows the DMA address to be sampled for the next frame instead and allows operating with only two buffers. In addition to the change in the sync point, the code is refactored to introduce a notion of state that clarifies tracking of the buffers with tidy functions. Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com> Acked-by: Jernej Skrabec <jernej.skrabec@gmail.com> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.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.