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The CSI hardware compatible with this driver handles buffers using a ping-pong mechanism with two sets of destination addresses. Normally, when an interrupt comes in to signal the completion of one buffer, say FB1, it assigns the next buffer in the queue to the next FB1, and the hardware starts to capture into FB2 in the meantime. In a buffer underrun situation, in the above example without loss of generality, if a new buffer is queued before the interrupt for FB1 comes in, we can program the buffer into FB2 (which is programmed with a dummy buffer, as there is a buffer underrun). This of course races with the interrupt that signals FB1 completion, as once that interrupt comes in, we are no longer guaranteed that the programming of FB2 was in time and must assume it was too late. This race is resolved partly by locking the programming of FB2. If it came after the interrupt for FB1, then the variable that is used to determine which FB to program would have been swapped by the interrupt handler. This alone isn't sufficient, however, because the interrupt could still be generated (thus the hardware starts capturing into the other fb) while the fast-tracking routine has the irq lock. Thus, after programming the fb register to fast-track the buffer, the isr also must be checked to confirm that an interrupt didn't come in the meantime. If it has, we must assume that programming the register for the fast-tracked buffer was not in time, and queue the buffer normally. Signed-off-by: Paul Elder <paul.elder@ideasonboard.com> Acked-by: Rui Miguel Silva <rmfrfs@gmail.com> Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.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.