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As the first frame in "repeat-mode" is the pattern, the pattern done interrupt is ignored by the driver. With small resolution bitstreams, the interrupts might fire too quickly and hardware combine two irqs to once because irq handle have latency. Thus the driver might miss the frame decode done interrupt from the first actual frame. In order to avoid the driver wait for the frame done interrupt that has been combined to the pattern done interrupt and been ignored, driver will check the curr_desc and slot_status registers to figure out if the decoding of actual frame is finished or not. Firstly we check the curr_desc register, - if it is still pointing to the pattern descriptor, the second actual frame is not started, we can wait for its frame-done interrupt. - if the curr_desc has pointed to the frame descriptor, then we check the ongoing bit of slot_status register. - if the ongoing bit is set to 1, the decoding of the actual frame is not finished, we can wait for its frame-done interrupt. - if the ongoing bit is set to 0, the decoding of the actual frame is finished, we can't wait for the second interrupt, but mark it as done. But there is still a small problem, that the curr_desc and slot_status registers are not synchronous. curr_desc is updated when the next_descpt_ptr is loaded, but the ongoing bit of slot_status is set after the 32 bytes descriptor is loaded, there will be a short time interval in between, which may cause fake false. Consider read register is quite slow compared with IP read 32byte from memory, read twice slot_status can avoid this situation. Signed-off-by: Ming Qian <ming.qian@oss.nxp.com> Reviewed-by: Frank Li <Frank.Li@nxp.com> Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com> Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
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 reStructuredText 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.