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Buffers allocated with snd_dma_alloc_pages() will have DMA direction DMA_BIDIRECTIONAL. The trace data memory is only used for one DMA direction: DMA_FROM_DEVICE, DMA only writes there, never reads. We also need to do a sync before accessing (reading with CPU) from the trace data buffer to copy it to user space. Note: snd_dma_buffer_sync() is also used for normal playback and capture streams to make sure that the data is available for the DMA or CPU. Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com> Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com> Link: https://lore.kernel.org/r/20220310171651.249385-4-pierre-louis.bossart@linux.intel.com Signed-off-by: Mark Brown <broonie@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.