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Because the SPI controller deasserts the chip select when the TX fifo is empty (which may happen in the middle of a transfer), the CS should be handled by linux. Unfortunately, some or all of the first four chip selects are not muxable as GPIOs, depending on the SoC. There is a way to bitbang those pins by using the SPI boot controller so use it to set the chip selects. At init time, it is also necessary to give control of the SPI interface to the Designware IP. Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com> Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.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.
See Documentation/00-INDEX for a list of what is contained in each file.
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.