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The SPI chipselects are assumed to be active low in the current binding, so when we want to use GPIO descriptors and handle the active low/high semantics in gpiolib, we need a special parsing quirk to deal with this. We check for the property "spi-cs-high" and if that is NOT present we assume the CS line is active low. If the line is tagged as active low in the device tree and has no "spi-cs-high" property all is fine, the device tree and the SPI bindings are in agreement. If the line is tagged as active high in the device tree with the second cell flag and has no "spi-cs-high" property we enforce active low semantics (as this is the exception we can just tag on the flag). If the line is tagged as active low with the second cell flag AND tagged with "spi-cs-high" the SPI active high property takes precedence and we print a warning. Cc: Mark Brown <broonie@kernel.org> Cc: linux-spi@vger.kernel.org Cc: Geert Uytterhoeven <geert@linux-m68k.org> Signed-off-by: Linus Walleij <linus.walleij@linaro.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.