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The function of each SoM pins is defined in the DHCOM standard [1] and subset of them is defined as GPIOs (pins A-W). To ensure the interchange- ability of the DHCOM SoMs, the function of the pins are fixed and cannot be changed. On board level the DHCOM GPIOs can be used associated with different blocks e.g. for interrupt or reset, but the function is always GPIO. If not used, they can be freely used in the user space. Therefore the whole configuration of SoM pins is made in the SoM DT. Defining the DHCOM GPIO pins as a separate pinctrl nodes makes moving a subset of them to an appropriate block pinctrl group easier on board level, since it is not necessary to have a large pinctrl hog group containing unrelated pinmux entries on board level. This also makes it easy to update the SoM DT without having to update all the board DTs too. If necessary it is also possible to change the electrical properties of the DHCOM GPIOs by overwriting the pinctrl on board level. [1] https://wiki.dh-electronics.com/images/2/2e/DOC_DHCOM-Standard-Specification_R01_2016-11-17.pdf Signed-off-by: Christoph Niedermaier <cniedermaier@dh-electronics.com> Cc: Shawn Guo <shawnguo@kernel.org> Cc: Fabio Estevam <festevam@denx.de> Cc: Marek Vasut <marex@denx.de> Cc: NXP Linux Team <linux-imx@nxp.com> Cc: kernel@dh-electronics.com To: linux-arm-kernel@lists.infradead.org Signed-off-by: Shawn Guo <shawnguo@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.