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On the some rockchip SOCS, some things like rk3399 specific uart2 can use multiple pins. Somewhere between the pin io-cells and the uart it seems to have some sort of switch to decide to which pin to actually route the data. +-------+ +--------+ /- GPIO4_B0 (pinmux 2) | uart2 | -- | switch | --- GPIO4_C0 (pinmux 2) +-------+ +--------+ \- GPIO4_C3 (pinmux 2) (switch selects one of the 3 pins base on the GRF_SOC_CON7[BIT0, BIT1]) The routing switch is determined by one pin of a specific group to be set to its special pinmux function. If the pinmux setting is wrong for that pin the ip block won't work correctly anyway. Signed-off-by: David Wu <david.wu@rock-chips.com> Reviewed-by: Heiko Stuebner <heiko@sntech.de> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. 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.