Understanding the NXP i.MX6UL Pin Mux (Part 2)

In the previous post, it was noted that bit 30 needs to be set in the i.MX6UL pad config if you want to read the state of a GPIO output. Digging into this a bit more, we find the following text in the Documentation/devicetree/bindings/pinctrl/fsl,imx-pinctrl.txt file:

SION(1 << 30): Software Input On Field.
Force the selected mux mode input path no matter of MUX_MODE functionality. By default the input path is determined by functionality of the selected mux mode (regular).

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Understanding the NXP i.MX6UL Pin Mux

(note, the article is also applicable to the i.MX6ULL as these processors are very similar)

The NXP i.MX6UL application processor has a very flexible pin multiplexer, that is somewhat difficult to understand at first glance.  Most times when we’re configuring the pin mux in Linux, we modify Device Tree files, so perhaps that is the place to start.  The pin mux options for the i.MX6UL are defined in the arch/arm/boot/dts/imx6ul-pinfunc.h file.  The arguments to the macros in this file are defined as:

 * The pin function ID is a tuple of
 * <mux_reg conf_reg input_reg mux_mode input_val>

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