wncm14a2a modem should be moved to a shield configuration

[nashif]

The modem is part of a shield, currently is hardcoded into the frdm_k64f board DTS. We should move it to a shield an make it available to other boards.

[mike-scott]

@nashif agreed. This is on my TODO list

[mike-scott]

@erwango What is your recommendation for establishing digital pin exports from the main board in DTS?

Under non-shield configuration:

       wncm14a2a {
               compatible = "wnc,m14a2a";
               label = "wncm14a2a";
               mdm-boot-mode-sel-gpios = <&gpioc 17 0>;
               mdm-power-gpios = <&gpiob 9 0>;
               mdm-keep-awake-gpios = <&gpioc 2 0>;
               mdm-reset-gpios = <&gpioc 12 0>;
               mdm-shld-trans-ena-gpios = <&gpioc 4 0>;
               mdm-send-ok-gpios = <&gpiod 0 0>;
               status = "ok";
       };

These should be exported in some way from the main board's DTS (note this doesn't work):

arduino_d10: <&gpiod 0 0>; {};
arduino_d9: <&gpioc 4 0>; {};
arduino_d8: <&gpioc 12 0>; {};
arduino_d6: <&gpioc 2 0>; {};
arduino_d2: <&gpiob 9 0>; {};
arduino_d1: <&gpioc 17 0>; {};

[erwango]

@mike-scott

There were on going work on dtc to enable similar stuff (https://elinux.org/images/d/d0/Panto.pdf) , but I don't know current status. I'll check on dtc status and come back to you.

There are some ways to get dtc compiled and have something like (in dts_compiled file). For instance:

arduino_spi: &spi1 {

	arduino_dx: pin {
		 gpios = <&gpioa 8 0>;
	 };

Would compile into

		arduino_spi: spi1: spi@40013000 {
			[...]
			arduino_dx: pin {
				gpios = <0x5 0x8 0x0>;
				phandle = <0x6>;
			};

			bt0: spbtle-rf@0 {
				[...]
				reset-gpios = <0x6>;
			};
		};

But then it requires some hack in extract_dts_include script to do the last step, would be better to have this done in dtc. So this would work, but would be a divergence from Linux. It seems we are a the edge of the dtc features here... Maybe @galak you have more inputs?
So either we chose our on way, waiting to have things integrated (maybe in a different way) in Linux, either we wait Linux. Let's check last dtc status before going further.