GPIO and Pinmux device tree support for Exynos.

[Stephen Warren]

Thomas Abraham wrote at Thursday, August 11, 2011 12:09 PM:
> I did some work on the gpio and pinmux device tree support for exynos.
> I thought to discuss with you about what was done before proceeding
> further.
> 
> In the dts file, the interrupt controller node is listed as
> 
> GPA: gpio-controller at 11400000 {
> 		compatible = "samsung,exynos4-gpio-gpa0", "samsung,exynos4-gpio";
> 		#gpio-cells = <4>;
> 		gpio-controller;
> };
> 
> The meaning of the 4 cells are as below. The values of all the cells
> are set as per the exynos chip specification.
> 
> < [GPIO Pin Number]  [Pin-Mux Function Number] [Pull Up/Down Setting]
> [Driver Strength Setting] >
> 
> 
> Device nodes would include the gpio's that it would use (as in below example)
> 
> serial at 13800000 {
> 		compatible = "samsung,s5pv310-uart";
> 		reg = <0x13800000 0x100>;
> 		interrupts = <116>;
> 		gpios = <&GPA  0  2  0  2   /* Tx */
> 				&GPA  1  2  0  2>;  /* Rx */
> };

The one problem with this approach is that presumably every single driver
(e.g. for the serial port above) must look for and handle the gpios
property, whereas presumably a serial port would otherwise have no need
to deal with GPIOs.

That's probably quite a bit of work. Also, what if some pins need to be
configured for which there is no driver to parse that property?

I just recently started working on this for Tegra, and in
http://www.spinics.net/lists/arm-kernel/msg136138.html
I proposed listing all the GPIO/pinmux settings directly within the GPIO
and pinmux nodes, thus making only the GPIO and pinmux drivers responsible
for parsing them. What do you think of that idea?

Thanks.

-- 
nvpublic