Re: GPIO and Pinmux device tree support for Exynos.

On Thu, Aug 11, 2011 at 01:06:19PM -0700, Stephen Warren wrote:

Thomas Abraham wrote at Thursday, August 11, 2011 12:09 PM:

quoted

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@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@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.

I think that individual driver still needs to look for gpios property
to actually use gpio with gpiolib api like gpio_request(),
gpio_direction_output() etc. no?

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?

-- 
Regards,
Shawn