OMAP: Configuring CONTROL_DEVCONF0 register via DT with pinctrl

[Tony Lindgren]

* Peter Ujfalusi <peter.ujfalusi at ti.com> [120727 02:47]:
> Hello,
> 
> I need to find a solution to control 2 bits in CONTROL_DEVCONF0 on OMAP2/3 for
> McBSP1 CLKR/FSR signal routing.
> In boards using McBSP1 we might need to change bit 3 and 4 based on the audio
> setup (how the board has been wired).
> 
> So far I have come up with the following idea to handle to but not really sure
> if it is the correct way (I have taken the idea from the arm/dts: Add AM33XX
> basic pinctrl support series).

You need to also consider that CONTROL_DEVCONF0 has the MMC/SDIO module input
clock selection. So pinctrl-single binding would have to be expanded to also
support one-bit-per-mux type registers in addition to one-register-per-mux
registers. And then this could also be used for the MMC/SDIO module input clock.

> In .dtsi file of the SoC:
> 
> control_devconf0: pinmux at 48002274 {
> 	compatible = "pinctrl-single";
> 	reg = <0x48002274 4>;	/* Single register */
> 	#address-cells = <1>;
> 	#size-cells = <0>;
> 	pinctrl-single,register-width = <32>;
> 	pinctrl-single,function-mask = <0x5F>;
> };

The pinctrl-single,function-mask is for all the registers in the range,
we also need something to specify the device specific mux bits.

> In the .dts file of the board which needs to change the CLKR/FSR configuration:
> 
> &control_devconf0 {
> 	pinctrl-names = "default";
> 	pinctrl-0 = <&mcbsp1_pins>;
> 
> 	mcbsp1_pins: pinmux_mcbsp1_pins {
> 		pinctrl-single,pins = <0x00 0x18>; /* CLKR/FSR from CLKX/FSX
> 						    * pin */
> 	};
> 
> };

I think adding support for one-bit-per-mux would require adding something
like this for the binding:

 	mcbsp1_pins: pinmux_mcbsp1_pins {
		/*                   offset bits mask */
 		pinctrl-single,bits = <0x00 0x18 0x18>;
	};

As otherwise you would not know which bits to clear for alternative
named modes. Or got any better ideas?

Regards,

Tony