Re: doubt about where to put pin-mux in MX28 based platform DT

[Hector Palacios <hector.palacios-i7dp0qKlBMg@public.gmane.org>]

Hello Maxime,

On 03/07/2013 02:06 PM, Maxime Ripard wrote:
> Hi Hector,
>
> Le 06/03/2013 18:02, Hector Palacios a écrit :
>> I'm creating the DT for a custom platform based on Freescale MX28 CPU
>> and I have some doubts about where to add some pin mux configurations:
>> whether in imx28.dtsi or in my platform dts.
>>
>> A pair of examples folow:
>>
>> Example #1. My platform is using a valid IOMUX for DUART TX/RX lines
>> which is not covered in imx28.dtsi, namely the I2C0 pins. Since this is
>> a valid IOMUX that can be used by other platforms, I'd say I should
>> included it in imx28.dtsi:
>>
>> diff --git a/arch/arm/boot/dts/imx28.dtsi b/arch/arm/boot/dts/imx28.dtsi
>> index 3fa6d19..8928b7b 100644
>> --- a/arch/arm/boot/dts/imx28.dtsi
>> +++ b/arch/arm/boot/dts/imx28.dtsi
>> @@ -186,6 +186,17 @@
>>                                          fsl,pull-up = <0>;
>>                                  };
>>
>> +                               duart_pins_c: duart@2 {
>> +                                       reg = <2>;
>> +                                       fsl,pinmux-ids = <
>> +                                               0x3182 /*
>> MX28_PAD_I2C0_SCL__DUART_RX */
>> +                                               0x3192 /*
>> MX28_PAD_I2C0_SDA__DUART_TX */
>> +                                       >;
>> +                                       fsl,drive-strength = <0>;
>> +                                       fsl,voltage = <1>;
>> +                                       fsl,pull-up = <0>;
>> +                               };
>> +
>>                                  duart_4pins_a: duart-4pins@0 {
>>                                          reg = <0>;
>>                                          fsl,pinmux-ids = <
>
> That's right.

I'm getting into more cases like this: valid IOMUX configurations that my platform 
uses but are not included into imx28.dtsi.
So before adding new entries I was wondering whether it is a good idea to have IOMUX 
configurations in this include file at all. There are multiple valid combinations so 
why not adding these to the specific platform DTS files instead?

Existing IOMUX configurations in imx28.dtsi that later are not used by platform *.dts 
files are 'polluting' the final DTB with unused nodes.
Do other architectures follow the same approach?
Maybe there is a good reason that I simply don't see.

Hector

>
>> Example #2. My platform assembles a NAND chip which is powered at 1.8V.
>> The imx28.dtsi has a configuration 'gpmi_pins_a: gpmi-nand@0' that
>> configures the pins at 3.3V.
>> Should I create another entry here 'gpmi_pins_b: gpmi-nand@1' with
>> fsl,voltage = <0>; or should I create a specific entry in my platform's
>> DT instead?
>> What is the convention?
>
> Since it's the same pinset, I'd rather go for using gpmi_pins_a in your
> NAND chip node, but also overload the fsl,voltage property of
> gpmi_pins_a in your board device tree.
>
> That would give something like
>
> pinctrl@80018000 {
> 	gpmi_pins_a: gpmi-nand@0 {
> 		fsl,voltage = <0>;
> 	};
> };
>
> nand@deadbeef {
> 	pinctrl-names = "default";
> 	pinctrl-0 = <&gpmi_pins_a>;
> }
>
> But maybe Sascha will have a different view on this.
>
> Maxime
>