Verdin pin MUX overlay

Technical Support
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1

Hi,

I am working on a device tree overlay for a Verdin iMX8m Mini. One thing required with this is to customize the pin MUX. It is working OK but there is something I do not understand and would like clarified.

Following your document on this (here), I have applied the following overlay:

/* Databerry S36051 Device Tree Overlay
 * Device tree customisation:
 *  - Swap Pin 15 from the default assigned PWM channel to the required GPIO
*/

/dts-v1/;
/plugin/;

/*#include <device-trees/dts-arm64/imx8mm-pinfunc.h>*/
#include "imx8mm-pinfunc.h"

/ {
	compatible = "toradex,verdin-imx8mm";
};

&pwm2 {
	status = "disabled";
};

&iomuxc {

  /* Re-definition of the "default" pinctrl names. This is originally defined in the imx8mm-verdin.dtsi file in the $iomuxc node. It
   * is redefined here by keeping the original set of pin control phandles, but then adding the new one which is defined below.
  */
  pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_gpio1>, <&pinctrl_gpio2>,
		    <&pinctrl_gpio3>, <&pinctrl_gpio4>,
		    <&pinctrl_gpio7>, <&pinctrl_gpio8>,
		    <&pinctrl_gpio_hog1>, <&pinctrl_gpio_hog2>, <&pinctrl_gpio_hog3>,
		    <&pinctrl_pmic_tpm_ena>,
        <&pinctrl_s36051_gpios>;

  verdin-imx8mm {

    /* New pin control group for the S36051 device tree */
    pinctrl_s36051_gpios: s36051_gpio_grp {
      fsl,pins = <
        MX8MM_IOMUXC_SPDIF_RX_GPIO5_IO4 0x106 /* SODIMM 15 -> ALT5 gpio5.IO[4], with Drive Strength = X6, pull-down resistor enabled */
                
        /* Other similar lines could be placed here for other pins */

      >;

    };

  };

};

In your document there is the following note:

*Depending on the SoM you might have to put the pin control node inside another node named after the SoM, like apalis-imx8qm. Check the iomuxc declaration in the Device Tree and use it as reference.

I went and looked at the iomuxc declaration (in imx8mm.dtsi) but could not see anything there that guided me as to whether this was necessary or not, nor what the node should be called (assuming it was necessary).

You will see on line 33 that I have put the pin control node inside a node called “verdin-imx8mm”. This works. However, it also works if I do not put it inside such a node. My guess is that in the case of this SoM, this is not necessary. Please would you clarify this, and if it is required, what should the name be?

Also, what is the meaning of the “grp” suffix used on many on the nodes – does it mean “group”?

Thanks for your help,

Peter

2

Hi @bcpberry ,

Yes, as far as I know the grp suffix means group, as it is used in pin control nodes.

I looked at the article and the note you quoted is indeed not very clear. What you should do is check how pin control nodes are declared in the unaltered device tree:

  • If pin control nodes are declared directly inside iomuxc, new ones should be declared likewise, as seen in the Verdin iMX8M Mini device tree (imx8mm-verdin.dtsi, line 820);
  • If pin control nodes are declared inside a node named after the SoM, new ones should also follow that, as it is the case with Apalis iMX8 (imx8qm-apalis.dtsi, line 306).

In summary, when declaring new pin control nodes you put them like you see the previous ones.

I will ask the team to rewrite the note so that becomes clear. Thank you for your feedback!

Hope this explains things for you.

Best regards,
Lucas Akira

3

Thanks @lucas_a.tx - great answer.

Peter