Kernel Customization: Activate SD-Card and SPI0


I followed the Jetson Xavier NX Platform Adaptation and Bring-Up Guide for an own carrier board, but have still some problems.

I customized the pinmux spreadsheet from the Jetson Xavier NX and generated the dtsi files. With the dtsi files I generated a pinmux.cfg and a pad.cfg file. The most important changes in the kernel are the activations of the SD-Card on SDMMC3 and SPI0. I have done that for the Nano with no problems but I cannot find the necessary changes for the Xavier NX (production module). If my assumption is right there must be an entry in the DTSI where I change the SDMMC3 from “disabled” to “okay”. Same for SPI0 I guess.
Could someone please give me some hints how to do this? Any help much appreciated!

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If all you need to do is change the state you could just create an overlay that does it for those 2 devices and re-generate the dtb with it. That way you’re not changing and having to recompile the distributed dtb.

Thank you for your quick reply @gtj ! The basic problem is that I cannot find the related entries for SDMMC3 and SPI0. I would expect that these peripherals are defined somewhere and their state should be set to “disabled”. But where?

sdmmc3 is in the L4T/sources/hardware/nvidia/soc/t19x/kernel-dts/tegra194-soc/tegra194-soc-sdhci.dtsi.
spi0 is in tegra194-soc-spi.dtsi in that same directory. You’ll probably have to run “./” to get it, then rebuild the kernel.

Or you could decompile the running dtb, modify it, then re-compile it.

Or you could create a simple overlay that enables them. Something like this should work:

/ {
    overlay-name = "Custom";
    compatible = "nvidia,<use the correct part number here>";
    fragment@spi0 {
        target = < &spi0 >;
        __overlay__ {
            status = "okay";
    fragment@sdmmc3 {
        target = < &sdmmc3 >;
        __overlay__ {
            status = "okay";

Many thanks for your help! I did not follow the DTSI files and I missed the SOC file. In the end I made a copy of the board+SOC DTS file and added my modifications. Finally it worked!

BTW: The card detect pin CD for SDMMC3 is not on the same location where it used to be on the Nano. The only appearance I found in the Pinmux was a signal on the SOC which is not available on the card connector. For the moment I disabled the card detect mechanism, but the problem is that any card movement will not be recognized. Not a big issue since the card is not meant to be inserted at run time in my system but finally not nice. Any suggestion?

Yeah all I see is that CD for SDMMC3 is SOC_GPIO55. Nothing further.

thank you @gtj , I had enabled the SDMMC3 for SD card on my carrier board.