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There is a hardware SPI device on my platform, but it doesn't appear in /dev. I read in internet that the hardware description is read during boor from device tree files (dtb).

The problem is that I did search in the filesystem and I was not able to find such a file.

Where does the bootloader search for *.dtb files at boot time?

I did log on start-up to see what the board does at boot-up. This is part of the log:

Normal Boot
    Hit any key to stop autoboot:  1  0 
    switch to partitions #0, OK
    mmc1(part 0) is current device
    switch to partitions #0, OK
    mmc1(part 0) is current device
    reading /uEnv.txt
    ** Unable to read file /uEnv.txt **
    reading /boot.scr
    ** Unable to read file /boot.scr **
    reading /zImage
    6116584 bytes read in 159 ms (36.7 MiB/s)
    Booting from mmc ...
    fdt_file=imx6ul-var-dart-emmc_wifi.dtb
    reading /imx6ul-var-dart-emmc_wifi.dtb
    30601 bytes read in 21 ms (1.4 MiB/s)
    Kernel image @ 0x82000000 [ 0x000000 - 0x5d54e8 ]
    ## Flattened Device Tree blob at 83000000
       Booting using the fdt blob at 0x83000000
       Using Device Tree in place at 83000000, end 8300a788

    Starting kernel ...

And this is the entire log.

My goal is to avoid rebuilding the entire kernel. Instead rebuild just the device tree for files for current platform.

  • The device tree blob is in the zImage. zImage is a compressed linux kernel and dtb. Not always, you should be able to pass switches to the boot loader to read your modified dtb from another location other than zImage. – jc__ Aug 22 '18 at 13:12
  • May be able to pass switches to the kernel also to read a different dtb... – jc__ Aug 22 '18 at 13:14

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