Wi-Fi Interface disappeared after sudden reboot

[LorenzoAncora]

Problem

After entering the DTB files in the firmware directory, everything was fine and the wireless interfaces worked perfectly. Yesterday evening the electric power went out for ~2 hours and, when the board restarted, wlan0 disappeared. After several reboots the situation is unchanged, even though the driver brcmfmac is in memory and is in use.

Details

• The Ethernet and local interfaces are fully functional, the problem concerns only the wireless interfaces;
• Apparently the kernel ring buffer does not contain any information useful for diagnosing the problem;
• /boot/firmware contains only two DTB files, the firmware configuration for boot and some kernel binaries.

^{Related to: #37}

[LorenzoAncora]

Cause

The Raspberry Pi 3 B was loading the bcm2837 DTB instead of the correct device tree.

Solution

I've discovered that after removing it the device would not boot (stuck on the rainbow test screen) and I've edited config.txt with an SD card reader, discovering that a script replaced the name of the correct device tree with device_tree=bcm2837-rpi-3-b.dtb.
Replacing device_tree=bcm2837-rpi-3-b.dtb with device_tree=bcm2710-rpi-3-b.dtb in config.txt and replacing bcm2710-rpi-3-b.dtb with a previous version of itself solved the problem.

Conclusion

• Always backup the old working DTB.
• After each system update with the experimental architecture you have to check config.txt. PITA.

[jlu5]

If you're using custom .dtb's, it may help to purge the raspi3-firmware package so that it can't overwrite things (I stumbled into this problem setting up my RPi too)

[LorenzoAncora]

@jlu5 TY for you suggestion.

If you're using custom .dtb's

No, I am only using older versions of the official ones. Without doing that the kernel does not recognize the wireless interface and I cannot use Internet.

purge the raspi3-firmware package so that it can't overwrite things

This package contains all the proprietary files necessary to boot a Raspberry Pi^® 3 board.
Purging this package will remove those (proprietary) files:

/etc/kernel/postinst.d/raspi3-firmware
/usr/lib/raspi3-firmware/bootcode.bin
/usr/lib/raspi3-firmware/fixup.dat
/usr/lib/raspi3-firmware/fixup_cd.dat
/usr/lib/raspi3-firmware/fixup_db.dat
/usr/lib/raspi3-firmware/fixup_x.dat
/usr/lib/raspi3-firmware/start.elf
/usr/lib/raspi3-firmware/start_cd.elf
/usr/lib/raspi3-firmware/start_db.elf
/usr/lib/raspi3-firmware/start_x.elf

On paper it's not a bad idea but what are the secondary effects?