Comment 0 for bug 1782121

Impact:

Overlay dtb files should be applied to the main board dtb, before it's being passed down to the kernel for boot - but this didn't happen in the arm64 variant of the bionic/raspi2 kernel.

/boot/firmware/config.txt:
...
dtoverlay=pitft35-resistive

/boot/firmware/cmdline.txt:
dwc_otg.lpm_enable=0 console=serial0,115200 console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline rootwait fbcon=map:10 fbcon=font:VGA8x8

But the attached second display is never initialized.

Fix:

The main dtb must be built with symbols, to let overlay files find which section to patch - the applied patch does exactly that.

Apply, build, install and reboot:

dmesg:
...
[ 5.144664] fbtft: module is from the staging directory, the quality is unknown, you have been warned.
[ 5.145814] fbtft: module verification failed: signature and/or required key missing - tainting kernel
[ 5.157547] fb_hx8357d: module is from the staging directory, the quality is unknown, you have been warned.
[ 5.158349] fbtft_of_value: buswidth = 8
[ 5.158362] fbtft_of_value: debug = 0
[ 5.158366] fbtft_of_value: rotate = 90
[ 5.158372] fbtft_of_value: fps = 25

ubuntu@raspi64:~$ ls -la /dev/fb1
crw-rw---- 1 root video 29, 1 Jan 28 15:58 /dev/fb1

Regression risk:

We only change how the arm64 raspi2 dtbs are generated, and since we didn't produce any image using this kernel so far, the regression risk is zero.

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