Public bug reported:
Impact:
While working on a bug that involved loading an overlay dtb files upon
boot, i noticed that, no matter what i put in config.txt::dtoverlay=...,
no overlay was loaded at all.
After further investigation i found that recently (~April 2017), the
raspberry BSP changed the overlay files suffix from -overlay.dtb to
.dtbo, and while the upstream bootloader was updated to accept the new
scheme, we keep shipping an older bootloader in the the archive that
didn't know about this change.
To make this bug more annoying, the bootloader doesn't emit an error or
a warning if it fails to load an overlay, it silently ignores it and
keep going.
Ubuntu core #stable isn't affected by this bug since it's shipping it's
own overlay files in a static tarball (using the old scheme), and #edge
(that is where new daily images are built) is shipping an older kernel
with the old scheme.
While #beta and #candidates should be affected.
Fix:
A way to fix this bug would be to update the raspi2 bootloader to a more
recent version, but since updating it has proven challenging in the past
(multiple images from multiple sources, #updates vs #security, different
boot configs, etc), i'm taking a more straightforward approach by
reverting the dtb overlay files rename back to the previous scheme.
With that said, i'm concurrently opening another LP bug (1703799)
because we must update the bootloader and revert this fix as soon as the
new bootloader lands in the archive.
How to test:
The are different ways you can test this (like modifying the
config.txt::dtoverlay=... parameter and then checking that the corresponding
hardware started to work, but then you would never know if it's a kernel driver
problem, a dtb merge problem, wrong wiring, failing hardware, etc), but the
best way is to use the dtc to dump out the dts structure before and after the
dtoverlay
modification and then diff the two:
vanilla image:
$ dtc -I fs -O dts /proc/device-tree > pi3-vanilla.dts
now install the new kernel with the revert (dpkg -i ... or snap install
...), modify dtoverlay, reboot and dump again:
# echo "dtoverlay=vc4-kms-v3d" >> /boot/firmware/config.txt
# reboot
$ dtc -I fs -O dts /proc/device-tree > pi3-vc4.dts
check if the dtb passed to the kernel has changed:
$ diff -du pi3-vanilla.dts pi3-vc4.dts
[check that there's actually a diff and something sensible was applied]
if you are doing this on ubuntu-core, config.txt is located in
/boot/uboot/config.txt, while if you are doing this in ubuntu classic,
remember to manually copy the overlay files that are shipped with the
new kernel:
# rm -rf /boot/firmware/overlays
# cp /lib/firmware/`uname -r`/device-tree/overlays /boot/firmware
--
** Affects: linux-raspi2 (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1703802
Title:
Overlay files don't get applied
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