cr9c1
Posts: 10
Joined: Wed Apr 15, 2015 11:52 pm

Newer Kernels and dtoverlays

Wed Mar 28, 2018 2:09 pm

So I've compiled some of the newer kernels that I cloned from the raspberrypi github page, 4.15.13, and 4.15.10, and I believe I even tried 4.16.x, I can't remember. I use the bcmrpi3_defconfig and everything usually goes pretty well. I have noticed however, that things like disabling wifi via overlay (dtoverlay=pi3-disable-wifi) doesn't work with any of the 4.15 or 4.16 kernels. I made sure to copy over the freshly compiled dtbs and dtbos into my boot and boot/overlays so everything was updated per the compiled kernel version but no dice.

If I go back to the 4.9.y branch, everything works. I'm just curious if maybe there is some work the rpi foundation does on the newer kernels to enable the overlay functions to work which is why I can't get them to work? Obviously there are other ways to disable the wifi/and/or bluetooth but I usually use the overlay option. I just wanted to be sure I wasn't missing something in my kernel configuration or doing something "wrong". I typically use the kernel released through the apt repo, but have recently started building newer kernels (mostly for my pi 3 b+) and playing around with aarch64 operating systems and kernels.

Any insight would be appreciated. I'm kind of at a loss as to why the dtbo overlays will not load on the newer kernels but function perfectly on the 4.9.y branch.

PhilE
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 2536
Joined: Mon Sep 29, 2014 1:07 pm
Location: Cambridge

Re: Newer Kernels and dtoverlays

Wed Mar 28, 2018 2:37 pm

We don't support the 64-bit builds so the two worlds can drift apart, but there shouldn't be any fundamental reason why overlays don't work.

"sudo vcdbg log msg" will show you progress and error messages from the firmware, including DT-related issues. You can get more information by adding "dtdebug=1" to config.txt. However, you may find it quicker and easier to use the "dtmerge" and "dtdiff" command line utilities to apply overlays to a base DTB and see what changes.

cr9c1
Posts: 10
Joined: Wed Apr 15, 2015 11:52 pm

Re: Newer Kernels and dtoverlays

Wed Mar 28, 2018 2:42 pm

Thanks. I just thought it strange that when I build 4.9.y as aarch64, it works perfect, but the 4.15 and 4.16 builds just do not appear to load the overlay. I've been testing solely on the pi3-disable-wireless dtbo, which obviously works perfect under the armhf raspbian build on the pi3 b+, and works fine under 4.9.y build 64 bit, but not the others. Short of what you have already recommended, are there any other ways to trouble shoot why the dtbo isn't being loaded or processed by the system?

PhilE
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 2536
Joined: Mon Sep 29, 2014 1:07 pm
Location: Cambridge

Re: Newer Kernels and dtoverlays

Wed Mar 28, 2018 2:44 pm

No - you either need visibility of what the firmware is doing ("sudo vcdbg log msg") or a standalone tool that does the same thing ("dtmerge").

cr9c1
Posts: 10
Joined: Wed Apr 15, 2015 11:52 pm

Re: Newer Kernels and dtoverlays

Wed Mar 28, 2018 4:02 pm

Thank you. I will see what I can come up with.

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