[Scarthgap] Kernel Version

[Allegra42]

From a LTS perspective, it's absolutely right to keep on the 6.6.x kernel, but unfortunately, the rpi-6.6.y branch of the Raspberry Pi's Linux kernel repo did not pulled in any updates in 8 months (https://github.com/raspberrypi/linux/tree/rpi-6.6.y).
Switching to 6.12.x would may result in compatibility issues.
I do not have a good and easy solution for this problem, but I want to point on the situation because I think this fact is not clear and open the discussion.

[kraj]

Switching kernel version to 6.12 on scarthgap would need some additional work. e.g. do we need to also bump version of linux-libc-headers. if not then how does test results pan out with 6.12 using existing scarthgap kernel headers.

[Allegra42]

@kraj did you ever evaluate linux-yocto instead of the Raspberry Pi Kernel? While I fully understand the concerns about switching to 6.12, I also do not consider staying with an unmaintained kernel branch as a good option.

[the-gabe]

did you ever evaluate linux-yocto instead of the Raspberry Pi Kernel?

@Allegra42 I tried exactly this a few days ago, and my key issue was getting it to play nicely with u-boot, I think with some changes to device trees I think it will work. But this will only be possible for 4th gen Pi devices, the CM5 iirc is not yet fully upstream (might be wrong now).

For now, I'm using 6.12 and I have a bbappend that looks like:

# Override kernel version and SRCREVs for 6.12
LINUX_VERSION = "6.12.60"
SRCREV_machine = "9b20e2bfe5ded1605bf9f3eb205156f5911843db"
SRCREV_meta = "0b45d854fcd717571edc261515273c17bfe57ad3"
LINUX_RPI_BRANCH = "rpi-6.12.y"
LINUX_RPI_KMETA_BRANCH = "yocto-6.12"

and we then set

PREFERRED_VERSION_linux-raspberrypi:forcevariable = "6.12.%"

in our distro configuration.

[rob3c]

I've been dealing with similar issues on Raspberry Pi 5, since the Hailo 8/8L kernel drivers and libraries are sensitive to specific kernel point releases to work without major problems.

I've already created a linux-raspberrypi_6.12.bbappend similar to the above that uses 6.12.47, which matches the latest Pi OS for its bookworm and trixie debian-based releases.

However, it also looks like I need to at least create linux-firmware-rpidistro_%.bbapppend that also bumps the upstream RPi-Distro/firmware-nonfree variables SRCREV (commit) and PV (release tag) to values matching their bump to the same kernel. And who knows what else should really be updated while I'm at it? For example, do I need to override a SRCREV anywhere for the raspberrypi/firmware commit for 6.12.47?

The general patching process for Yocto is pretty well documented, but I'm wondering about meta-raspberrypi specifically. Is the process documented anywhere besides the source itself and the git history for guidance on upgrading/backporting this project's dependencies for staying on a Yocto LTS release like scarthgap while keeping up with bug fixes and such? So far, the commits haven't been very consistent in what gets updated from what I've seen when trying to sort through this, and there isn't usually much elaboration on why specific changes were or weren't made.

[Allegra42]

I'd hope for a good documentation on the general issue, possible ways to deal with and gain some awareness for the basic issue behind. The Raspberry Pi foundation is aware their devices are used in commercial and industrial use-cases but leave critical aspects like long-term maintenance of the kernel and Yocto in general behind and maintained by the community on a "best effort" base (and it's the same for the RP microcontrollers and e.g. Zephyr), and depending on a manufacturer who does not care about the long-term aspects is just a risk with upcoming regulations like CRA.
I do not expect a real solution for this issue here, as it is complex and would probably need participation from the Foundation.

That's also the reason for opening this issue and asking about your all experiences with mainline kernels (having the linux-yocto in mind), which is as well tricky with closed source firmware components