Linux: Kernel 5.4.y and patch realtime

[antonellocaroli]

Applied patch-rt patch-5.4.40-rt24 regularly.
Compilation is successful on aarch64.

But at boot it hangs here:

does anyone have any solutions?

on rpi3, I didn't try on rpi4.

[schnitzeltony]

Smells like a port of [1-2] is required.

[1] https://github.com/schnitzeltony/meta-raspi-light/blob/master/recipes-kernel/linux/files/rt/0001-usb-dwc_otg-fix-system-lockup-when-interrupts-are-th.patch
[2] https://github.com/schnitzeltony/meta-raspi-light/blob/master/recipes-kernel/linux/files/rt/0002-usb-dwc_otg-fix-system-lockup-when-interrupts-are-th.patch

[antonellocaroli]

Thank you.

I tried, but it stops at the same place.

reboot and other errors.

[antonellocaroli]

did anyone happen to come up with any solutions?

I also tried with kernel 5.4.51 and patch-5.4.52-rt31.patch.xz

the boot always stops here:

[antonellocaroli]

to specify on raspberry3 aarch64 is not working.

on raspberry4 aarch64 it works instead.

[poerob]

Hello!
I'm also experiencing boot issues. I use an Raspberry Pi 4B 4Gb with 64 Bit Raspberry Pi OS. I patched the current branch with patch-5.4.54-rt32.patch.gz, patching and compiling worked without any problems. Now, the system freezes with a black screen after the "Raspberry Pi OS Welcome Screen" comes up. I also had a try with the 32Bit-Version, which came up with the same result. Are there any solutions or workarounds for this?

[pelwell]

I'm happy for you to use this issue to discuss problems with the realtime patches, and if you get to a stage where there is a combination of patches that work then I'll consider hosting them in an rpi-5.4.y-rt branch, just don't expect much support from the Pi devs.

[poerob]

I'm happy for you to use this issue to discuss problems with the realtime patches, and if you get to a stage where there is a combination of patches that work then I'll consider hosting them in an rpi-5.4.y-rt branch, just don't expect much support from the Pi devs.

Hi @pelwell, no problem, i'm just curious if somebody of the previous participants may have found a solution for this.

[poerob]

Some News: I tried a precompiled 64bit 5.4 kernel i found here, which was patched with 5.4.54-rt32.patch.gz. Now everything just works fine. Something in my toolchain seems to be faulty, so the problem is on my side.

[antonellocaroli]

@poerob interesting, on rpi3 or rpi4?

[poerob]

@poerob interesting, on rpi3 or rpi4?

Pi 4B 4GB

[antonellocaroli]

ok, on rpi4 my compilation had also worked...My problem is on rpi-3b

[poerob]

Did you follow all steps from the Documentation for Kernel Building ? Otherwise i can't help you, since i have no Modell 3B+ at my place. Sorry!

[antonellocaroli]

Just tried again with kernel 5.4.65 and patch-5.4.66-rt38.patch.gz

on aarch64.

Rpi4 no problem and it works (as I checked before)
Rpi3 same problem as above

[kdoren]

I built a Raspberry Pi realtime Kernel 5.4.81-rt45.
sources are here: https://github.com/kdoren/linux
also a pre-built 64-bit archive: https://github.com/kdoren/linux/releases

FYI the old 4.19 kernel doesn't work on newer Pi4's, USB is broken.

[antonellocaroli]

@kdoren

does it also work on Rpi3?

[kdoren]

I just tried it (64-bit rt kernel) on a Raspberry Pi 3B and it seems to work fine.

[antonellocaroli]

@kdoren
Sorry for the trivial question, but has the kernel been compiled with the Fully Preemptible Kernel (RT) option?
seeing the cpu usage, it seems not...

[kdoren]

@antonellocaroli
The config options are here: https://github.com/kdoren/linux/blob/rpi-5.4.81-rt/rt64.config
including:
CONFIG_PREEMPT_RT=y

[kdoren]

@antonellocaroli
You were correct, thanks for reporting.
Somehow I managed to build it with PREEMPT but not RT enabled.
I rebuilt it and posted a new file. This one is really PREEMPT_RT:

$ uname -a
Linux jambox 5.4.81-rt45-v8+ #9 SMP PREEMPT_RT Mon Dec 28 00:13:29 PST 2020 aarch64 GNU/Linux

The bad news is that now it doesn't boot on a Pi3, same problem you ran into.
To deal with that I'm putting a "[pi4]" filter in /boot/config.txt so that it only boots the 5.4 rt kernel on a Pi4.
Sorry about the false alarm.