Re: [meta-raspberrypi] Is Preempt-rt still supported in master / latest releases?

["Carles Sole" <Carles.SoleMendi@de.bosch.com>]

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Hi Alex, Andrei,

thanks for your reply. Based on your feedback I've tried the following:
- I have downloaded the patch patch-5.15.86-rt56.patch from https://cdn.kernel.org/pub/linux/kernel/projects/rt/5.15/ and stored in ./meta-raspberrypi/recipes-kernel/linux/files
- I have created a file linux-raspberrypi_%.bbappend in ./meta-raspberrypi/recipes-kernel/linux
- I have created a .cfg file with CONFIG_PREEMPT_RT_FULL = y in ./meta-raspberrypi/recipes-kernel/linux/files
- I have added both patch and cfg file in bbappend using SRC_URI:append:rpi.

I can observe the following:
- patch and cfg files are available in ./build/tmp/work/raspberrypi4_64-agl-linux/linux-raspberrypi/1_5.15.34+gitAUTOINC+e1b976ee4f_0086da6acd-r0
- new folder linux-raspberrypi4_64-preempt-rt-build is available inside the folder above. But the problem seems to be that CONFIG_PREEMPT_RT = y is not applied to the .config file. So it seems the preempt-rt kernel is built but without the full preempt-rt support.
- When I do bitbake linux-raspberrypi -c menuconfig I cannot select the full real time preempt kernel, only preemptible option available is --> Preemptible Kernel (Low-Latency Desktop). Fully Preemptible Kernel (Real-Time) is not available.
- When I flash the image in the Rpi4 and run uname -r I see that the rt kernel has been built --> 5.15.34.rt56.v8
- but only with PREEMPT option but without RT when I do uname -v --> #1 SMP PREEMPT Tue Aug 9 21:20:00 UTC 2022 (without RT).

I have tried building linux-yocto-rt for qemu and there I see that CONFIG_PREEMP_RT = y is available in the .config file. Also if I open menuconfig I have the option to select in General setup --> Preemption Model --> Fully Preemptible Kernel (Real-Time)

If you can provide any hints on what am I missing it would be highly appreciated.

Best Regards,
Carles

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