RT patch for linux-mainline 5.14.0

Hello, I am trying to make an RT kernel for VIM3. I find that the RT kernel is not available from the official image, so I decided to make an RT version by myself based on the build procedure from the link Build Ubuntu/Debian Images | Khadas Documentation. The patch is from the link https://cdn.kernel.org/pub/linux/kernel/projects/rt/5.14/older/patch-5.14-rt17.patch.xz . The patch processing is ok and without any mistake or warning. However, when ‘make linux-config’, I can’t find the 'Fully Preempt ’ option in the ‘general setup ’ Preempt mode’(but for ‘make menuconfig ARCH=arm’ and ‘make menuconfig ARCH=x86’ things are just right). There are two questions: the first is that I saw some patch from Khadas besides the mainline kernel, what are they patching for? The second question is will there be official support for a RT patched kernel or some guide about that?

Please check whether some dependent configurations are missing.

‘Fully Preempt’ option depends on ARCH_SUPPORTS_RT and EXPERT, for the last one, I have set that in the configuration file. But for the first one, ’ select ARCH_SUPPORTS_RT if HAVE_POSIX_CPU_TIMERS_TASK_WORK’, so it depends on HAVE_POSIX_CPU_TIMERS_TASK_WORK, and HAVE_POSIX_CPU_TIMERS_TASK_WORK depends on KVM. This part confused me a lot since in ./arch/arm/Kconfig, all things about HAVE_POSIX_CPU_TIMERS_TASK_WORK is the same. I can work around this, just don’t know what really happened behind.