Apply Linux rt-patch to Petalinux

petalinux-rt-patch.txt

1. Find your kernel version according to the kernel Makefile. Example:
  # SPDX-License-Identifier: GPL-2.0
  VERSION = 6
  PATCHLEVEL = 1
  SUBLEVEL = 0
  EXTRAVERSION =
  NAME = Hurr durr I'ma ninja sloth

2. Clone the correct tag from github into <plnx-proj-root>/components/linux-xlnx-rt/:
    git clone https://github.com/Xilinx/linux-xlnx.git

3. According to your kernel version download the equivalent rt-patch version from:
    https://mirrors.edge.kernel.org/pub/linux/kernel/projects/rt/

4. Copy the *-patch.gz file to <plnx-proj-root>/components/linux-xlnx-rt folder.
5. cd linux-xlnx-rt
6. Patch the kernel sources by running: zcat ../*.patch.gz | patch -p1
7. Run petalinux-config and set: 
            linux Components Selection -> linux-kernel and change option from linux-xlnx to ext-local-src
            linux Components Selection-> External linux-kernel local source settings-> <plnx-proj-root>/components/linux-xlnx-rt
8. Save and exit configuration.
9. Run petalinux-config -c kernel and set:
     General setup -> Timers subsystem "High Resolution Timer Support"
     General Setup menu and to--> Preemption Model
                  Select "Fully Preemptive Kernel (RT)"
     Kernel Features -> select Timer frequency and set it to 1000 Hz
     CPU power Management -> Disable the CPU frequency scaling
10. Save configuration and exit.
11. Clean project: petalinux-build -x mrproper
12. Build just the kernel with no errors:
    petalinux-build -c kernel
13. Build all: petalinux-build
14. Following boot, <uname -a> command should output SMP PREEMPT_RT in kernel title.
            
<Based on https://www.hackster.io/LogicTronix/real-time-optimization-in-petalinux-with-rt-patch-on-mpsoc-5f4832>