[i.MX Yocto Project LF6.1.1_1.0.0] Apply a PREEMPT_RT patch to "linux-imx_6.1" for i.MX6 Solo.

[daniel_lopez_p]

Hello, 

While working on a i.MX6 Solo based board, and using i.MX Yocto Project LF6.1.1_1.0.0 in order to develop a Linux i.MX 6.1.1 kernel image for our board, we've encountered some problems when trying to apply the "patch-6.1-rc7-rt5.patch" Real-Time patch (the one thought to fit better to Linux 6.1.1, because there's no specific RT patch for it ; as seen in https://cdn.kernel.org/pub/linux/kernel/projects/rt/6.1/older/) to the Linux kernel sources.

As stated in https://community.nxp.com/t5/i-MX-Processors/Sound-issue-on-linux-imx-6-1-1-with-imx8mn-evk/m-p/1643... by @emontmasson, the patch fails to work wile trying to patch "arch/arm/include/asm/thread_info.h" and "arch/arm/kernel/asm-offsets.c" files. It seems there could be a difference between Linux kernel's mainline version and "linux-imx".

In comparison to said post, the "Real Time Edge" tool (@JorgeCas's answer, in said post) doesn't seem to take into account i.MX6 boards, and it's neither what we're looking for... but we'd like to know THE REASON for said patch not to work for "linux-imx" 6.1.1 version, and HOW we could get "linux-imx" 6.1.1 to work as a Real-Time kernel. We've considered trying to apply the rejected modifications by ourselves, but that seems a very unreliable alternative.

Thank you, in advance!

Best regards,

Daniel.

[JorgeCas]

Hello,

As I mention on last post, those patches are not tested on our Kernel and hardware because Preemtive RT Linux is implemented on i.MX devices using Real Time Edge. emontmasson mentioned that he applied successfully the RT patch 6.1-rc7-rt5 and RT patch v6.1.26 with some adaptations compared to the mainline version, but there is no documentation to implement this and it is up to the customer to make the integration.

The list of supported devices for Real-Time Edge is:

= LS1046A.
- i.MX6ULL.
- LS1028A.
- i.MX8MMINI.
- LX2160A.
- LS1043A.
- IMX8MPLUS.
- LS1021A.
- LS1012A.
- i.MX8X.
- i.MX93.

Best regards.

Jorge.