If I'm not wrong ,your question is how to change the kernel version in OpenWRT.
Let's say I'm using
OpenWRT: CC 15.05 Target system: Atheros AR7xxx/AR9xxx
The current version of kernel is 3.18 and I want to downgrade to 3.17
There are 2 folders you need to care :
Step1.Edit the Makefile in openwrt/target/linux/ar71xx/Makefile
- KERNEL_PATCHVER:=3.18 + KERNEL_PATCHVER:=3.17
Step2.Create the configuration files for your kernel
I suggest you just copy the config-3.18 to config-3.17. You can modify them later by
cd openwrt make kernel_menuconfig
Step3.Try to compile it:
cd openwrt make target/linux/clean make target/linux/compile V=s
For the first time,the kernel source code linux-3.17.tar.xz will be downloaded into openwrt/dl. Then it's uncompressed and compiled without any patches.
Step4. Create folder patches-3.17 then put your own kernel patches (from Candela Tech) in it.
Repeat with Step3.
To make a patch file in OpenWRT ,you can take a look on this link https://wiki.openwrt.org/doc/devel/patches