DISABLE MMU for freescale i.MX28

Hi everyone, recently I got a freescale i.MX28 and decided to use JTAG to make a fault injection in program memory, however with MMU and D-cache enable, program wouldn't write data into phy mem directly,so I really want to disable it.
What am I done to disable it is to change build_dir/target-arm_arm926ej-s_musl_eabi/linux-mxs/linux-4.14.104/arch/arm/include/asm/cp15.h with
#define CR_M (0 << 1)
#define CR_C (0 << 2)
#define CR_S (0 << 8)
#define CR_R (0 << 9)
#define CR_I (0 << 12)

and use make V=s successfully re-compile it.
But that doesn't work at all, I'm wondering whether need to use "make clean && make" to clean whole pre-compile files or change something else in the source code.
Anyone who have ever tried it can help me?
Thanks!