I have problem with passing flag from makefile to .c file.

During building external kernel module my macro isn't seen by compiler. I used plenty of ways.

First way:

ccflags-y += -DMY_FLAG

$(MAKE) -C $(KERNEL_SRC) M=$(SRC)

Second:

$(MAKE) -C $(KERNEL_SRC) M=$(SRC) CFLAGS_my-kernel-module.o="-DMY_FLAG"

Third:

$(MAKE) -C $(KERNEL_SRC) M=$(SRC) CFLAGS="-DMY_FLAG"  

Forth:

 $(MAKE) -C $(KERNEL_SRC) M=$(SRC) ccflags-y="-DMY_FLAG"   

In general I use bitbake to build external kernel modules.  And I wonder if bitbake doesn't introduce issue as some of above solution really should work. And additionally I had to use absolute paths in headers because relative didn't work so -I append also doesn't work:

SRC := $(shell pwd)

ccflags-y := -I$(SRC)

BR

Tomek