[vikky@server iuso]$ find .
.
./Makefile
./A
./A/Makefile
./A/file.c
[vikky@server iuso]$ cat Makefile 

run_sub_makefile:
        cd A && make

.PHONE: run_sub_makefile
[vikky@server iuso]$ cat A/Makefile 
#stupid rule just for example
file:file.c
        cp file.c file
clean:
        rm file