如何调试linux dp83640 驱动？how to debug dp83640.c ？ Why ”printk“ does not print any infomation on screen or by dmesg command？

we are using dp83640 connected whit arm3357. linux 3.2 run on the board. I edit the /net/phy/dp83640.c by adding printk in each function. but after I use testptp.c 

in \Documentation\ptp\ and run it.  the ptp devices can be found and I can run testptp. But there is no  output information in dp83640.c.

the printk consol level has been edit to 7 so the screen can capture any  information of printk.

这个问题要请 MCU 版块的大侠来解答

OK ,thanks