is there dummy r/w in mips kernel API

[loody <miloody@gmail.com>]

Dear all:
I am trying porting usb on mips platform.
Due to hw limitation, I have to do the dummy read to make sure data
has been written to the memory, so I announce an volatile parameter,
tmp, such that cpu will read the same address back to me.

Below is what I try to do in usb driver:
                        wmb ();
    389c:       0000000f        sync
                        dummy->hw_token = token;
    38a0:       ae740008        sw      s4,8(s3)
                        tmp = dummy->hw_token;
    38a4:       afb40010        sw      s4,16(sp)
as you can see, the compiler is so smart that he read the register
content instead of re-read the memory for accelerating the read speed.
unfortunately, that isn't I want. Is there already exist kernel API can help me?
appreciate your help,
miloody