volatile with O2

[thomas joseph <thomascanny at yahoo dot co dot nz>]

Hi All,
 I have a small problem with volatile and O2.
  I try to access device registers which are memory
  mapped in to user space. When I try to read the
  registers the application shows  different values 
  from those of driver. 

  I defined all the necessary members as volatile. But

  still it does not help. But when I inserted a 
  memory barrier before accessing those registers
  I seem to be getting the correct values.

The code looks like this.
 #define mb() __asm__ __volatile__ ("lock; addl $0,
0%%esp): : :"memory")


    mb();

    /* ulStatus is volatile unsigned long. */
    regStatus = pIpRegs->ulStatus;

    mb();

    Basically I am not sure why I need to use mb()
    in user space or Is it necessary for this kind of
    an application ?

    Or is the driver I am using is faulty. Actuall the
    driver uses remap_page_range with page protection 
    flags set as __PAG_PCD | __PAGE_PWT, which 
    disables caching for the mapped area.

 Could some body help me with this problem or if I
need to use any other compiler option pls inform me.
I tried -fvolatile as well. But it does not help.


 Thanks and Regards,
 --thomas

 



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