Accessing flash directly from User Space [SOLVED]

[Joakim Tjernlund]

Michael Buesch <mb at bu3sch.de> wrote on 31/10/2009 17:42:54:
>
> On Saturday 31 October 2009 14:26:48 Joakim Tjernlund wrote:
> > >
> > > > On Friday 30 October 2009 16:08:55 Alessandro Rubini wrote:
> > > > > > asm("eieio; sync");
> > > > >
> > > > > Hmm...
> > > > >    : : : "memory"
> > > > >
> > > > > And, doesn't ";" start a comment in assembly? (no, not on powerpc
> > > > it seems)
> > > >
> > > > Yes, I think the barrier is wrong.
> > > > Please try with
> > > >
> > > > #define mb()   __asm__ __volatile__("eieio\n sync\n" : : :
> > > > "memory")
> > >
> > > That definition worked great.  I must have missed the : : : "memory" bit when
> > > I was digging through code.
> > >
> > > Thanks, that gives me about a 2x speedup over the msync() calls.
> >
> > Exactly when should you use the barrier? At every access,
> > every read or when changing from write to read?
>
> Well, it depends on the device you are accessing. I'll give you a small pseudo example.
>
> mmio[0] = address;
> mmio[1] = data;
> mb();
> mmio[3] |= 0x01; /* This triggers an operation -> address=data */
> /* probably also need an mb() here, if the following code
>  * depends on the operation to be triggered. */

So anything that depends on the previous accesses needs a mb()
hmm, the mmio[0] and mmio[1] are written in order I hope?

 Jocke