[U-Boot] [PATCH] mpc83xx: Make it boot again

[Wood Scott-B07421]

Timur Tabi wrote:
> Wood Scott-B07421 wrote:
> > To be totally safe, we probably want to do a readback plus twi (to turn
> > a data dependency into a flow dependency) before the isync.
> 
> twi == trap word immediate?

Yes.

> If so, I don't see how that will turn a data dependency into a flow dependency.
> Is that some sort of side effect of twi?

It decides based on the input register (data dependency) whether to cause a trap (flow dependency).  We never want it to actually trap, so we set a condition that says never trap, but the dependency is still there -- the hardware doesn't decode it as a no-op.

See arch/powerpc/include/asm/io.h, it's used in the I/O read accessors.

-Scott