Bad volatile -mstrict-align code on powerpc on 4.0.2?

[Peter Dufault]

On Nov 6, 2005, at 4:43 PM, Till Straumann wrote:

> IMO it is better coding practice to use in_be16/out_be16 (or
> ld_be16/st_be16 if you are sure you don't need the eieio)
> for memory-mapped device register access.

It turns out I do need eieio.  Which is too bad for my legacy code.   
I have something like this:

volatile struct st_reg {
    int muxsel;
    int value; } *reg = (volatile struct st_reg *)0xa000;

int mv = reg->muxsel;
reg->muxsel = mv|0x01;
int value = reg->value;

and the read of value is happening before the write of muxsel without  
the eieio.  With the eieio it works properly (verified on a bus  
analyzer).

The compiler shouldn't reorder those since the struct is volatile.   
Is there a setting for the VME bus interface to prevent this?  I'd  
expect a read through the same bus mapping to block until all writes  
flushed.

Again, this is to help support legacy code, not to discuss how to do  
it properly.

Peter