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Date: Wed, 7 Sep 2005 21:51:35 -0300
From: Marcelo Tosatti <marcelo.tosatti@cyclades.com>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
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Cc: Paul Mackerras <paulus@samba.org>,
	linux-ppc-embedded <linuxppc-embedded@ozlabs.org>
Subject: Re: [PATCH] add big endian version of ld_/st_ IO access macros and
	convert main 8xx code to use it
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On Thu, Sep 08, 2005 at 10:28:52AM +1000, Benjamin Herrenschmidt wrote:
> On Wed, 2005-09-07 at 20:03 -0300, Marcelo Tosatti wrote:
> > Hi,
> > 
> > The following patch adds big endian version of ld_/st_ macros 
> > and converts core 8xx code to use them.
> > 
> > Other than making IO accesses explicit (which is a plus for
> > readability), a common set of macros provides a unified place for the
> > volatile flag to constraint compiler code reordering.
> > 
> > There are several unlucky places at the moment which lack the 
> > volatile flag.
> 
> I'm not fan of the approach. You should use in_/out_ macros for IOs. If
> you don't need eieio on 8xx , then just #ifdef it out of the
> implementation of these.

The reason for that is that in_/out_ are supposed to be the standard 
IO macros (conformance)? In practice most drivers using the std macros
can benefit from the change. 

A common routine is shared by all architectures. Doing something like

/*
 * 8, 16 and 32 bit, big and little endian I/O operations, with barrier.
 */
extern inline int in_8(volatile unsigned char __iomem *addr)
{
        int ret;

        __asm__ __volatile__(
                "lbz%U1%X1 %0,%1;\n"
#ifndef CONFIG_8xx
                "twi 0,%0,0;\n"
                "isync" : "=r" (ret) : "m" (*addr));
#else
                : "=r" (ret) : "m" (*addr));
#endif
        return ret;
}

Seems somewhat ugly?