linux-kernel - Re: [PATCH v2 2/3] ARM: Use include/asm-generic/io.h

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Message-Id: <201407121427.22668.arnd@arndb.de>
Date:	Sat, 12 Jul 2014 14:27:22 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	Thierry Reding <thierry.reding@...il.com>,
	Russell King <linux@....linux.org.uk>,
	Will Deacon <Will.Deacon@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/3] ARM: Use include/asm-generic/io.h

On Friday 11 July 2014, Catalin Marinas wrote:
> 
> On Fri, Jul 11, 2014 at 04:31:11PM +0100, Thierry Reding wrote:
> > diff --git a/arch/arm/include/asm/io.h b/arch/arm/include/asm/io.h
> > index a78562f21aab..ef54f5c8a7ae 100644
> > --- a/arch/arm/include/asm/io.h
> > +++ b/arch/arm/include/asm/io.h
> [...]
> > -#define iowrite16be(v,p) ({ __iowmb(); __raw_writew((__force __u16)cpu_to_be16(v), p); })
> > -#define iowrite32be(v,p) ({ __iowmb(); __raw_writel((__force __u32)cpu_to_be32(v), p); })
> 
> Aren't you losing the barrier semantics here? The generic iowrite*be()
> functions call __raw_write*() directly which don't have a barrier
> (write* accessors do).
> 

Indeed, sorry for missing this. The generic implementation still makes sense for
include/asm-generic, but arm32 and arm64 must provide their own versions here.

An alternative would be to define

#define iowrite32be(v, p) iowrite32(swab32(v), p)

which is correct but can end up swapping multiple twice.

	Arnd
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