linux-kernel - Re: recent IDE regression

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Message-ID: <20080725084607.GQ26938@trinity.fluff.org>
Date:	Fri, 25 Jul 2008 09:46:07 +0100
From:	Ben Dooks <ben-linux@...ff.org>
To:	David Miller <davem@...emloft.net>
Cc:	ben-linux@...ff.org, bzolnier@...il.com, harvey.harrison@...il.com,
	linux-ide@...nel.org, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org
Subject: Re: recent IDE regression

On Fri, Jul 25, 2008 at 01:42:52AM -0700, David Miller wrote:
> From: Ben Dooks <ben-linux@...ff.org>
> Date: Fri, 25 Jul 2008 09:34:48 +0100
> 
> > On Thu, Jul 24, 2008 at 11:38:31PM -0700, David Miller wrote:
> > > diff --git a/drivers/ide/ide-iops.c b/drivers/ide/ide-iops.c
> > > index 07da5fb..8aae917 100644
> > > --- a/drivers/ide/ide-iops.c
> > > +++ b/drivers/ide/ide-iops.c
> > > @@ -510,10 +510,8 @@ void ide_fixstring (u8 *s, const int bytecount, const int byteswap)
> > >  
> > >  	if (byteswap) {
> > >  		/* convert from big-endian to host byte order */
> > > -		for (p = end ; p != s;) {
> > > -			unsigned short *pp = (unsigned short *) (p -= 2);
> > > -			*pp = ntohs(*pp);
> > > -		}
> > > +		for (p = end ; p != s;)
> > > +			be16_to_cpus((u16 *)(p -= 2));
> > 
> > personally, i would much prefer to see the loop being less evil
> > like:
> > 
> > 	for (p = s; p < end; p += 2)
> > 		be16_to_cpus((u16 *)p);
> > 
> > is there an architecture/compiler combo which really makes this
> > evil worthwile? on arm (gcc 4.2), both evaluate to the same number of
> > instructions.
> 
> Regardless of what we want to do with this ugly loop, the endianness
> macros should be fixed to consistently evaluate their arguments
> once just like real function calls do.

Yes, I wasn't saying the macro fixes are not worthwile. I would also
like to see the loop being fixed to not perpetrate this nasty code
any further.

-- 
Ben

Q:      What's a light-year?
A:      One-third less calories than a regular year.

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