linux-kernel - Re: Question of resource

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Message-ID: <1262132171.28789.136.camel@gandalf>
Date:	Wed, 30 Dec 2009 02:16:11 +0200
From:	Felipe Balbi <me@...ipebalbi.com>
To:	Joe Perches <joe@...ches.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Question of resource_size() implementation

On Tue, 2009-12-29 at 16:12 -0800, Joe Perches wrote:
> On Wed, 2009-12-30 at 01:43 +0200, Felipe Balbi wrote:
> > I'm wondering whether the +1 in resource_size() is actually necessary.
> > resource_size() is defined as:
> []
> > static inline resource_size_t resource_size(const struct resource *res)
> > {
> > 	return res->end - res->start + 1;
> > }
> > Are we off-by-one
> > here ? Or is this all expected ?
> 
> Imagine you have 1 byte sized resources.
> 
> AREA1 = 0x40000000
> AREA2 = 0x40000001
> 
> area1.start = 0x40000000
> area1.end   = 0x40000000
> 
> area2.start = 0x40000001
> area2.end   = 0x40000001

(adding lkml back to the loop)

in that you wouldn't use any of the SZ_* macros and simply hardcode
start and end, right ? then you would define:

area1.start = 0x40000000
area1.end = 0x40000001

and ioremap 2 bytes due to +1 in resource_size().

-- 
balbi

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