linux-kernel - Re: [PATCH 5/7] Alter get_order() so that it can make use of ilog2() on a constant [try #3]

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Date:	Tue, 19 Sep 2006 08:03:24 -0700
From:	Andrew Morton <akpm@...l.org>
To:	David Howells <dhowells@...hat.com>
Cc:	torvalds@...l.org, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH 5/7] Alter get_order() so that it can make use of
 ilog2() on a constant [try #3]

On Tue, 19 Sep 2006 10:08:17 +0100
David Howells <dhowells@...hat.com> wrote:

> > I didn't pursue it further, because sprinkling ARCH_HAS_FOO things into
> > bitops.h(!) is all rather hacky.  Better to use CONFIG_* so they're always
> > visible and one knows where to go to find things.
> 
> But (1) they're not config options,

Well they are, really.  "This architecture has its own get_order()".  It's
not *user* configurable, but neither is, say CONFIG_GENERIC_HARDIRQS.

The problem we have with the ARCH_HAS_FOO things is that there's never been
an include/asm/arch_has_foo.h in which to define them, so stuff gets
sprinkled all over the place.

> and (2) there's plenty of precedent for
> this sort of thing (ARCH_HAS_PREFETCH for example).

There's precedent both ways.  The advantages of doing it in config are

a) You know where to go to find it: arch/foo/Kconfig

b) It's always available, due to forced inclusion of config.h.

(I think I actually would prefer include/asm/arch_has_foo.h if we had it,
because it's lighter-weight.  But we don't)
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