linux-kernel - Re: [PATCH] isdn: hisax: netjet requires VIRT_TO

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Message-Id: <201303151015.00746.arnd@arndb.de>
Date:	Fri, 15 Mar 2013 10:15:00 +0000
From:	Arnd Bergmann <arnd@...db.de>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Karsten Keil <isdn@...ux-pingi.de>, netdev@...r.kernel.org,
	David Howells <dhowells@...hat.com>
Subject: Re: [PATCH] isdn: hisax: netjet requires VIRT_TO_BUS

On Friday 15 March 2013, Geert Uytterhoeven wrote:
> On Thu, Mar 14, 2013 at 10:56 PM, Arnd Bergmann <arnd@...db.de> wrote:
> > Disabling CONFIG_VIRT_TO_BUS on ARM showed that the hisax netjet
> > driver depends on this deprecated functionality but is not
> > marked so in Kconfig.
> >
> > Rather than adding ARM to the already long list of architectures
> > that this driver is broken on, this patch adds 'depends on
> > VIRT_TO_BUS' and removes the dependency on !SPARC, which is
> > also implied by that.
> 
> IIRC, the real "arch" dependency for this driver is !BIG_ENDIAN, but
> unfortunately
> we don't have a generic Kconfig symbol for that.
> Perhaps we may want to introduce that?
> Of course we prefer to make drivers work on all endianness instead...

CONFIG_VIRT_TO_BUS is certainly also a dependency, since it fails
to build without that. I think we can address the two problems separately.

David Howells brought up the topic of endian checks recently, noting
that the way we define __BIG_ENDIAN and __LITTLE_ENDIAN in the kernel
is incompatible to how do it in user space, and not much better either.

A few architectures that are bi-endian (arc, arm, c6x, mips, sh) already
have CONFIG_CPU_IS_LITTLE_ENDIAN and CONFIG_CPU_IS_BIG_ENDIAN. I guess
it would be a good idea to provide these on all architectures.

	Arnd
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