linux-kernel - Re: [PATCH-RFC 1/2] tile: don't panic on iomap

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Message-Id: <201111300909.18431.arnd@arndb.de>
Date:	Wed, 30 Nov 2011 09:09:18 +0000
From:	Arnd Bergmann <arnd@...db.de>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Chris Metcalf <cmetcalf@...era.com>,
	Lucas De Marchi <lucas.demarchi@...fusion.mobi>,
	Paul Mundt <lethal@...ux-sh.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	"David S. Miller" <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	linux-arch@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH-RFC 1/2] tile: don't panic on iomap

On Wednesday 30 November 2011, Michael S. Tsirkin wrote:
> 
> On Tue, Nov 29, 2011 at 10:05:11PM +0000, Arnd Bergmann wrote:
> > On Tuesday 29 November 2011, Michael S. Tsirkin wrote:
> > > diff --git a/arch/tile/include/asm/io.h b/arch/tile/include/asm/io.h
> > > index c9ea165..be6090d 100644
> > > --- a/arch/tile/include/asm/io.h
> > > +++ b/arch/tile/include/asm/io.h
> > > @@ -204,7 +204,8 @@ static inline long ioport_panic(void)
> > >  
> > >  static inline void __iomem *ioport_map(unsigned long port, unsigned int len)
> > >  {
> > > -       return (void __iomem *) ioport_panic();
> > > +       pr_info("Trying to map an IO resource - it does not exit on tile.\n");
> > > +       return NULL;
> > >  }
> > 
> > Why not just set CONFIG_NO_IOPORT and make this unavailable at compile time?
> > 
> >       Arnd
> 
> Well I think CONFIG_NO_IOPORT only has effect if you pull in asm-generic/io.h.
> This might work but I have no idea.

NO_IOPORT ha nothing to do with asm-generic, it just makes lib/iomap.c leave out
the calls to ioport_map, and prevent all drivers that call ioport_map from being
built.

> Presumably whoever wrote that architecture considered and discarded setting GENERIC_IOMAP.

The tile PCI controller is apparently special in that it does not map the
PIO region into MMIO space, or make it available in any other way, so generic
iomap with IOCOND is pointless. Setting NO_IPORT will still mean that drivers
using ioport_map will not be built. This mostly impacts the legacy (non-AHCI)
ATA controllers, which I assume are not used on tile anyway.

	Arnd
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