linux-kernel - Re: [PATCH] arch/tile: new multi-core architecture for Linux

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Date:	Thu, 27 May 2010 22:48:10 +0900
From:	Paul Mundt <lethal@...ux-sh.org>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Chris Metcalf <cmetcalf@...era.com>, Arnd Bergmann <arnd@...db.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH] arch/tile: new multi-core architecture for Linux

On Thu, May 27, 2010 at 03:41:44PM +0200, Geert Uytterhoeven wrote:
> On Thu, May 27, 2010 at 15:30, Chris Metcalf <cmetcalf@...era.com> wrote:
> > On 5/27/2010 4:41 AM, Arnd Bergmann wrote:
> >> On Thursday 27 May 2010, Chris Metcalf wrote:
> >>>> +EXPORT_SYMBOL(inb);
> >>>>
> >>>> If you just remove these definitions, you get a link error for any
> >>>> driver that tries to use these, which is probably more helpful than
> >>>> the panic.
> >>>>
> >>>> OTOH, are you sure that you can't just map the PIO calls to mmio functions
> >>>> like readb plus some fixed offset? On most non-x86 architectures, the PIO
> >>>> area of the PCI bus is just mapped to a memory range somewhere.
> >>>>
> >>>>
> >>> I'll try to remove them and see if anything falls over. ??We don't have
> >>> any memory-mapped addresses in the 32-bit architecture, though that
> >>> changes with the 64-bit architecture, which introduces IO mappings. ??For
> >>> PCI we actually have to do a hypervisor transaction for reads or writes.
> >>>
> >> Ok, then I assume that PIO would also be a hypervisor call, right?
> >> If you don't have MMIO on 32 bit, you might want to not define either
> >> PIO (inb, ...) no MMIO (readb, ...) calls there and disable
> >> CONFIG_HAVE_MMIO in Kconfig.
> >>
> >
> > We don't define CONFIG_HAVE_MMIO, but drivers certainly seem to use
> > ioread/iowrite methods as well as inb/outb without guarding them with
> > any particular tests, so we have to provide definitions of some kind for
> > all of them. ??I'll confer with our PCI developer to see if we can clean
> > up the set of definitions in io.h.
> 
> It's CONFIG_NO_IOMEM (cfr. s390 and um), which is inverted and turned into
> CONFIG_HAS_IOMEM, to be checked by drivers.
> 
Likewise for CONFIG_NO_IOPORT for disabling PIO, although you'll probably
want to conditionalize this on PCI I/O.
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