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

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Date:	Thu, 27 May 2010 15:41:44 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Chris Metcalf <cmetcalf@...era.com>
Cc:	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 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.

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds
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