linux-kernel - Re: [PATCH] Clarify pci_iomap() usage for MMIO-only devices

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Date:	Tue, 18 Sep 2007 15:07:23 -0400
From:	"Luis R. Rodriguez" <mcgrof@...il.com>
To:	"Linus Torvalds" <torvalds@...ux-foundation.org>
Cc:	"Alan Cox" <alan@...rguk.ukuu.org.uk>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"Jeff Garzik" <jeff@...zik.org>,
	"John W. Linville" <linville@...driver.com>,
	linux-wireless <linux-wireless@...r.kernel.org>
Subject: Re: [PATCH] Clarify pci_iomap() usage for MMIO-only devices

On 9/18/07, Linus Torvalds <torvalds@...ux-foundation.org> wrote:
>
>
> On Tue, 18 Sep 2007, Luis R. Rodriguez wrote:
> >
> > Alright, here is the same patch inline with s/recommended/required/ language:
>
> Well, the thing is, I'm not at all sure that I agree with this.
>
> If you use ioport_map/unmap, then you really *should* access them with the
> proper iomem accessors (ioread/iowrite). The fact that it may happen to
> work (when using the default lib/iomap.c implementation, at least) on
> some architectures and with the current implementation still doesn't mean
> that you should necessarily use readb/writeb.
>
> After all, you cannot use "inb/outb" on it, even if would happen to be an
> IO address.
>
> So what is this usage that wants to use the bogus accessor? Why not fix
> that instead of adding documentation for something that is very arguably
> something we want to *avoid* having people do!

ACK -- driver developers use this just to save themselves a few lines
from calling pci_resource_start() and friends. How about having an
inline which does what pci_iomap() does except it doesn't call
ioport_map() ? I am just not sure where this would go..

  Luis
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