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

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Message-ID: <20070918232546.004af9ff@the-village.bc.nu>
Date:	Tue, 18 Sep 2007 23:25:46 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"Luis R. Rodriguez" <mcgrof@...il.com>,
	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

> 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.

Another reason we should enforce the use of ioread/iowrite is that some
platforms do daft things like map mmio type devices through indirect
register access. Sparc PCMCIA is a classic example. The only sane way to
make these work is to require ioread/iowrite is used with iomap

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