linux-kernel - Re: [PATCH] revert ath5k ioread32()/iowrite32() usage

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Date:	Tue, 18 Sep 2007 15:03:48 -0400
From:	"Luis R. Rodriguez" <mcgrof@...il.com>
To:	"Jiri Slaby" <jirislaby@...il.com>
Cc:	"Jeff Garzik" <jeff@...zik.org>,
	"John W. Linville" <linville@...driver.com>,
	linux-wireless <linux-wireless@...r.kernel.org>,
	"Alan Cox" <alan@...rguk.ukuu.org.uk>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] revert ath5k ioread32()/iowrite32() usage - use readl()/writel(), we're MMIO-only

On 9/17/07, Jiri Slaby <jirislaby@...il.com> wrote:
> On 09/17/2007 10:59 PM, Jeff Garzik wrote:
> > Jiri Slaby wrote:
> >> NACK, this is wrong. iomap returns platform dependant return value,
> >> which may or
> >
> > Incorrect.  readl() and writel() work just fine on all existing
> > platforms where Atheros may be used.
>
> Ok, this is what Alan Cox wrote about that and you didn't reply to it, so I
> thought he's right. Anyway I wouldn't rely on iomap that it will never be
> changed even on x86 -- what's the (performance) impact of having ioread instead
> of readl? How much data are transferred this way?
>
> <cite from="http://lkml.org/lkml/2007/8/25/50">
> On Sat, 25 Aug 2007 04:56:19 -0400
> Jeff Garzik <jgarzik@...ox.com> wrote:
>
> > If the driver knows its MMIO, using readX/writeX after pci_iomap() is
> > just fine, for all current implementations, and it makes sense that way.
>
> There is nothing that guarantees this is permitted, any more than there
> is anything saying not to use outb/outl. Some of the implementations do
> quite strange things. It may happen to work but its not in the
> documentation or the comments.

I posted a patch to update the documentation with this.

> Please, can anybody clarify it?

Based on Alan's 'Review-by' remarks on my patch for updating the
documenation on pci_iomap() it seems this validates this patch. Please
see thread with subject:

[PATCH] Clarify pci_iomap() usage for MMIO-only devices

   Luis
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