Re: [PATCH] revert ath5k ioread32()/iowrite32() usage - use readl()/writel(), we're MMIO-only

["Luis R. Rodriguez" <mcgrof@gmail.com>]

On 9/17/07, Jiri Slaby <jirislaby@gmail.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@pobox.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