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

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Date:	Tue, 18 Sep 2007 17:30:46 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	"Luis R. Rodriguez" <mcgrof@...il.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel <linux-kernel@...r.kernel.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

Linus Torvalds wrote:
> The old situation with SATA drivers that had
> 
> 	if (iomem)
> 		writel(..)
> 	else
> 		outl(..)
> 
> in the cases that needed it (and used hardcoded writel/outl in the cases 
> that didn't) was an example of code that "in theory" is faster. But 
> dammit, in practice that mattered not one whit, and what iomap() tries to 
> do is to attack the _real_ problem we had in that area. 
> 
> Which had nothing what-so-ever to do with any branches.

And none of those issues are a factor at all in ath5k (which spawned 
this sub-discussion), or indeed many other drivers.  The above code you 
cite is -generic-, hardware agnostic code.

Most new hardware is MMIO-only, making ioread32() only for drivers that 
care about legacy IO support, something that is being slowly phased out. 
  e.g. legacy IDE, legacy 10/100 mbps ethernet NICs with the dual 
MMIO/PIO register spaces.

	Jeff



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