linux-kernel - Re: [patch] x86, voyager: fix ioremap

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Date:	Sun, 27 Apr 2008 18:53:33 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	David Miller <davem@...emloft.net>
CC:	James.Bottomley@...senPartnership.com, mingo@...e.hu,
	tglx@...utronix.de, linux-kernel@...r.kernel.org, hpa@...or.com,
	torvalds@...ux-foundation.org
Subject: Re: [patch] x86, voyager: fix ioremap_nocache()

David Miller wrote:
> From: Jeff Garzik <jeff@...zik.org>
> Date: Sun, 27 Apr 2008 18:39:24 -0400
> 
>> I disagree with this semantics change.  A number of code places _and 
>> drivers_ GET IT RIGHT, and these are all broken now?
> 
> [ Note, James's patch that you quoted is about mapping DMA
>   memory, in dma_declare_coherent_memory(), rather than devices.
>   But I know what you are trying to talk about Jeff. :-) ]
> 
> Wrt. ioremap() semanics, it is important to realize that if
> the implementation of this on x86 has been giving non-cached
> I/O mappings out up until recently, you can expect that there
> are hundreds of drivers that might now be broken.
> 
> That's the sad fact of the ubiquity of x86, and it doesn't matter how
> we defined the API is some document.
> 
> Anyways, my point is that this angle should be strongly considered in
> any discussion about ioremap() behavior.

Understood.

I guess I am more annoyed that this stealth semantics change appears to 
have broken everything that depends on pci_iomap(), including 90%+ of 
all libata drivers, unless I am missing something.

That one piece of code (pci_iomap) was correct under the old semantics, 
on x86 and elsewhere.  It's tested and working nicely, and depended upon 
by many drivers.

	Jeff



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