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

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Message-ID: <481501CC.2040408@zytor.com>
Date:	Sun, 27 Apr 2008 15:44:28 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeff Garzik <jeff@...zik.org>
CC:	James Bottomley <James.Bottomley@...senPartnership.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [patch] x86, voyager: fix ioremap_nocache()

Jeff Garzik wrote:
> 
> Isn't there Yet More Breakage in lib/iomap.c, given these new semantics?
> 
>         if (flags & IORESOURCE_MEM) {
>                 if (flags & IORESOURCE_CACHEABLE)
>                         return ioremap(start, len);
>                 return ioremap_nocache(start, len);
>         }
> 
> Any driver using pci_iomap() (libata, and others) is affected.
> 
> I disagree with this semantics change.  A number of code places _and 
> drivers_ GET IT RIGHT, and these are all broken now?
> 

They don't, though.  They rely on the MTRRs to get it right for them, 
and the MTRRs will say "uncached" in nearly all cases.

Consider the case above: you would have gotten the same result 
*regardless*, because the MTRRs would not have made the memory 
cacheable.  Yes, it's broken, but it was broken before as well.

	-hpa
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