linux-kernel - RE: [patch 09/11] PAT x86: Add ioremap

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Date:	Thu, 10 Jan 2008 11:25:25 -0800
From:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
To:	"Andi Kleen" <andi@...stfloor.org>
Cc:	<ebiederm@...ssion.com>, <rdreier@...co.com>,
	<torvalds@...ux-foundation.org>, <gregkh@...e.de>,
	<airlied@...net.ie>, <davej@...hat.com>, <mingo@...e.hu>,
	<tglx@...utronix.de>, <hpa@...or.co>,
	<linux-kernel@...r.kernel.org>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>
Subject: RE: [patch 09/11] PAT x86: Add ioremap_wc support


>-----Original Message-----
>From: Andi Kleen [mailto:andi@...stfloor.org] 
>Sent: Thursday, January 10, 2008 11:09 AM
>To: Pallipadi, Venkatesh
>Cc: ebiederm@...ssion.com; rdreier@...co.com; 
>torvalds@...ux-foundation.org; gregkh@...e.de; 
>airlied@...net.ie; davej@...hat.com; mingo@...e.hu; 
>tglx@...utronix.de; hpa@...or.co; 
>linux-kernel@...r.kernel.org; Siddha, Suresh B
>Subject: Re: [patch 09/11] PAT x86: Add ioremap_wc support
>
>venkatesh.pallipadi@...el.com writes:
>> Index: linux-2.6.git/include/asm-generic/iomap.h
>> ===================================================================
>> --- linux-2.6.git.orig/include/asm-generic/iomap.h	
>2008-01-08 03:31:37.000000000 -0800
>> +++ linux-2.6.git/include/asm-generic/iomap.h	
>2008-01-08 05:15:56.000000000 -0800
>> @@ -65,4 +65,8 @@
>>  extern void __iomem *pci_iomap(struct pci_dev *dev, int 
>bar, unsigned long max);
>>  extern void pci_iounmap(struct pci_dev *dev, void __iomem *);
>>  
>> +#ifndef ioremap_wc
>> +#define ioremap_wc ioremap_nocache
>> +#endif
>
>I don't think that's a good idea. Drivers should be able to 
>detect this somehow.
>Handling UC mappings as WC will probably give very poor results.
>

It is the other way. ioremap_wc aliases to ioremap_nocache.
This was based on earlier feedback from Roland.
>From: Roland Dreier [mailto:rdreier@...co.com] 
>I think ioremap_wc() needs to be available on all archs for this to be
>really useful to drivers.  It can be a fallback to ioremap_nocache()
>everywhere except 64-bit x86, but it's not nice for every driver that
>wants to use this to need an "#ifdef X86" or whatever.

Thanks,
Venki
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