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Date: Thu, 13 Dec 2007 20:17:14 -0800 From: Roland Dreier <rdreier@...co.com> To: venkatesh.pallipadi@...el.com Cc: ak@....de, ebiederm@...ssion.com, torvalds@...ux-foundation.org, gregkh@...e.de, airlied@...net.ie, davej@...hat.com, mingo@...e.hu, tglx@...utronix.de, hpa@...or.com, akpm@...ux-foundation.org, arjan@...radead.org, jesse.barnes@...el.com, linux-kernel@...r.kernel.org, Suresh Siddha <suresh.b.siddha@...el.com> Subject: Re: [RFC PATCH 06/12] PAT 64b: Add ioremap_wc support > --- linux-2.6.24-rc4.orig/include/asm-x86/io_64.h 2007-12-11 14:24:56.000000000 -0800 > +++ linux-2.6.24-rc4/include/asm-x86/io_64.h 2007-12-11 15:49:52.000000000 -0800 > @@ -142,7 +142,8 @@ > * it's useful if some control registers are in such an area and write combining > * or read caching is not desirable: > */ > -extern void __iomem * ioremap_nocache (unsigned long offset, unsigned long size); > +extern void __iomem * ioremap_nocache(unsigned long offset, unsigned long size); > +extern void __iomem * ioremap_wc(unsigned long offset, unsigned long size); 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. Also I didn't see anything like pgprot_wc() in the patchset (although I just skimmed quickly for now). The use case I actually have would be in a a driver's .mmap method, where I want to map device registers into userspace with write-combining turned on: vma->vm_page_prot = pgprot_wc(vma->vm_page_prot); io_remap_pfn_range(vma, vma->vm_start, pfn, PAGE_SIZE, vma->vm_page_prot); where the pfn points into a PCI BAR (which will only be mapped once, so no issues with conflicting PATs or anything like that). - R. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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