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Subject: Re: [PATCH] EFI: Do not use __pa() to get the physical address of
 an ioremapped memory range
From: Matt Fleming <matt@console-pimps.org>
To: huang ying <huang.ying.caritas@gmail.com>
Cc: Zhang Rui <rui.zhang@intel.com>, LKML <linux-kernel@vger.kernel.org>,
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Date: Wed, 14 Sep 2011 20:16:50 +0100
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On Tue, 2011-09-13 at 16:48 +0800, huang ying wrote:
> On Mon, Sep 12, 2011 at 10:52 PM, Matt Fleming <matt@console-pimps.org> wrote:
> > On Fri, 2011-09-02 at 13:12 +0800, huang ying wrote:
> >> On Thu, Sep 1, 2011 at 8:28 PM, Matt Fleming <matt@console-pimps.org> wrote:
> >> >
> >> > Hmm.. does anyone know why we ioremap_cache() the memory on
> >> > CONFIG_X86_32 instead of ioremap_nocache()? In the case of
> >> > EFI_MEMORY_MAPPED_IO the memory really needs to be uncached. Then if
> >> > we've ioremap'd the memory we should skip set_memory_uc() altogether,
> >> > no?
> >>
> >> Because whether the mapping should be cached is determined by md->attr
> >> instead of md->type.  And besides UC, we may add WC, etc support.
> >
> > Confused.
> >
> > The CONFIG_X86_64 version of efi_ioremap() looks like this,
> >
> > void __iomem *__init efi_ioremap(unsigned long phys_addr, unsigned long size,
> >                                 u32 type)
> > {
> >        unsigned long last_map_pfn;
> >
> >        if (type == EFI_MEMORY_MAPPED_IO)
> >                return ioremap(phys_addr, size);
> >
> > Which uses md->type to figure out if we should call ioremap(), which on
> > x86 is #define'd to ioremap_nocache(). CONFIG_X86_32 doesn't do this,
> > but it looks to me like it should.
> 
> I don't think this type based solution is the perfect one.

Why? What else would you suggest?

-- 
Matt Fleming, Intel Open Source Technology Center