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    SubjectRe: [PATCH 2/3] ACPI, APEI: Add RAM mapping support to ACPI
    On Sat, Jan 28, 2012 at 5:58 PM, Huang Ying <ying.huang@intel.com> wrote:
    > Hi, Bjorn,
    >
    > Sorry for late.  Just return from Chinese new year holiday.
    >
    > On Sat, 2012-01-21 at 08:04 -0700, Bjorn Helgaas wrote:
    > [snip]
    >> > +
    >> > +static void __iomem *acpi_map(acpi_physical_address pg_off, unsigned long pg_sz)
    >> > +{
    >> > +       unsigned long pfn;
    >> > +
    >> > +       pfn = pg_off >> PAGE_SHIFT;
    >> > +       if (should_use_kmap(pfn)) {
    >> > +               if (pg_sz > PAGE_SIZE)
    >> > +                       return NULL;
    >> > +               return (void __iomem __force *)kmap(pfn_to_page(pfn));
    >> > +       } else
    >> > +               return acpi_os_ioremap(pg_off, pg_sz);
    >>
    >> This implies that ioremap() works differently on ia64 than on x86.
    >> Apparently one can ioremap() RAM on x86, but not on ia64.  Why is this
    >> different?  Shouldn't we instead fix ioremap() on ia64 so it works the
    >> same as on x86?
    >
    > If my understanding were correct, ioremap can not work for RAM on x86.
    > So we need to use kmap for RAM.  And on IA64, ioremap works for RAM and
    > will take care of cache attributes while kmap will not.  So ioremap is
    > used on IA64, while kmap is used on x86.

    My point is that the *user* of ioremap() shouldn't need to care what
    architecture we're on. For example, maybe the ioremap()
    implementation could be changed so that it uses kmap() internally when
    necessary.

    >> I looked at the ia64 ioremap(), and I can't see the reason it fails
    >> for RAM.  Huang, do you remember the details from 76da3fb3575?

    This question is still open. Do you remember anything about it?

    Bjorn
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