On Sat, Jan 28, 2012 at 5:58 PM, Huang Ying <ying.huang@xxxxxxxxx> 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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