Re: [PATCH 0/7] ACPI: Memory Mapped I/O (MMIO) pre-mapping

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On Fri, 2010-10-22 at 10:57 +0800, Huang, Ying wrote:
> On Fri, 2010-10-22 at 10:43 +0800, Li, Shaohua wrote:
> > On Fri, 2010-10-22 at 04:23 +0800, Myron Stowe wrote:
> > > ACPI's system event related IRQ handing accesses specific fixed
> > > hardware registers; namely PM1a event, PM1b event, GPE0, and GPE1
> > > which are declared in the FADT.  If these registers are backed by
> > > MMIO, as opposed to I/O port space, accessing them within interrupt
> > > context will incur a panic since acpi_read() and acpi_write() end up
> > > calling ioremap(), which may block to allocate memory - BZ 18012.
> > since you just access several bytes mmio in interrupt context, can't you
> > use kmap_atomic_pfn() here?
> 
> On x86_64, kmap_atomic_pfn() is defined as kmap_atomic(), which requires
> struct page for the physical address. But the MMIO address may have no
> struct page.
ok, can we add a new entry in fix map and the entry is dedicated for
mmio mapping? The ioremap list looks like a hack.

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