From mboxrd@z Thu Jan  1 00:00:00 1970
From: catalin.marinas@arm.com (Catalin Marinas)
Date: Thu, 5 Feb 2015 10:41:49 +0000
Subject: [PATCH v8 02/21] acpi: fix acpi_os_ioremap for arm64
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To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Wed, Feb 04, 2015 at 06:58:14PM +0000, Mark Salter wrote:
> On Wed, 2015-02-04 at 17:57 +0000, Catalin Marinas wrote:
> > On Wed, Feb 04, 2015 at 04:08:27PM +0000, Mark Salter wrote:
> > > acpi_os_remap() is used to map ACPI tables. These tables may be in ram
> > > which are already included in the kernel's linear RAM mapping. So we
> > > need ioremap_cache to avoid two mappings to the same physical page
> > > having different caching attributes.
> > 
> > What's the call path to acpi_os_ioremap() on such tables already in the
> > linear mapping? I can see an acpi_map() function which already takes
> > care of the RAM mapping case but there are other cases where
> > acpi_os_ioremap() is called directly. For example,
> > acpi_os_read_memory(), can it be called on both RAM and I/O?
> 
> acpi_map() is the one I've seen.

By default, if should_use_kmap() is not patched for arm64, it translates
to page_is_ram(); acpi_map() would simply use a kmap() which returns the
current kernel linear mapping on arm64.

> I'm not sure about others.

Question for the ARM ACPI guys: what happens if you implement
acpi_os_ioremap() on arm64 as just ioremap()? Do you get any WARN_ON()
(__ioremap_caller() checks whether the memory is RAM)?

-- 
Catalin