Re: [PATCH v8 02/21] acpi: fix acpi_os_ioremap for arm64

[Mark Salter]

On Thu, 2015-02-05 at 10:41 +0000, Catalin Marinas wrote:
> 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.

The problem with kmap() is that it only maps a single page. I've seen
tables over 4k which is why I patched acpi_map() not to use kmap() 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)?
> 


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