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Re: [Xen-devel] [PATCH RFC 02/35] xen: arm64: ACPI: Support common ACPI drivers

Hi Ian,

On 05/02/2015 19:04, Ian Campbell wrote:
On Wed, 2015-02-04 at 17:36 +0000, Julien Grall wrote:
I remembered to have a discussion about this change with Naresh few
month ago.

__va should only be used when the memory is direct-mapped to Xen (i.e
accessible directly). On ARM64, this only the case for the RAM. Can you
confirm that ACPI will always reside to the RAM?

Even if the answer is yes then rather than adding loads of ifdefs it
seems like the right thing would be to implement __acpi_map_table on
ARM, even if the implementation ends up being only return __va(phys).

Futhermore, the code of this function seems x86-specific. The low 1MB
may not be mapped on ARM64.

I would move the whole function (acpi_os_map_memory) per-architecture.

That's an option too, since once the "/* The low first Mb is always
mapped. */" bit is removed (which it should be since it is x86 specific)
then there isn't much left.

Assuming that the ACPI always resides in RAM, the vmap would be irrelevant for ARM64, and a waste of memory.

So it would be better to move the acp_os_map_memory per-architecture. IIRC it's what they choose in the ACPI series.


Julien Grall

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