From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ian Campbell <Ian.Campbell@citrix.com>
Subject: Re: [PATCH RFC 02/35] xen: arm64: ACPI: Support common
	ACPI drivers
Date: Thu, 5 Feb 2015 11:56:11 +0000
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To: Jan Beulich <JBeulich@suse.com>
Cc: Naresh Bhat <naresh.bhat@linaro.org>, Julien Grall <julien.grall@linaro.org>, tim@xen.org, xen-devel@lists.xen.org, stefano.stabellini@citrix.com, parth.dixit@linaro.org, christoffer.dall@linaro.org
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On Thu, 2015-02-05 at 11:34 +0000, Jan Beulich wrote:
> >> @@ -140,6 +145,7 @@ acpi_status acpi_os_write_port(acpi_io_address port, u32 value, u32 width)
> >>
> >>   	return AE_OK;
> >>   }
> >> +#endif
> > 
> > Why only x86? Linux seems to define it also for ARM64.
> 
> What is a port on ARM?

I don't know how common it is now, but on older ARM systems it wasn't
uncommon to reuse ISA type peripherals and the port space would be
mapped to a specific hardcoded MMIO region.

Even on modern h/w PCI host controllers have an MMIO region associated
with the I/O ports of the PCI cards on the bus.

All that said, I think it would be good to avoid doing anything with I/O
ports without a specific requirement arising from some h/w or the spec,
at least initially.

Ian.