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+QEMU<->ACPI BIOS memory hotplug interface
+--------------------------------------
+
+ACPI BIOS GPE.3 handler is dedicated for notifying OS about memory hot-add
+events.
+
+Memory hot-plug interface (IO port 0xa00-0xa17, 1-4 byte access):
+---------------------------------------------------------------
+0xa00:
+ read access:
+ [0x0-0x3] Lo part of memory device phys address
+ [0x4-0x7] Hi part of memory device phys address
+ [0x8-0xb] Lo part of memory device size in bytes
+ [0xc-0xf] Hi part of memory device size in bytes
+ [0x10-0x13] Memory device proximity domain
+ [0x14] Memory device status fields
+ bits:
+ 0: Device is enabled and may be used by guest
+ 1: Device insert event, used to distinguish device for which
+ no device check event to OSPM was issued.
+ It's valid only when bit 1 is set.
+ 2-7: reserved and should be ignored by OSPM
+ [0x15-0x17] reserved
+
+ write access:
+ [0x0-0x3] Memory device slot selector, selects active memory device.
+ All following accesses to other registers in 0xa00-0xa17
+ region will read/store data from/to selected memory device.
+ [0x4-0x7] OST event code reported by OSPM
+ [0x8-0xb] OST status code reported by OSPM
+ [0xc-0x13] reserved, writes into it are ignored
+ [0x14] Memory device control fields
+ bits:
+ 0: reserved, OSPM must clear it before writing to register
+ 1: if set to 1 clears device insert event, set by OSPM
+ after it has emitted device check event for the
+ selected memory device
+ 2-7: reserved, OSPM must clear them before writing to register
+
+Selecting memory device slot beyond present range has no effect on platform:
+ - write accesses to memory hot-plug registers not documented above are
+ ignored
+ - read accesses to memory hot-plug registers not documented above return
+ all bits set to 1.