QEMU<->ACPI BIOS PCI hotplug interface
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QEMU supports PCI hotplug via ACPI, for PCI bus 0. This document
describes the interface between QEMU and the ACPI BIOS.

ACPI GPE block (IO ports 0xafe0-0xafe3, byte access):
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Generic ACPI GPE block. Bit 1 (GPE.1) used to notify PCI hotplug/eject
event to ACPI BIOS, via SCI interrupt.

PCI slot injection notification pending (IO port 0xae00-0xae03, 4-byte access):
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Slot injection notification pending. One bit per slot.

Read by ACPI BIOS GPE.1 handler to notify OS of injection
events.  Read-only.

PCI slot removal notification (IO port 0xae04-0xae07, 4-byte access):
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Slot removal notification pending. One bit per slot.

Read by ACPI BIOS GPE.1 handler to notify OS of removal
events.  Read-only.

PCI device eject (IO port 0xae08-0xae0b, 4-byte access):
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Write: Used by ACPI BIOS _EJ0 method to request device removal.
One bit per slot.

Read: Hotplug features register.  Used by platform to identify features
available.  Current base feature set (no bits set):
 - Read-only "up" register @0xae00, 4-byte access, bit per slot
 - Read-only "down" register @0xae04, 4-byte access, bit per slot
 - Read/write "eject" register @0xae08, 4-byte access,
   write: bit per slot eject, read: hotplug feature set
 - Read-only hotplug capable register @0xae0c, 4-byte access, bit per slot

PCI removability status (IO port 0xae0c-0xae0f, 4-byte access):
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Used by ACPI BIOS _RMV method to indicate removability status to OS. One
bit per slot.  Read-only