[Qemu-devel] [PATCH] acpi: beginnings of piix acpi interface doc

["Michael S. Tsirkin" <mst@redhat.com>]

Before we start tweaking and enhancing hardware, I think
it makes sense to document what we currently have, to make
sure we stay compatible.
This documents the hotplug interface for piix.
Stubs for cpu hotplug, PM.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 docs/acpi.txt |   32 ++++++++++++++++++++++++++++++++
 1 files changed, 32 insertions(+), 0 deletions(-)
 create mode 100644 docs/acpi.txt

diff --git a/docs/acpi.txt b/docs/acpi.txt
new file mode 100644
index 0000000..4938d48
--- /dev/null
+++ b/docs/acpi.txt
@@ -0,0 +1,32 @@
+QEMU exposes the following registers to guests,
+intended primarily for use by the ACPI interface.
+
+PCI Hotplug
+----
+
+Events use the standard GPE register:
+GPE  0xafe0 - an ACPI GPE register
+
+Hotplug events set GPE bit 1 (mask 0x2)
+
+The following registers are used for PCI hotplug.
+Each register is 32 bit (4 bytes) long, and has little endian format.
+Bits 0-31 in each register correspond to slots 0-31 on the root bus,
+respectively.
+
+UP   0xae00 - RO - Bit set by host on device insertion (note:existing implementations
+                   trigger device check event)
+DOWN 0xae04 - RO - Bit set by host on user eject request
+EJ0  0xae08 - WO - Bit set by guest removes all power to device
+RMV  0xae0c - RO - Bit set by host if slot supports hotplug
+                   (can not change while guest is up)
+
+
+Power management
+----
+TODO
+
+
+CPU hotplug
+----
+TODO
-- 
1.7.9.111.gf3fb0