[Qemu-arm] [PATCH V10 9/9] pvpanic : update pvpanic document

[Peng Hao]

Add mmio support info in docs/specs/pvpanic.txt.

Signed-off-by: Peng Hao <address@hidden>
---
 docs/specs/pvpanic.txt | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/docs/specs/pvpanic.txt b/docs/specs/pvpanic.txt
index c7bbacc..b1beea3 100644
--- a/docs/specs/pvpanic.txt
+++ b/docs/specs/pvpanic.txt
@@ -1,14 +1,17 @@
 PVPANIC DEVICE
 ==============
 
-pvpanic device is a simulated ISA device, through which a guest panic
-event is sent to qemu, and a QMP event is generated. This allows
+pvpanic device is a simulated ISA/SYSBUS device, through which a guest
+panic event is sent to qemu, and a QMP event is generated. This allows
 management apps (e.g. libvirt) to be notified and respond to the event.
 
 The management app has the option of waiting for GUEST_PANICKED events,
 and/or polling for guest-panicked RunState, to learn when the pvpanic
 device has fired a panic event.
 
+The pvpanic device can be implemented as an ISA device (using IOPORT), 
+or, since qemu 4.0, as a SYSBUS device (using MMIO).
+
 ISA Interface
 -------------
 
@@ -19,6 +22,13 @@ Software should set only bits both itself and the device 
recognize.
 Currently, only bit 0 is recognized, setting it indicates a guest panic
 has happened.
 
+SYSBUS Interface
+----------------
+
+The SYSBUS interface is similar to the ISA interface except that it uses
+MMIO. For example, the arm virt machine could put the pvpanic device at
+[0x9070000, 0x9070001] and currently only the first byte is used.
+
 ACPI Interface
 --------------
 
-- 
1.8.3.1