[Qemu-devel] [RFC PATCH] spapr-vty: workaround "reg" property for old kernels

[Alexey Kardashevskiy <aik@ozlabs.ru>]

Old kernels (< 3.1) handle hvcX devices different in different parts.
Sometime the kernel assumes that the hvc device numbers start from zero
and if there is just one hvc, then it is hvc0.

However kernel's add_preferred_console() uses the very last byte of
the VTY's "reg" property as an hvc number so it might end up with something
different than hvc.

The problem appears on SLES11SP3 and RHEL6. If to run QEMU without
-nodefaults, then the default VTY is created first on a VIO bus and gets
reg==0x71000000 so it will be hvc0 and everything will be fine.
If to run QEMU with:
 -nodefaults \
 -chardev "socket,id=char1,host=localhost,port=8001,server,telnet,mux=on" \
 -device "spapr-vty,chardev=char1" \
 -mon "chardev=char1,mode=readline,id=mon1" \

then the exactly the same config is expected but in this case spapr-vty
gets reg==0x71000001 and therefore it becomes hvc1 and lots of debug
output is missing. SLES11SP3 does not even boot as /dev/console is
redirected to /dev/hvc0 which is dead.

The issue can be solved by manual selection of VTY's "reg" property to
have last byte equal to zero.

The alternative would be to use separate "reg" property counter for
automatic "reg" property generation and this is what the patch does.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---

Since libvirt uses "-nodefault" a lot and in this case "spapr-nvram" gets
created first and gets reg=0x71000000, we cannot just ignore this. Also,
it does not seem an option to require libvirt users to specify spapr-vty
"reg" property every time.

Can anyone think of a simpler solutionu? Thanks.


---
 hw/ppc/spapr_vio.c         | 7 ++++++-
 include/hw/ppc/spapr_vio.h | 1 +
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/hw/ppc/spapr_vio.c b/hw/ppc/spapr_vio.c
index a6a0a51..2d56950 100644
--- a/hw/ppc/spapr_vio.c
+++ b/hw/ppc/spapr_vio.c
@@ -438,7 +438,11 @@ static int spapr_vio_busdev_init(DeviceState *qdev)
         VIOsPAPRBus *bus = DO_UPCAST(VIOsPAPRBus, bus, dev->qdev.parent_bus);
 
         do {
-            dev->reg = bus->next_reg++;
+            if (!object_dynamic_cast(OBJECT(qdev), "spapr-vty")) {
+                dev->reg = bus->next_reg++;
+            } else {
+                dev->reg = bus->next_vty_reg++;
+            }
         } while (reg_conflict(dev));
     }
 
@@ -501,6 +505,7 @@ VIOsPAPRBus *spapr_vio_bus_init(void)
     qbus = qbus_create(TYPE_SPAPR_VIO_BUS, dev, "spapr-vio");
     bus = DO_UPCAST(VIOsPAPRBus, bus, qbus);
     bus->next_reg = 0x71000000;
+    bus->next_vty_reg = 0x71000100;
 
     /* hcall-vio */
     spapr_register_hypercall(H_VIO_SIGNAL, h_vio_signal);
diff --git a/include/hw/ppc/spapr_vio.h b/include/hw/ppc/spapr_vio.h
index d8b3b03..3a92d9e 100644
--- a/include/hw/ppc/spapr_vio.h
+++ b/include/hw/ppc/spapr_vio.h
@@ -73,6 +73,7 @@ struct VIOsPAPRDevice {
 struct VIOsPAPRBus {
     BusState bus;
     uint32_t next_reg;
+    uint32_t next_vty_reg;
     int (*init)(VIOsPAPRDevice *dev);
     int (*devnode)(VIOsPAPRDevice *dev, void *fdt, int node_off);
 };
-- 
1.8.4.rc4