Re: [Qemu-devel] [PATCH v2 2/6] s390x/vfio: ap: Use the APdevice as a child of the APBus

[Tony Krowiak]

On 11/29/18 6:45 AM, Cornelia Huck wrote:

On Thu, 22 Nov 2018 17:35:51 +0100
Pierre Morel <pmo...@linux.ibm.com> wrote:

Two good reasons to use the base device as a child of the
AP BUS:
- We can easily find the device without traversing the qtree.
- In case we have different APdevice instantiation, VFIO with
   interception or emulation, we will need the APDevice as
   a parent device.

Signed-off-by: Pierre Morel <pmo...@linux.ibm.com>
---
  hw/s390x/ap-device.c         | 22 ++++++++++++++++++++++
  hw/vfio/ap.c                 | 16 ++++++----------
  include/hw/s390x/ap-device.h |  2 ++
  3 files changed, 30 insertions(+), 10 deletions(-)

diff --git a/hw/s390x/ap-device.c b/hw/s390x/ap-device.c
index f5ac8db..554d5aa 100644
--- a/hw/s390x/ap-device.c
+++ b/hw/s390x/ap-device.c
@@ -11,13 +11,35 @@
  #include "qemu/module.h"
  #include "qapi/error.h"
  #include "hw/qdev.h"
+#include "hw/s390x/ap-bridge.h"
  #include "hw/s390x/ap-device.h"

+APDevice *s390_get_ap(void)

+{
+    static DeviceState *apb;
+    BusState *bus;
+    BusChild *child;
+    static APDevice *ap;
+
+    if (ap) {
+        return ap;
+    }
+
+    apb = s390_get_ap_bridge();
+    /* We have only a single child on the BUS */

So, there'll never a mixed environment? Or would that have a 'hybrid'
ap device?

It is not possible to have interpretation and interception. I suppose
one could mix emulated and virtual AP devices, but that seems highly
unlikely; in fact, I think it is highly unlikely that emulation is ever
implemented.

+    bus = qdev_get_child_bus(apb, TYPE_AP_BUS);
+    child = QTAILQ_FIRST(&bus->children);
+    assert(child != NULL);
+    ap = DO_UPCAST(APDevice, parent_obj, child->child);
+    return ap;
+}
+
  static void ap_class_init(ObjectClass *klass, void *data)
  {
      DeviceClass *dc = DEVICE_CLASS(klass);

dc->desc = "AP device class";

+    dc->bus_type = TYPE_AP_BUS;
      dc->hotpluggable = false;
  }

diff --git a/hw/vfio/ap.c b/hw/vfio/ap.c

index 65de952..94e5a1a 100644
--- a/hw/vfio/ap.c
+++ b/hw/vfio/ap.c
@@ -35,9 +35,6 @@ typedef struct VFIOAPDevice {
      VFIODevice vdev;
  } VFIOAPDevice;

-#define VFIO_AP_DEVICE(obj) \

-        OBJECT_CHECK(VFIOAPDevice, (obj), VFIO_AP_DEVICE_TYPE)

Hm?

I received a comment from Thomas Huth in Message ID
<2291104a-4cbf-e4fd-3496-fa0910beb...@redhat.com>
that DO_UPCAST should be avoided in new code. This macro
should probably be restored and an AP_DEVICE() macro added.

-
  static void vfio_ap_compute_needs_reset(VFIODevice *vdev)
  {
      vdev->needs_reset = false;