[PATCH RFC v5 18/19] virtio: support revision-specific features

[Cornelia Huck <cornelia.huck@xxxxxxxxxx>]

Devices may support different sets of feature bits depending on which
revision they're operating at. Let's give the transport a way to
re-query the device about its features when the revision has been
changed.

Signed-off-by: Cornelia Huck <cornelia.huck@xxxxxxxxxx>
---
 hw/s390x/virtio-ccw.c          |   12 ++++++++++--
 hw/virtio/virtio-bus.c         |   14 ++++++++++++--
 include/hw/virtio/virtio-bus.h |    3 +++
 include/hw/virtio/virtio.h     |    3 +++
 4 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/hw/s390x/virtio-ccw.c b/hw/s390x/virtio-ccw.c
index ec492b8..3826074 100644
--- a/hw/s390x/virtio-ccw.c
+++ b/hw/s390x/virtio-ccw.c
@@ -699,6 +699,10 @@ static int virtio_ccw_cb(SubchDev *sch, CCW1 ccw)
         }
         ret = 0;
         dev->revision = revinfo.revision;
+        /* Re-evaluate which features the device wants to offer. */
+        dev->host_features =
+            virtio_bus_get_vdev_features_rev(&dev->bus, dev->host_features,
+                                             dev->revision >= 1 ? 1 : 0);
         break;
     default:
         ret = -ENOSYS;
@@ -712,6 +716,9 @@ static void virtio_sch_disable_cb(SubchDev *sch)
     VirtioCcwDevice *dev = sch->driver_data;
 
     dev->revision = -1;
+    /* Reset the device's features to legacy. */
+    dev->host_features =
+        virtio_bus_get_vdev_features_rev(&dev->bus, dev->host_features, 0);
 }
 
 static int virtio_ccw_device_init(VirtioCcwDevice *dev, VirtIODevice *vdev)
@@ -854,8 +861,9 @@ static int virtio_ccw_device_init(VirtioCcwDevice *dev, VirtIODevice *vdev)
     virtio_add_feature(&dev->host_features, VIRTIO_F_NOTIFY_ON_EMPTY);
     virtio_add_feature(&dev->host_features, VIRTIO_F_BAD_FEATURE);
 
-    dev->host_features = virtio_bus_get_vdev_features(&dev->bus,
-                                                      dev->host_features);
+    /* All devices start in legacy mode. */
+    dev->host_features =
+        virtio_bus_get_vdev_features_rev(&dev->bus, dev->host_features, 0);
 
     css_generate_sch_crws(sch->cssid, sch->ssid, sch->schid,
                           parent->hotplugged, 1);
diff --git a/hw/virtio/virtio-bus.c b/hw/virtio/virtio-bus.c
index 32e3fab..a30826c 100644
--- a/hw/virtio/virtio-bus.c
+++ b/hw/virtio/virtio-bus.c
@@ -97,18 +97,28 @@ size_t virtio_bus_get_vdev_config_len(VirtioBusState *bus)
 }
 
 /* Get the features of the plugged device. */
-uint64_t virtio_bus_get_vdev_features(VirtioBusState *bus,
-                                      uint64_t requested_features)
+uint64_t virtio_bus_get_vdev_features_rev(VirtioBusState *bus,
+                                          uint64_t requested_features,
+                                          unsigned int revision)
 {
     VirtIODevice *vdev = virtio_bus_get_device(bus);
     VirtioDeviceClass *k;
 
     assert(vdev != NULL);
     k = VIRTIO_DEVICE_GET_CLASS(vdev);
+    if (revision > 0 && k->get_features_rev) {
+        return k->get_features_rev(vdev, requested_features, revision);
+    }
     assert(k->get_features != NULL);
     return k->get_features(vdev, requested_features);
 }
 
+uint64_t virtio_bus_get_vdev_features(VirtioBusState *bus,
+                                      uint64_t requested_features)
+{
+    return virtio_bus_get_vdev_features_rev(bus, requested_features, 0);
+}
+
 /* Get bad features of the plugged device. */
 uint64_t virtio_bus_get_vdev_bad_features(VirtioBusState *bus)
 {
diff --git a/include/hw/virtio/virtio-bus.h b/include/hw/virtio/virtio-bus.h
index 0a4dde1..f0916ef 100644
--- a/include/hw/virtio/virtio-bus.h
+++ b/include/hw/virtio/virtio-bus.h
@@ -84,6 +84,9 @@ size_t virtio_bus_get_vdev_config_len(VirtioBusState *bus);
 /* Get the features of the plugged device. */
 uint64_t virtio_bus_get_vdev_features(VirtioBusState *bus,
                                       uint64_t requested_features);
+uint64_t virtio_bus_get_vdev_features_rev(VirtioBusState *bus,
+                                          uint64_t requested_features,
+                                          unsigned int revision);
 /* Get bad features of the plugged device. */
 uint64_t virtio_bus_get_vdev_bad_features(VirtioBusState *bus);
 /* Get config of the plugged device. */
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index e7bedd1..f31e3df 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -147,6 +147,9 @@ typedef struct VirtioDeviceClass {
     DeviceRealize realize;
     DeviceUnrealize unrealize;
     uint64_t (*get_features)(VirtIODevice *vdev, uint64_t requested_features);
+    uint64_t (*get_features_rev)(VirtIODevice *vdev,
+                                 uint64_t requested_features,
+                                 unsigned int revision);
     uint64_t (*bad_features)(VirtIODevice *vdev);
     void (*set_features)(VirtIODevice *vdev, uint64_t val);
     int (*validate_features)(VirtIODevice *vdev);
-- 
1.7.9.5

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