virtio: Formally reserve bits 28-31 to be 'transport' features.
We assign feature bits as required, but it makes sense to reserve some
for the particular transport, rather than the particular device.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index fc85cba..baf1033 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -113,6 +113,11 @@
set_bit(f, dev->features);
}
+ /* Transport features are always preserved to pass to set_features. */
+ for (i = VIRTIO_TRANSPORT_F_START; i < VIRTIO_TRANSPORT_F_END; i++)
+ if (device_features & (1 << i))
+ set_bit(i, dev->features);
+
err = drv->probe(dev);
if (err)
add_status(dev, VIRTIO_CONFIG_S_FAILED);
diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index 7eb4b34..5a30cfb 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -18,6 +18,12 @@
/* We've given up on this device. */
#define VIRTIO_CONFIG_S_FAILED 0x80
+/* Some virtio feature bits (currently bits 28 through 31) are reserved for the
+ * transport being used (eg. virtio_ring), the rest are per-device feature
+ * bits. */
+#define VIRTIO_TRANSPORT_F_START 28
+#define VIRTIO_TRANSPORT_F_END 32
+
/* Do we get callbacks when the ring is completely used, even if we've
* suppressed them? */
#define VIRTIO_F_NOTIFY_ON_EMPTY 24