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Message-ID: <dd16b9f3bad847b0eadc7f94368e27982c1a7560.1304541919.git.mst@redhat.com>
Date: Wed, 4 May 2011 23:51:38 +0300
From: "Michael S. Tsirkin" <mst@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: Rusty Russell <rusty@...tcorp.com.au>,
Carsten Otte <cotte@...ibm.com>,
Christian Borntraeger <borntraeger@...ibm.com>,
linux390@...ibm.com, Martin Schwidefsky <schwidefsky@...ibm.com>,
Heiko Carstens <heiko.carstens@...ibm.com>,
Shirley Ma <xma@...ibm.com>, lguest@...ts.ozlabs.org,
linux-kernel@...r.kernel.org,
virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
linux-s390@...r.kernel.org, kvm@...r.kernel.org,
Krishna Kumar <krkumar2@...ibm.com>,
Tom Lendacky <tahm@...ux.vnet.ibm.com>, steved@...ibm.com,
habanero@...ux.vnet.ibm.com
Subject: [PATCH 08/18] virtio_ring: support for used_event idx feature
Add support for the used_event idx feature: when enabling
interrupts, publish the current avail index value to
the host so that we get interrupts on the next update.
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
---
drivers/virtio/virtio_ring.c | 14 ++++++++++++++
1 files changed, 14 insertions(+), 0 deletions(-)
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 507d6eb..3a3ed75 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -320,6 +320,14 @@ void *virtqueue_get_buf(struct virtqueue *_vq, unsigned int *len)
ret = vq->data[i];
detach_buf(vq, i);
vq->last_used_idx++;
+ /* If we expect an interrupt for the next entry, tell host
+ * by writing event index and flush out the write before
+ * the read in the next get_buf call. */
+ if (!(vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT)) {
+ vring_used_event(&vq->vring) = vq->last_used_idx;
+ virtio_mb();
+ }
+
END_USE(vq);
return ret;
}
@@ -341,7 +349,11 @@ bool virtqueue_enable_cb(struct virtqueue *_vq)
/* We optimistically turn back on interrupts, then check if there was
* more to do. */
+ /* Depending on the VIRTIO_RING_F_USED_EVENT_IDX feature, we need to
+ * either clear the flags bit or point the event index at the next
+ * entry. Always do both to keep code simple. */
vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
+ vring_used_event(&vq->vring) = vq->last_used_idx;
virtio_mb();
if (unlikely(more_used(vq))) {
END_USE(vq);
@@ -468,6 +480,8 @@ void vring_transport_features(struct virtio_device *vdev)
break;
case VIRTIO_RING_F_INDIRECT_DESC:
break;
+ case VIRTIO_RING_F_USED_EVENT_IDX:
+ break;
default:
/* We don't understand this bit. */
clear_bit(i, vdev->features);
--
1.7.5.53.gc233e
--
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