The current MMIO transport layer uses a single, dedicated interrupt
signal, which brings performance penalty. Add a feature bit (40)
for introducing MSI capability.

Co-developed-by: Chao Peng <chao.p.peng@linux.intel.com>
Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
Co-developed-by: Liu Jiang <gerry@linux.alibaba.com>
Signed-off-by: Liu Jiang <gerry@linux.alibaba.com>
Co-developed-by: Zha Bin <zhabin@linux.alibaba.com>
Signed-off-by: Zha Bin <zhabin@linux.alibaba.com>
Signed-off-by: Jing Liu <jing2.liu@linux.intel.com>
---
 content.tex | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/content.tex b/content.tex
index 5881253..ff151ba 100644
--- a/content.tex
+++ b/content.tex
@@ -5840,6 +5840,9 @@ \chapter{Reserved Feature Bits}\label{sec:Reserved Feature Bits}
   \item[VIRTIO_F_MMIO_NOTIFICATION(39)] This feature indicates
   that the device supports enhanced notification mechanism on
   MMIO transport layer.
+  \item[VIRTIO_F_MMIO_MSI(40)] This feature indicates that the
+  device supports Message Signal Interrupts (MSI) mechanism on
+  MMIO transport layer.
 
 \drivernormative{\section}{Reserved Feature Bits}{Reserved Feature Bits}
 
@@ -5875,6 +5878,10 @@ \chapter{Reserved Feature Bits}\label{sec:Reserved Feature Bits}
 
 A driver SHOULD accept VIRTIO_F_MMIO_NOTIFICATION if it is offered.
 
+A driver SHOULD accept VIRTIO_F_MMIO_MSI if it is offered.
+If VIRTIO_F_MMIO_MSI has been negotiated, a driver MUST try to
+set up MSI at first priority.
+
 \devicenormative{\section}{Reserved Feature Bits}{Reserved Feature Bits}
 
 A device MUST offer VIRTIO_F_VERSION_1.  A device MAY fail to operate further
-- 
2.7.4