[PATCH] content: enhance device requirements for feature bits

[Tiwei Bie <tiwei.bie@intel.com>]

Suggested-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
Fixes: https://github.com/oasis-tcs/virtio-spec/issues/14
---
 content.tex | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/content.tex b/content.tex
index f996fad..8374d3f 100644
--- a/content.tex
+++ b/content.tex
@@ -125,6 +125,13 @@ which was not offered.  The device SHOULD accept any valid subset
 of features the driver accepts, otherwise it MUST fail to set the
 FEATURES_OK \field{device status} bit when the driver writes it.
 
+If a device has successfully negotiated a set of features
+at least once (by setting the FEATURES_OK \field{device
+status} bit when the driver writes it), then it SHOULD NOT
+fail re-negotiation of the same set of features after a
+device or system reset.  Failure to do so would interfere
+with the resuming from suspend and error recovery.
+
 \subsection{Legacy Interface: A Note on Feature
 Bits}\label{sec:Basic Facilities of a Virtio Device / Feature
 Bits / Legacy Interface: A Note on Feature Bits}
-- 
2.17.0