[PATCH v4] content: support SR-IOV

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

Allocate a feature bit for virtio devices which support SR-IOV.

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/11
---
More details can be found from this thread:
https://patchwork.kernel.org/patch/10285541/

v3 -> v4:
- Limit the feature to PCI devices with SR-IOV cap (MST);

v2 -> v3:
- Improve the wording (Cornelia);

v1 -> v2:
- s/Reserve/Allocate/ (MST);
- Add a Fixes tag (MST);
- Be more explicit in driver requirement (MST);
- Remove the "device MAY fail" description (MST);
- Rebase on IO_BARRIER patch;

RFC -> v1:
- Mention PCI in the description (Cornelia);

 content.tex | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/content.tex b/content.tex
index c4b3b5c..beec6c1 100644
--- a/content.tex
+++ b/content.tex
@@ -95,10 +95,10 @@ Feature bits are allocated as follows:
 \begin{description}
 \item[0 to 23] Feature bits for the specific device type
 
-\item[24 to 36] Feature bits reserved for extensions to the queue and
+\item[24 to 37] Feature bits reserved for extensions to the queue and
   feature negotiation mechanisms
 
-\item[37 and above] Feature bits reserved for future extensions.
+\item[38 and above] Feature bits reserved for future extensions.
 \end{description}
 
 \begin{note}
@@ -5365,6 +5365,9 @@ Descriptors} and \ref{sec:Packed Virtqueues / Indirect Flag: Scatter-Gather Supp
   better performance.  This feature indicates whether
   a stronger form of barrier suitable for hardware
   devices is necessary.
+  \item[VIRTIO_F_SR_IOV(37)] This feature indicates that
+  the device supports Single Root I/O Virtualization.
+  Currently only PCI devices support this feature.
 \end{description}
 
 \drivernormative{\section}{Reserved Feature Bits}{Reserved Feature Bits}
@@ -5384,6 +5387,16 @@ A driver SHOULD accept VIRTIO_F_IO_BARRIER if it is offered.
 If VIRTIO_F_IO_BARRIER has been negotiated, a driver MUST use
 the barriers suitable for hardware devices.
 
+If VIRTIO_F_SR_IOV has been negotiated, a driver can enable
+virtual functions through the device's PCI SR-IOV capability
+structure.  A driver MUST NOT negotiate VIRTIO_F_SR_IOV if
+the device does not have a PCI SR-IOV capability structure
+or is not a PCI device.  A driver MUST negotiate
+VIRTIO_F_SR_IOV and complete the feature negotiation
+(including setting the DRIVER_OK \field{status} bit) before
+enabling virtual functions through the device's PCI SR-IOV
+capability structure.
+
 \devicenormative{\section}{Reserved Feature Bits}{Reserved Feature Bits}
 
 A device MUST offer VIRTIO_F_VERSION_1.  A device MAY fail to operate further
@@ -5400,6 +5413,10 @@ buffers in the same order in which they have been available.
 A device MAY fail to operate further if VIRTIO_F_IO_BARRIER
 is not accepted.
 
+A device SHOULD offer VIRTIO_F_SR_IOV if it is a PCI device
+and presents a PCI SR-IOV capability structure, otherwise
+it MUST NOT offer VIRTIO_F_SR_IOV.
+
 \section{Legacy Interface: Reserved Feature Bits}\label{sec:Reserved Feature Bits / Legacy Interface: Reserved Feature Bits}
 
 Transitional devices MAY offer the following:
-- 
2.17.0