[PATCH v7 13/13] newdevice: Extend informative guidance on capabilities, resources

[Parav Pandit <parav@nvidia.com>]

Add few informative guidance/notes about which use cases to use
device capabilities, and device resources.

Fixes: https://github.com/oasis-tcs/virtio-spec/issues/179
Signed-off-by: Parav Pandit <parav@nvidia.com>
---
 newdevice.tex | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/newdevice.tex b/newdevice.tex
index 93feb71..fc10632 100644
--- a/newdevice.tex
+++ b/newdevice.tex
@@ -26,6 +26,29 @@ \section{What Device Configuration Space Layout?}\label{sec:Creating New Device
 writable by the driver.  Therefore, no writeable field which triggers an
 action ought to be wider than 32 bits.
 
+\section{When to use Device Resource?}\label{sec:Creating New Device Types or Extending the Device / When to use Device Resource?}
+For a desired functionality if majority of fields are configured by the
+driver, or if device sets majority of fields which are changing often and
+driver wants to query them, in both of those cases, using a device
+resource is preferred.
+
+Even if such functionality is limited to small count as small as one,
+using a device resource can be helpful with large number of devices.
+
+\section{When to use the Capabilities?}\label{sec:Creating New Device Types or Extending the Device / When to use the Capabilities?}
+Any field which is more than a bit that a device want to expose to the
+driver, can be exposed as a device capability. Device and driver
+capabilities are not constantly changing fields during the life cycle
+of the driver and device; capabilities are rarely changing parameters
+used during the life time of driver possibly dynamically. Sometimes a
+system may have many similar devices, but each device may have different
+attributes, it is better to use capabilities for such attributes as well.
+
+\section{Read only attributes as capabilities?}\label{sec:Creating New Device Types or Extending the Device / Read only attributes as capabilities?}
+If there are one or more device attributes which are read only for the driver,
+they can also be used as device capabilities. They must be documented as
+read only so that driver do not try to change them.
+
 \section{What Device Number?}\label{sec:Creating New Device Types or Extending the Device / What Device Number?}
 
 Device numbers for the new devices can be reserved by the OASIS committee: email
-- 
2.34.1