[PATCH] virtio-ccw: clarify some channel I/O concepts

[Cornelia Huck <cornelia.huck@de.ibm.com>]

Add the documents where channel I/O is generally described to the
normative references and add some further words on command rejects
and length checks.

Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>

---

These should hopefully specify clear enough what devices/drivers are
supposed to do with different commands. Any comments?
---
 virtio-v1.0-wd01-part1-specification.txt |   21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/virtio-v1.0-wd01-part1-specification.txt b/virtio-v1.0-wd01-part1-specification.txt
index 66d3bab..b7af1f9 100644
--- a/virtio-v1.0-wd01-part1-specification.txt
+++ b/virtio-v1.0-wd01-part1-specification.txt
@@ -67,6 +67,10 @@ Driver
 
 [RFC 2119] S. Bradner, Key words for use in RFCs to Indicate Requirement Levels, http://www.ietf.org/rfc/rfc2119.txt IETF (Internet Engineering Task Force) RFC 2119, March 1997.
 
+[S390 PoP] z/Architecture Principles of Operation, IBM Publication SA22-7832
+
+[S390 Common I/O] ESA/390 Common I/O-Device and Self-Description, IBM Publication SA22-7204
+
 1.3. Non-Normative References
 =========================
 
@@ -1581,6 +1585,23 @@ virtio:
 #define CCW_CMD_WRITE_STATUS 0x31
 #define CCW_CMD_READ_VQ_CONF 0x32
 
+The virtio-ccw device acts like a normal channel device, as specified
+in [S390 PoP] and [S390 Common I/O]. In particular:
+
+- A device must post a unit check with command reject for any command
+  it does not support.
+
+- If a driver did not suppress length checks for a channel command,
+  the device must present a subchannel status as detailed in the
+  architecture when the actual length did not match the expected length.
+
+- If a driver did suppress length checks for a channel command, the
+  device must present a check condition if the transmitted data does
+  not contain enough data to process the command. If the driver submitted
+  a buffer that was too long, the device should accept the command.
+  The driver should attempt to provide the correct length even if it
+  suppresses length checks.
+
 2.3.3.2. Device Initialization
 ------------------------------
 
-- 
1.7.9.5