[PULL v2 5/6] vfio-ccw: Update documentation for csch/hsch

[Cornelia Huck <cohuck@redhat.com>]

From: Farhan Ali <alifm@linux.ibm.com>

We now support CLEAR SUBCHANNEL and HALT SUBCHANNEL
via ccw_cmd_region.

Fixes: d5afd5d135c8 ("vfio-ccw: add handling for async channel instructions")
Signed-off-by: Farhan Ali <alifm@linux.ibm.com>
Message-Id: <7d977612c3f3152ffb950d77ae11b4b25c1e20c4.1562854091.git.alifm@linux.ibm.com>
[CH: properly mark region as literal block]
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Eric Farman <farman@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
---
 Documentation/s390/vfio-ccw.rst | 31 ++++++++++++++++++++++++++++---
 1 file changed, 28 insertions(+), 3 deletions(-)

diff --git a/Documentation/s390/vfio-ccw.rst b/Documentation/s390/vfio-ccw.rst
index 1f6d0b56d53e..be2af10e12b4 100644
--- a/Documentation/s390/vfio-ccw.rst
+++ b/Documentation/s390/vfio-ccw.rst
@@ -180,6 +180,13 @@ The process of how these work together.
    add it to an iommu_group and a vfio_group. Then we could pass through
    the mdev to a guest.
 
+
+VFIO-CCW Regions
+----------------
+
+The vfio-ccw driver exposes MMIO regions to accept requests from and return
+results to userspace.
+
 vfio-ccw I/O region
 -------------------
 
@@ -205,6 +212,25 @@ irb_area stores the I/O result.
 
 ret_code stores a return code for each access of the region.
 
+This region is always available.
+
+vfio-ccw cmd region
+-------------------
+
+The vfio-ccw cmd region is used to accept asynchronous instructions
+from userspace.
+
+#define VFIO_CCW_ASYNC_CMD_HSCH (1 << 0)
+#define VFIO_CCW_ASYNC_CMD_CSCH (1 << 1)
+struct ccw_cmd_region {
+       __u32 command;
+       __u32 ret_code;
+} __packed;
+
+This region is exposed via region type VFIO_REGION_SUBTYPE_CCW_ASYNC_CMD.
+
+Currently, CLEAR SUBCHANNEL and HALT SUBCHANNEL use this region.
+
 vfio-ccw operation details
 --------------------------
 
@@ -306,9 +332,8 @@ Together with the corresponding work in QEMU, we can bring the passed
 through DASD/ECKD device online in a guest now and use it as a block
 device.
 
-While the current code allows the guest to start channel programs via
-START SUBCHANNEL, support for HALT SUBCHANNEL or CLEAR SUBCHANNEL is
-not yet implemented.
+The current code allows the guest to start channel programs via
+START SUBCHANNEL, and to issue HALT SUBCHANNEL and CLEAR SUBCHANNEL.
 
 vfio-ccw supports classic (command mode) channel I/O only. Transport
 mode (HPF) is not supported.
-- 
2.20.1