[PATCH v3 5/5] docs: Update s390 vfio-ap doc for ap_config sysfs attribute

["Jason J. Herne" <jjherne@linux.ibm.com>]

A new sysfs attribute, ap_config, for the vfio_ap driver is
documented.

Signed-off-by: Jason J. Herne <jjherne@linux.ibm.com>
---
 Documentation/arch/s390/vfio-ap.rst | 30 +++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/Documentation/arch/s390/vfio-ap.rst b/Documentation/arch/s390/vfio-ap.rst
index 929ee1c1c940..6056a50ee841 100644
--- a/Documentation/arch/s390/vfio-ap.rst
+++ b/Documentation/arch/s390/vfio-ap.rst
@@ -380,6 +380,36 @@ matrix device.
     control_domains:
       A read-only file for displaying the control domain numbers assigned to the
       vfio_ap mediated device.
+    ap_config:
+        A read/write file that, when written to, allows all three of the
+        vfio_ap mediated device's ap matrix masks to be replaced in one shot.
+        Three masks are given, one for adapters, one for domains, and one for
+        control domains. If the given state cannot be set then no changes are
+        made to the vfio-ap mediated device.
+
+        The format of the data written to ap_config is as follows:
+        {amask},{dmask},{cmask}\n
+
+        \n is a newline character.
+
+        amask, dmask, and cmask are masks identifying which adapters, domains,
+        and control domains should be assigned to the mediated device.
+
+        The format of a mask is as follows:
+        0xNN..NN
+
+        Where NN..NN is 64 hexadecimal characters representing a 256-bit value.
+        The leftmost (highest order) bit represents adapter/domain 0.
+
+        For an example set of masks that represent your mdev's current
+        configuration, simply cat ap_config.
+
+        Setting an adapter or domain number greater than the maximum allowed for
+        the system will result in an error.
+
+        This attribute is intended to be used by automation. End users would be
+        better served using the respective assign/unassign attributes for
+        adapters, domains, and control domains.
 
 * functions:
 
-- 
2.41.0