mei: docs: add a short description for nfc behind mei

Signed-off-by: Tomas Winkler <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/driver-api/mei/index.rst

···
         Table of Contents
 
 .. toctree::
-   :maxdepth: 2
+   :maxdepth: 3
 
    mei
    mei-client-bus

Documentation/driver-api/mei/mei-client-bus.rst

···
 
         }
 
+MEI Client Bus Drivers
+======================
+
+.. toctree::
+   :maxdepth: 2
+
+   nfc

Documentation/driver-api/mei/nfc.rst

···
+.. SPDX-License-Identifier: GPL-2.0
+
+MEI NFC
+-------
+
+Some Intel 8 and 9 Serieses chipsets supports NFC devices connected behind
+the Intel Management Engine controller.
+MEI client bus exposes the NFC chips as NFC phy devices and enables
+binding with Microread and NXP PN544 NFC device driver from the Linux NFC
+subsystem.
+
+.. kernel-render:: DOT
+   :alt: MEI NFC digraph
+   :caption: **MEI NFC** Stack
+
+   digraph NFC {
+    cl_nfc -> me_cl_nfc;
+    "drivers/nfc/mei_phy" -> cl_nfc [lhead=bus];
+    "drivers/nfc/microread/mei" -> cl_nfc;
+    "drivers/nfc/microread/mei" -> "drivers/nfc/mei_phy";
+    "drivers/nfc/pn544/mei" -> cl_nfc;
+    "drivers/nfc/pn544/mei" -> "drivers/nfc/mei_phy";
+    "net/nfc" -> "drivers/nfc/microread/mei";
+    "net/nfc" -> "drivers/nfc/pn544/mei";
+    "neard" -> "net/nfc";
+    cl_nfc [label="mei/bus(nfc)"];
+    me_cl_nfc [label="me fw (nfc)"];
+   }