vas: Create MMIO device tree node

Create a device tree node for VAS and add properties that Linux
will need to configure/use VAS.

Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>

1 files changed, 28 insertions, 0 deletions

diff --git a/doc/device-tree/vas.rst b/doc/device-tree/vas.rst
new file mode 100644
index 0000000..606f476
--- /dev/null
+++ b/doc/device-tree/vas.rst
@@ -0,0 +1,28 @@
+Virtual Accelerator Switchboard (VAS)
+====================================
+
+VAS is present in P9 or later processors. In P9, each chip has one
+instance of VAS. Each instance of VAS is represented as a "platform
+device" i.e as a node in root of the device tree:
+::
+
+  /vas@<vas_addr>
+
+with unique VAS address which also represents the Hypervisor window
+context address for the instance of VAS.
+
+Each VAS node contains: ::
+
+  compatible: "ibm,power9-vas", "ibm,vas"
+  
+  ibm,vas-id: unique identifier for each instance of VAS in the system.
+
+  reg: contains 8 64-bit fields. 
+
+        Fields [0] and [1] represent the Hypervisor window context BAR
+        (start and length). Fields [2] and [3] represent the OS/User
+        window context BAR (start and length). Fields [4] and [5]
+        contain the start and length of paste power bus address region
+        for this chip. Fields [6] and [7] represent the bit field (start
+        bit and number of bits) where the window id of the window should
+        be encoded when computing the paste address for the window.