[PATCH] docs/design: boot domain device tree design

["Daniel P. Smith" <dpsmith@xxxxxxxxxxxxxxxxxxxx>]

This is a Request For Comments on the adoption of Device Tree as the
format for the Launch Control Module as described in the previously
posted DomB RFC.

For RFC purposes, a rendered of this file can be found here:
https://drive.google.com/file/d/1FUv3U-KSB0H2X2tmBdv5Lt-6_BJm4nF1/view?usp=sharing

Details on the DomB boot domain can be found on Xen wiki:
https://wiki.xenproject.org/wiki/DomB_mode_of_dom0less

Signed-off-by: Daniel P. Smith <dpsmith@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Christopher Clark <christopher.clark@xxxxxxxxxx>
---
 docs/designs/boot-domain-device-tree.rst | 163 +++++++++++++++++++++++++++++++
 1 file changed, 163 insertions(+)
 create mode 100644 docs/designs/boot-domain-device-tree.rst

diff --git a/docs/designs/boot-domain-device-tree.rst 
b/docs/designs/boot-domain-device-tree.rst
new file mode 100644
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--- /dev/null
+++ b/docs/designs/boot-domain-device-tree.rst
@@ -0,0 +1,163 @@
+====================================
+Xen Boot Domain Device Tree Bindings
+====================================
+
+The Xen Boot Domain device tree adopts the dom0less device tree structure and
+extends it to meet the requirements for the Boot Domain capability. The primary
+difference is the introduction of the ``xen`` node that is under the 
``/chosen``
+node. The move to a dedicated node was driven by:
+
+1. Reduces the need to walk over nodes that are not of interest, e.g.  only
+nodes of interest should be in ``/chosen/xen``
+
+2. Enables the use of the ``#address-cells`` and ``#size-cells`` fields on the
+xen node.
+
+Below is an example device tree definition for a xen node followed by an
+explanation of each section and field:
+::
+    xen {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        // Boot Domain definition
+        domain@0 {
+            #address-cells = <1>;
+            #size-cells = <0>;
+            compatible = "xen,domain";
+
+            reg = <0x7FF5>;
+            memory = <0x0 0x20000>;
+            cpus = <1>;
+            module@0 {
+                compatible = "multiboot,kernel", "multiboot,module";
+                reg = <1>;
+            };
+
+            module@1 {
+                compatible = "multiboot,ramdisk", "multiboot,module";
+                reg = <2>;
+            };
+            module@3 {
+                compatible = "multiboot,config", "multiboot,module";
+                reg = <3>;
+            };
+
+        // Classic Dom0 definition
+        domain@1 {
+            #address-cells = <1>;
+            #size-cells = <0>;
+
+            reg = <0>;
+
+            // PERMISSION_NONE          (0)
+            // PERMISSION_CONTROL       (1 << 0)
+            // PERMISSION_HARDWARE      (1 << 1)
+            permissions = <3>;
+
+            // FUNCTION_NONE            (0)
+            // FUNCTION_BOOT            (1 << 1)
+            // FUNCTION_CRASH           (1 << 2)
+            // FUNCTION_CONSOLE         (1 << 3)
+            // FUNCTION_XENSTORE        (1 << 30)
+            // FUNCTION_LEGACY_DOM0     (1 << 31)
+            functions = <0xFFFFFFFF>;
+
+            // MODE_PARAVIRTUALIZED     (1 << 0) /* PV | PVH/HVM */
+            // MODE_ENABLE_DEVICE_MODEL (1 << 1) /* PVH | HVM */
+            mode = <1>;
+
+            // UUID
+            domain-handle = [B3 FB 98 FB 8F 9F 67 A3 8A 6E 62 5A 09 13 F0 8C];
+
+            cpus = <1>;
+            memory = <0x0 0x20000>;
+            security-id = <0>;
+
+            module@0 {
+                compatible = "multiboot,kernel", "multiboot,module";
+                reg = <4>;
+                bootargs = "console=hv0";
+            };
+            module@1 {
+                compatible = "multiboot,ramdisk", "multiboot,module";
+                reg = <5>;
+            };
+    };
+
+The Xen node
+------------
+
+The xen node is a top level container for the domains that will be built by
+hypervisor on start up. On the ``xen`` node the ``#address-cells`` is set to 
one
+and the ``#size-cells`` is set to zero. This is done to enforce that each 
domain
+node must define a ``reg`` property and the hypervisor will use it to determine
+the ``domid`` for the domain.
+
+The Domain node
+----------------
+
+A domain node is for describing the construction of a domain. It is free to set
+the ``#address-cells`` and ``#size-cells`` depending on how the multiboot
+modules identified and located. If the multiboot modules will be located by
+index within the module chain, the values should be “1” and “0” respectively. 
If
+the multiboot module will be located by address, then the values should be “1”
+and “1” respectively.
+
+As previously mentioned a domain node must have a reg property which will be
+used as the requested domain id for the domain with a value of “0” signifying 
to
+use the next available domain id. After that a domain node may have any of the
+following parameters,
+
+reg
+  Identifies the domid to use for the domain. Required.
+
+permissions
+  This sets what Discretionary Access Control permissions a domain is assigned.
+  Optional, default is none.
+
+functions
+  This identifies what system functions a domain will fulfill.  Optional, the
+  default is none.
+
+.. note::  The last two ``functions`` bits are used for ``FUNCTION_XENSTORE`` 
and ``FUNCTION_LEGACY_DOM0`` such that should these features ever be fully 
retired, the flags may be dropped without leaving a gap in the flag set.
+
+mode
+  The mode the domain will be executed under. Required.
+
+domain-handle
+  A globally unique identifier for the domain. Optional, the default is NULL.
+
+cpus
+  The number of vCPUs to be assigned to the domain. Optional, the default is
+  “1”.
+
+memory
+  The amount of memory to assign to the domain, in KBs. Required.
+
+security-id
+  The security identity to be assigned to the domain when XSM is the access
+  control mechanism being used. Optional, the default is “domu”.
+
+The Module node
+---------------
+
+This node describes a multiboot module loaded by the boot loader. The required
+``compatible`` property follows the format: ``multiboot, <type>`` where type 
can
+be “module”, “kernel”, “ramdisk”, “memory-map”, lcm, or “config”. The ``reg``
+property is required and identifies how to locate the multiboot module.
+
+compatible
+  This identifies what the module is and thus what the hypervisor should use 
the
+  module for during domain construction. Required.
+
+reg
+  This identifies where this module is located within the multiboot module
+  chain. Required.
+
+bootargs
+  This is used to override the boot params carried in multiboot module.
+  Optional.
+
+.. note::  The bootargs property is intended for situations where the same 
kernel multiboot module is used for more than one domain.
+
-- 
2.11.0