[PATCH v3 7/7] xen/docs: Describe static shared memory when host address is not provided

[Luca Fancellu <luca.fancellu@xxxxxxx>]

From: Penny Zheng <Penny.Zheng@xxxxxxx>

This commit describe the new scenario where host address is not provided
in "xen,shared-mem" property and a new example is added to the page to
explain in details.

Take the occasion to fix some typos in the page.

Signed-off-by: Penny Zheng <penny.zheng@xxxxxxx>
Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>
Reviewed-by: Michal Orzel <michal.orzel@xxxxxxx>
---
v2:
 - Add Michal R-by
v1:
 - patch from 
https://patchwork.kernel.org/project/xen-devel/patch/20231206090623.1932275-10-Penny.Zheng@xxxxxxx/
   with some changes in the commit message.
---
 docs/misc/arm/device-tree/booting.txt | 52 ++++++++++++++++++++-------
 1 file changed, 39 insertions(+), 13 deletions(-)

diff --git a/docs/misc/arm/device-tree/booting.txt 
b/docs/misc/arm/device-tree/booting.txt
index bbd955e9c2f6..ac4bad6fe5e0 100644
--- a/docs/misc/arm/device-tree/booting.txt
+++ b/docs/misc/arm/device-tree/booting.txt
@@ -590,7 +590,7 @@ communication.
     An array takes a physical address, which is the base address of the
     shared memory region in host physical address space, a size, and a guest
     physical address, as the target address of the mapping.
-    e.g. xen,shared-mem = < [host physical address] [guest address] [size] >
+    e.g. xen,shared-mem = < [host physical address] [guest address] [size] >;
 
     It shall also meet the following criteria:
     1) If the SHM ID matches with an existing region, the address range of the
@@ -601,8 +601,8 @@ communication.
     The number of cells for the host address (and size) is the same as the
     guest pseudo-physical address and they are inherited from the parent node.
 
-    Host physical address is optional, when missing Xen decides the location
-    (currently unimplemented).
+    Host physical address is optional, when missing Xen decides the location.
+    e.g. xen,shared-mem = < [guest address] [size] >;
 
 - role (Optional)
 
@@ -629,7 +629,7 @@ chosen {
         role = "owner";
         xen,shm-id = "my-shared-mem-0";
         xen,shared-mem = <0x10000000 0x10000000 0x10000000>;
-    }
+    };
 
     domU1 {
         compatible = "xen,domain";
@@ -640,25 +640,36 @@ chosen {
         vpl011;
 
         /*
-         * shared memory region identified as 0x0(xen,shm-id = <0x0>)
-         * is shared between Dom0 and DomU1.
+         * shared memory region "my-shared-mem-0" is shared
+         * between Dom0 and DomU1.
          */
         domU1-shared-mem@10000000 {
             compatible = "xen,domain-shared-memory-v1";
             role = "borrower";
             xen,shm-id = "my-shared-mem-0";
             xen,shared-mem = <0x10000000 0x50000000 0x10000000>;
-        }
+        };
 
         /*
-         * shared memory region identified as 0x1(xen,shm-id = <0x1>)
-         * is shared between DomU1 and DomU2.
+         * shared memory region "my-shared-mem-1" is shared between
+         * DomU1 and DomU2.
          */
         domU1-shared-mem@50000000 {
             compatible = "xen,domain-shared-memory-v1";
             xen,shm-id = "my-shared-mem-1";
             xen,shared-mem = <0x50000000 0x60000000 0x20000000>;
-        }
+        };
+
+        /*
+         * shared memory region "my-shared-mem-2" is shared between
+         * DomU1 and DomU2.
+         */
+        domU1-shared-mem-2 {
+            compatible = "xen,domain-shared-memory-v1";
+            xen,shm-id = "my-shared-mem-2";
+            role = "owner";
+            xen,shared-mem = <0x80000000 0x20000000>;
+        };
 
         ......
 
@@ -672,14 +683,21 @@ chosen {
         cpus = <1>;
 
         /*
-         * shared memory region identified as 0x1(xen,shm-id = <0x1>)
-         * is shared between domU1 and domU2.
+         * shared memory region "my-shared-mem-1" is shared between
+         * domU1 and domU2.
          */
         domU2-shared-mem@50000000 {
             compatible = "xen,domain-shared-memory-v1";
             xen,shm-id = "my-shared-mem-1";
             xen,shared-mem = <0x50000000 0x70000000 0x20000000>;
-        }
+        };
+
+        domU2-shared-mem-2 {
+            compatible = "xen,domain-shared-memory-v1";
+            xen,shm-id = "my-shared-mem-2";
+            role = "borrower";
+            xen,shared-mem = <0x90000000 0x20000000>;
+        };
 
         ......
     };
@@ -699,3 +717,11 @@ shared between DomU1 and DomU2. It will get mapped at 
0x60000000 in DomU1 guest
 physical address space, and at 0x70000000 in DomU2 guest physical address 
space.
 DomU1 and DomU2 are both the borrower domain, the owner domain is the default
 owner domain DOMID_IO.
+
+For the static shared memory region "my-shared-mem-2", since host physical
+address is not provided by user, Xen will automatically allocate 512MB
+from heap as static shared memory to be shared between DomU1 and DomU2.
+The automatically allocated static shared memory will get mapped at
+0x80000000 in DomU1 guest physical address space, and at 0x90000000 in DomU2
+guest physical address space. DomU1 is explicitly defined as the owner domain,
+and DomU2 is the borrower domain.
-- 
2.34.1