[PATCH v2] docs/arm64: update the documention for loading XSM support

[fu.wei@linaro.org]

From: Fu Wei <fu.wei@linaro.org>

This patch updates the documentation for allowing detection of an XSM
module that lacks a specific compatible string.
This mechanism has been added by the commit
ca32012341f3de7d3975407fb963e6028f0d0c8b.

Signed-off-by: Fu Wei <fu.wei@linaro.org>
---
v2: Improve the doc, according to the suggestion from Julien Grall.

v1: http://lists.xen.org/archives/html/xen-devel/2016-04/msg02070.html
    The first upstream version submitted in xen-devel mailing list.

 docs/misc/arm/device-tree/booting.txt | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/docs/misc/arm/device-tree/booting.txt b/docs/misc/arm/device-tree/booting.txt
index ad98bf3..254ba77 100644
--- a/docs/misc/arm/device-tree/booting.txt
+++ b/docs/misc/arm/device-tree/booting.txt
@@ -24,10 +24,24 @@ Each node contains the following properties:
 	string (which must always be present).
 
 	Xen will assume that the first module which lacks a more
-	specific compatible string is a "multiboot,kernel" and that
-	the second such is a "multiboot,ramdisk". Any subsequent
-	modules which lack a specific compatiblity string will not
-	receive any special treatment.
+	specific compatible string is a "multiboot,kernel".
+
+	Xen will check all the modules for the XSM Magic from the second
+	module that lacks a specific compatible string. According to the
+	result of the detection:
+	- if it's a XSM, Xen will assume its compatible string is a
+	  "xen,xsm-policy";
+	- if it's not a XSM, for the second module that lacks a specific
+	  compatible string, Xen will assume its compatible string is a
+	  "multiboot,ramdisk"; for the third and subsequent modules those
+	  lacks a specific compatible string will not receive any special
+	  treatment.
+	This means if the ramdisk module is present and does not have the
+	compatible string "multiboot,ramdisk", then it must always be the
+	second module.
+	Note: This XSM Magic detection behavior was introduced by Xen 4.7.
+	Xen 4.6 (and downwards) still requires the XSM module to have the
+	compatible string "xen,xsm-policy".
 
 	Xen 4.4 supported a different set of legacy compatible strings
 	which remain supported such that systems supporting both 4.4
-- 
2.5.5


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