docs/arm64: update the documentation for loading XSM support

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>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>
Acked-by: Julien Grall <julien.grall@arm.com>
Release-acked-by: Wei Liu <wei.liu2@citrix.com>

diff --git a/docs/misc/arm/device-tree/booting.txt b/docs/misc/arm/device-tree/booting.txt
index ad98bf3cd156a12bdb8ad27cacdd364acd68ef34..cae46edaa2ffe62fd9df0ff8b5f415e5cc1bcec2 100644 (file)
--- 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 an XSM, Xen will assume its compatible string is
+         "xen,xsm-policy";
+       - if it's not an XSM, for the second module that lacks a specific
+         compatible string, Xen will assume its compatible string is
+         "multiboot,ramdisk"; the third and subsequent modules that
+         lack a specific compatible string will not receive any special
+         treatment.
+       This means that 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