[Xen-devel] [PATCH v2] xen: arm: doc: Add firmware requirements

[Dirk Behme <dirk.behme@xxxxxxxxxxxx>]

Add a section about what the firmware should do in EL3 before starting Xen.

E.g. on ARM Linux the HVC instruction is used to trap into Xen. As this
can be set only at EL3, i.e. outside from Xen, document this boot requirement.

Signed-off-by: Dirk Behme <dirk.behme@xxxxxxxxxxxx>
---
 docs/misc/arm/booting.txt | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/docs/misc/arm/booting.txt b/docs/misc/arm/booting.txt
index 9802e5e..b0ff305 100644
--- a/docs/misc/arm/booting.txt
+++ b/docs/misc/arm/booting.txt
@@ -23,6 +23,21 @@ The exceptions to this on 32-bit ARM are as follows:
 
 There are no exception on 64-bit ARM.
 
+
+Firmware/bootloader requirements
+--------------------------------
+
+Xen relies on some settings the firmware has to do in EL3 before starting
+Xen.
+
+* EL2: Xen must be entered in NS EL2 mode
+
+* HCE: It has to be ensured that the Secure Configuration Register
+       has the HVC instructions enabled at EL1 and above
+       ARM32: SCR.HCE == 1
+       ARM64: SCR_EL3.HCE == 1
+
+
 [1] linux/Documentation/arm/Booting
 Latest version: 
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/arm/Booting
 
-- 
2.8.0


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