x86: Add device tree support

[cascardo/linux.git] / Documentation / devicetree / booting-without-of.txt

diff --git a/Documentation/devicetree/booting-without-of.txt b/Documentation/devicetree/booting-without-of.txt
index 28b1c9d..55fd262 100644 (file)
--- a/Documentation/devicetree/booting-without-of.txt
+++ b/Documentation/devicetree/booting-without-of.txt
@@ -13,6 +13,7 @@ Table of Contents
 
   I - Introduction
     1) Entry point for arch/powerpc
+    2) Entry point for arch/x86
 
   II - The DT block format
     1) Header
@@ -225,6 +226,25 @@ it with special cases.
   cannot support both configurations with Book E and configurations
   with classic Powerpc architectures.
 
+2) Entry point for arch/x86
+-------------------------------
+
+  There is one single 32bit entry point to the kernel at code32_start,
+  the decompressor (the real mode entry point goes to the same  32bit
+  entry point once it switched into protected mode). That entry point
+  supports one calling convention which is documented in
+  Documentation/x86/boot.txt
+  The physical pointer to the device-tree block (defined in chapter II)
+  is passed via setup_data which requires at least boot protocol 2.09.
+  The type filed is defined as
+
+  #define SETUP_DTB                      2
+
+  This device-tree is used as an extension to the "boot page". As such it
+  does not parse / consider data which is already covered by the boot
+  page. This includes memory size, reserved ranges, command line arguments
+  or initrd address. It simply holds information which can not be retrieved
+  otherwise like interrupt routing or a list of devices behind an I2C bus.
 
 II - The DT block format
 ========================