x86: Update README.x86 for coreboot support
Update README.x86 to include new build instructions for U-Boot as
the coreboot payload and testing considerations with coreboot.
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/README.x86 b/doc/README.x86
index b474161..7df8cc5 100644
--- a/doc/README.x86
+++ b/doc/README.x86
@@ -32,6 +32,21 @@
$ make coreboot-x86_defconfig
$ make all
+Note this default configuration will build a U-Boot payload for the Link board.
+To build a coreboot payload against another board, you can change the build
+configuration during the 'make menuconfig' process.
+
+x86 architecture --->
+ ...
+ (chromebook_link) Board configuration file
+ (chromebook_link) Board Device Tree Source (dts) file
+ (0x19200000) Board specific Cache-As-RAM (CAR) address
+ (0x4000) Board specific Cache-As-RAM (CAR) size
+
+Change the 'Board configuration file' and 'Board Device Tree Source (dts) file'
+to point to a new board. You can also change the Cache-As-RAM (CAR) related
+settings here if the default values do not fit your new board.
+
Building ROM version of U-Boot (hereafter referred to as u-boot.rom) is a
little bit tricky, as generally it requires several binary blobs which are not
shipped in the U-Boot source tree. Due to this reason, the u-boot.rom build is
@@ -88,11 +103,31 @@
Rename the first one to fsp.bin and second one to cmc.bin and put them in the
board directory.
-Now you can build U-Boot and obtaim u-boot.rom
+Now you can build U-Boot and obtain u-boot.rom
$ make crownbay_defconfig
$ make all
+Test with coreboot
+------------------
+For testing U-Boot as the coreboot payload, there are things that need be paid
+attention to. coreboot supports loading an ELF executable and a 32-bit plain
+binary, as well as other supported payloads. With the default configuration,
+U-Boot is set up to use a separate Device Tree Blob (dtb). As of today, the
+generated u-boot-dtb.bin needs to be packaged by the cbfstool utility (a tool
+provided by coreboot) manually as coreboot's 'make menuconfig' does not provide
+this capability yet. The command is as follows:
+
+# in the coreboot root directory
+$ ./build/util/cbfstool/cbfstool build/coreboot.rom add-flat-binary \
+ -f u-boot-dtb.bin -n fallback/payload -c lzma -l 0x1110000 -e 0x1110015
+
+Make sure 0x1110000 matches CONFIG_SYS_TEXT_BASE and 0x1110015 matches the
+symbol address of _start (in arch/x86/cpu/start.S).
+
+If you want to use ELF as the coreboot payload, change U-Boot configuration to
+use CONFIG_OF_EMBED.
+
CPU Microcode
-------------
Modern CPU usually requires a special bit stream called microcode [5] to be
@@ -106,7 +141,7 @@
Device Tree
-----------
x86 uses device tree to configure the board thus requires CONFIG_OF_CONTROL to
-be turned on. Not every device on the board is configured via devie tree, but
+be turned on. Not every device on the board is configured via device tree, but
more and more devices will be added as time goes by. Check out the directory
arch/x86/dts/ for these device tree source files.