xref: /openbmc/u-boot/doc/README.chromium (revision eee45b4f)
1Running U-Boot from coreboot on Chromebooks
2===========================================
3
4U-Boot can be used as a secondary boot loader in a few situations such as from
5UEFI and coreboot (see README.x86). Recent Chromebooks use coreboot even on
6ARM platforms to start up the machine.
7
8This document aims to provide a guide to booting U-Boot on a Chromebook. It
9is only a starting point, and there are many guides on the interwebs. But
10placing this information in the U-Boot tree should make it easier to find for
11those who use U-Boot habitually.
12
13Most of these platforms are supported by U-Boot natively, but it is risky to
14replace the ROM unless you have a servo board and cable to restore it with.
15
16
17For all of these the standard U-Boot build instructions apply. For example on
18ARM:
19
20   sudo apt install gcc-arm-linux-gnueabi
21   mkdir b
22   make O=b/nyan_big CROSS_COMPILE=arm-linux-gnueabi- nyan-big_defconfig all
23
24You can obtain the vbutil_kernel utility here:
25
26   https://drive.google.com/open?id=0B7WYZbZ9zd-3dHlVVXo4VXE2T0U
27
28
29Snow (Samsung ARM Chromebook)
30-----------------------------
31
32See here:
33
34https://www.chromium.org/chromium-os/firmware-porting-guide/using-nv-u-boot-on-the-samsung-arm-chromebook
35
36
37Nyan-big
38--------
39
40Compiled based on information here:
41https://lists.denx.de/pipermail/u-boot/2015-March/209530.html
42https://git.collabora.com/cgit/user/tomeu/u-boot.git/commit/?h=nyan-big
43https://lists.denx.de/pipermail/u-boot/2017-May/289491.html
44https://github.com/chromeos-nvidia-androidtv/gnu-linux-on-acer-chromebook-13#copy-data-to-the-sd-card
45
461. Build U-Boot
47
48   mkdir b
49   make -j8 O=b/nyan-big CROSS_COMPILE=arm-linux-gnueabi- nyan-big_defconfig all
50
51
522. Select a .its file
53
54Select something from doc/chromium which matches your board, or create your
55own.
56
57Note that the device tree node is required, even though it is not actually
58used by U-Boot. This is because the Chromebook expects to pass it to the
59kernel, and crashes if it is not present.
60
61
623. Build and sign an image
63
64   ./b/nyan-big/tools/mkimage -f doc/chromium/nyan-big.its u-boot-chromium.fit
65   echo test >dummy.txt
66   vbutil_kernel --arch arm --keyblock doc/chromium/devkeys/kernel.keyblock \
67	--signprivate doc/chromium/devkeys/kernel_data_key.vbprivk \
68	--version 1 --config dummy.txt --vmlinuz u-boot-chromium.fit \
69	--bootloader dummy.txt --pack u-boot.kpart
70
71
724. Prepare an SD card
73
74   DISK=/dev/sdc   # Replace with your actual SD card device
75   sudo cgpt create $DISK
76   sudo cgpt add -b 34 -s 32768 -P 1 -S 1 -t kernel $DISK
77   sudo cgpt add -b 32802 -s 2000000 -t rootfs $DISK
78   sudo gdisk $DISK   # Enter command 'w' to write a protective MBR to the disk
79
80
815. Write U-Boot to the SD card
82
83   sudo dd if=u-boot.kpart of=/dev/sdc1; sync
84
85
866. Start it up
87
88Reboot the device in dev mode. Make sure that you have USB booting enabled. To
89do this, login as root (via Ctrl-Alt-forward_arrow) and type
90'enable_dev_usb_boot'. You only need to do this once.
91
92Reboot the device with the SD card inserted. Press Clrl-U at the developer
93mode screen. It should show something like the following on the display:
94
95   U-Boot 2017.07-00637-g242eb42-dirty (May 22 2017 - 06:14:21 -0600)
96
97   Model: Acer Chromebook 13 CB5-311
98   Board: Google/NVIDIA Nyan-big, ID: 1
99
100   Net:   No ethernet found.
101   Hit any key to stop autoboot:  0
102   Tegra124 (Nyan-big) #
103
104
1057. Known problems
106
107On the serial console the word MMC is chopped at the start of the line:
108
109C:   sdhci@700b0000: 2, sdhci@700b0400: 1, sdhci@700b0600: 0
110
111This is likely due to some problem with change-over of the serial driver
112during relocation (or perhaps updating the clock setup in board_init()).
113
114
1159. Notes
116
117To check that you copied the u-boot.its file correctly, use these commands.
118You should see that the data at 0x100 in u-boot-chromium.fit is the first few
119bytes of U-Boot:
120
121   hd u-boot-chromium.fit |head -20
122   ...
123   00000100  b8 00 00 ea 14 f0 9f e5  14 f0 9f e5 14 f0 9f e5  |................|
124
125   hd b/nyan-big/u-boot.bin |head
126   00000000  b8 00 00 ea 14 f0 9f e5  14 f0 9f e5 14 f0 9f e5  |................|
127
128
129The 'data' property of the FIT is set up to start at offset 0x100 bytes into
130the file. The change to CONFIG_SYS_TEXT_BASE is also an offset of 0x100 bytes
131from the load address. If this changes, you either need to modify U-Boot to be
132fully relocatable, or expect it to hang.
133
134
135chromebook_jerry
136----------------
137
138The instruction are similar to those for Nyan with changes as noted below:
139
1401. Patch U-Boot
141
142Open include/configs/rk3288_common.h
143
144Change:
145
146#define CONFIG_SYS_TEXT_BASE		0x00100000
147
148to:
149
150#define CONFIG_SYS_TEXT_BASE		0x02000100
151
152
153
1542. Build U-Boot
155
156   mkdir b
157   make -j8 O=b/chromebook_jerry CROSS_COMPILE=arm-linux-gnueabi- \
158	chromebook_jerry_defconfig all
159
160
1613. See above
162
1634. Build and sign an image
164
165   ./b/chromebook_jerry/tools/mkimage -f doc/chromium/chromebook_jerry.its \
166	u-boot-chromium.fit
167   echo test >dummy.txt
168   vbutil_kernel --arch arm --keyblock doc/chromium/devkeys/kernel.keyblock \
169	--signprivate doc/chromium/devkeys/kernel_data_key.vbprivk \
170	--version 1 --config dummy.txt --vmlinuz u-boot-chromium.fit \
171	--bootloader dummy.txt --pack u-boot.kpart
172
173
1745. See above
175
1766. See above
177
1787. Start it up
179
180Reboot the device in dev mode. Make sure that you have USB booting enabled. To
181do this, login as root (via Ctrl-Alt-forward_arrow) and type
182'enable_dev_usb_boot'. You only need to do this once.
183
184Reboot the device with the SD card inserted. Press Clrl-U at the developer
185mode screen. It should show something like the following on the display:
186
187   U-Boot 2017.05-00649-g72acdbf-dirty (May 29 2017 - 14:57:05 -0600)
188
189   Model: Google Jerry
190   Net:   Net Initialization Skipped
191   No ethernet found.
192   Hit any key to stop autoboot:  0
193
194
1958. Known problems
196
197None as yet.
198
199
2009. Notes
201
202None as yet.
203
204
205Other notes
206===========
207
208flashrom
209--------
210
211   Used to make a backup of your firmware, or to replace it.
212
213   See: https://www.chromium.org/chromium-os/packages/cros-flashrom
214
215
216coreboot
217--------
218
219Coreboot itself is not designed to actually boot an OS. Instead, a program
220called Depthcharge is used. This originally came out of U-Boot and was then
221heavily hacked and modified such that is is almost unrecognisable. It does
222include a very small part of the U-Boot command-line interface but is not
223usable as a general-purpose boot loader.
224
225In addition, it has a very unusual design in that it does not do device init
226itself, but instead relies on coreboot. This is similar to (in U-Boot) having
227a SPI driver with an empty probe() method, relying on whatever was set up
228beforehand. It can be quite hard to figure out between these two code bases
229what settings are actually used. When chain-loading into U-Boot we must be
230careful to reinit anything that U-Boot expects. If not, some peripherals (or
231the whole machine) may not work. This makes the process of chainloading more
232complicated than it could be on some platforms.
233
234Finally, it supports only a subset of the U-Boot's FIT format. In particular
235it uses a fixed address to load the FIT and does not support load/exec
236addresses. This means that U-Boot must be able to boot from whatever
237address Depthcharge happens to use (it is the CONFIG_KERNEL_START setting
238in Depthcharge). In practice this means that the data in the kernel@1 FIT node
239(see above) must start at the same address as U-Boot's CONFIG_SYS_TEXT_BASE.
240