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c9af6673 SG |
1 | Running U-Boot from coreboot on Chromebooks |
2 | =========================================== | |
3 | ||
4 | U-Boot can be used as a secondary boot loader in a few situations such as from | |
5 | UEFI and coreboot (see README.x86). Recent Chromebooks use coreboot even on | |
6 | ARM platforms to start up the machine. | |
7 | ||
8 | This document aims to provide a guide to booting U-Boot on a Chromebook. It | |
9 | is only a starting point, and there are many guides on the interwebs. But | |
10 | placing this information in the U-Boot tree should make it easier to find for | |
11 | those who use U-Boot habitually. | |
12 | ||
13 | Most of these platforms are supported by U-Boot natively, but it is risky to | |
14 | replace the ROM unless you have a servo board and cable to restore it with. | |
15 | ||
16 | ||
17 | For all of these the standard U-Boot build instructions apply. For example on | |
18 | ARM: | |
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 | ||
24 | You can obtain the vbutil_kernel utility here: | |
25 | ||
26 | https://drive.google.com/open?id=0B7WYZbZ9zd-3dHlVVXo4VXE2T0U | |
27 | ||
28 | ||
29 | Snow (Samsung ARM Chromebook) | |
30 | ----------------------------- | |
31 | ||
32 | See here: | |
33 | ||
34 | https://www.chromium.org/chromium-os/firmware-porting-guide/using-nv-u-boot-on-the-samsung-arm-chromebook | |
35 | ||
36 | ||
37 | Nyan-big | |
38 | -------- | |
39 | ||
40 | Compiled based on information here: | |
41 | https://lists.denx.de/pipermail/u-boot/2015-March/209530.html | |
42 | https://git.collabora.com/cgit/user/tomeu/u-boot.git/commit/?h=nyan-big | |
43 | https://lists.denx.de/pipermail/u-boot/2017-May/289491.html | |
44 | https://github.com/chromeos-nvidia-androidtv/gnu-linux-on-acer-chromebook-13#copy-data-to-the-sd-card | |
45 | ||
46 | 1. Patch U-Boot | |
47 | ||
48 | Open include/configs/tegra124-common.h | |
49 | ||
50 | Change: | |
51 | ||
52 | #define CONFIG_SYS_TEXT_BASE 0x80110000 | |
53 | ||
54 | to: | |
55 | ||
56 | #define CONFIG_SYS_TEXT_BASE 0x81000100 | |
57 | ||
58 | ||
59 | 2. Build U-Boot | |
60 | ||
61 | mkdir b | |
62 | make -j8 O=b/nyan-big CROSS_COMPILE=arm-linux-gnueabi- nyan-big_defconfig all | |
63 | ||
64 | ||
65 | 3. Select a .its file | |
66 | ||
67 | Select something from doc/chromium which matches your board, or create your | |
68 | own. | |
69 | ||
70 | Note that the device tree node is required, even though it is not actually | |
71 | used by U-Boot. This is because the Chromebook expects to pass it to the | |
72 | kernel, and crashes if it is not present. | |
73 | ||
74 | ||
75 | 4. Build and sign an image | |
76 | ||
77 | ./b/nyan-big/tools/mkimage -f doc/chromium/nyan-big.its u-boot-chromium.fit | |
78 | echo test >dummy.txt | |
79 | vbutil_kernel --arch arm --keyblock doc/chromium/devkeys/kernel.keyblock \ | |
80 | --signprivate doc/chromium/devkeys/kernel_data_key.vbprivk \ | |
81 | --version 1 --config dummy.txt --vmlinuz u-boot-chromium.fit \ | |
82 | --bootloader dummy.txt --pack u-boot.kpart | |
83 | ||
84 | ||
85 | 5. Prepare an SD card | |
86 | ||
87 | DISK=/dev/sdc # Replace with your actual SD card device | |
88 | sudo cgpt create $DISK | |
89 | sudo cgpt add -b 34 -s 32768 -P 1 -S 1 -t kernel $DISK | |
90 | sudo cgpt add -b 32802 -s 2000000 -t rootfs $DISK | |
91 | sudo gdisk $DISK # Enter command 'w' to write a protective MBR to the disk | |
92 | ||
93 | ||
94 | 6. Write U-Boot to the SD card | |
95 | ||
96 | sudo dd if=u-boot.kpart of=/dev/sdc1; sync | |
97 | ||
98 | ||
99 | 7. Start it up | |
100 | ||
101 | Reboot the device in dev mode. Make sure that you have USB booting enabled. To | |
102 | do this, login as root (via Ctrl-Alt-forward_arrow) and type | |
103 | 'enable_dev_usb_boot'. You only need to do this once. | |
104 | ||
105 | Reboot the device with the SD card inserted. Press Clrl-U at the developer | |
106 | mode screen. It should show something like the following on the display: | |
107 | ||
108 | U-Boot 2017.07-00637-g242eb42-dirty (May 22 2017 - 06:14:21 -0600) | |
109 | ||
110 | Model: Acer Chromebook 13 CB5-311 | |
111 | Board: Google/NVIDIA Nyan-big, ID: 1 | |
112 | ||
113 | Net: No ethernet found. | |
114 | Hit any key to stop autoboot: 0 | |
115 | Tegra124 (Nyan-big) # | |
116 | ||
117 | ||
118 | 8. Known problems | |
119 | ||
120 | On the serial console the word MMC is chopped at the start of the line: | |
121 | ||
122 | C: sdhci@700b0000: 2, sdhci@700b0400: 1, sdhci@700b0600: 0 | |
123 | ||
124 | This is likely due to some problem with change-over of the serial driver | |
125 | during relocation (or perhaps updating the clock setup in board_init()). | |
126 | ||
127 | ||
128 | 9. Notes | |
129 | ||
130 | To check that you copied the u-boot.its file correctly, use these commands. | |
131 | You should see that the data at 0x100 in u-boot-chromium.fit is the first few | |
132 | bytes of U-Boot: | |
133 | ||
134 | hd u-boot-chromium.fit |head -20 | |
135 | ... | |
136 | 00000100 b8 00 00 ea 14 f0 9f e5 14 f0 9f e5 14 f0 9f e5 |................| | |
137 | ||
138 | hd b/nyan-big/u-boot.bin |head | |
139 | 00000000 b8 00 00 ea 14 f0 9f e5 14 f0 9f e5 14 f0 9f e5 |................| | |
140 | ||
141 | ||
142 | The 'data' property of the FIT is set up to start at offset 0x100 bytes into | |
143 | the file. The change to CONFIG_SYS_TEXT_BASE is also an offset of 0x100 bytes | |
144 | from the load address. If this changes, you either need to modify U-Boot to be | |
145 | fully relocatable, or expect it to hang. | |
146 | ||
147 | ||
fe67eacc SG |
148 | chromebook_jerry |
149 | ---------------- | |
150 | ||
151 | The instruction are similar to those for Nyan with changes as noted below: | |
152 | ||
153 | 1. Patch U-Boot | |
154 | ||
155 | Open include/configs/rk3288_common.h | |
156 | ||
157 | Change: | |
158 | ||
159 | #define CONFIG_SYS_TEXT_BASE 0x00100000 | |
160 | ||
161 | to: | |
162 | ||
163 | #define CONFIG_SYS_TEXT_BASE 0x02000100 | |
164 | ||
165 | ||
166 | ||
167 | 2. Build U-Boot | |
168 | ||
169 | mkdir b | |
170 | make -j8 O=b/chromebook_jerry CROSS_COMPILE=arm-linux-gnueabi- \ | |
171 | chromebook_jerry_defconfig all | |
172 | ||
173 | ||
174 | 3. See above | |
175 | ||
176 | 4. Build and sign an image | |
177 | ||
178 | ./b/chromebook_jerry/tools/mkimage -f doc/chromium/chromebook_jerry.its \ | |
179 | u-boot-chromium.fit | |
180 | echo test >dummy.txt | |
181 | vbutil_kernel --arch arm --keyblock doc/chromium/devkeys/kernel.keyblock \ | |
182 | --signprivate doc/chromium/devkeys/kernel_data_key.vbprivk \ | |
183 | --version 1 --config dummy.txt --vmlinuz u-boot-chromium.fit \ | |
184 | --bootloader dummy.txt --pack u-boot.kpart | |
185 | ||
186 | ||
187 | 5. See above | |
188 | ||
189 | 6. See above | |
190 | ||
191 | 7. Start it up | |
192 | ||
193 | Reboot the device in dev mode. Make sure that you have USB booting enabled. To | |
194 | do this, login as root (via Ctrl-Alt-forward_arrow) and type | |
195 | 'enable_dev_usb_boot'. You only need to do this once. | |
196 | ||
197 | Reboot the device with the SD card inserted. Press Clrl-U at the developer | |
198 | mode screen. It should show something like the following on the display: | |
199 | ||
200 | U-Boot 2017.05-00649-g72acdbf-dirty (May 29 2017 - 14:57:05 -0600) | |
201 | ||
202 | Model: Google Jerry | |
203 | Net: Net Initialization Skipped | |
204 | No ethernet found. | |
205 | Hit any key to stop autoboot: 0 | |
206 | ||
207 | ||
208 | 8. Known problems | |
209 | ||
210 | None as yet. | |
211 | ||
212 | ||
213 | 9. Notes | |
214 | ||
215 | None as yet. | |
216 | ||
217 | ||
c9af6673 SG |
218 | Other notes |
219 | =========== | |
220 | ||
221 | flashrom | |
222 | -------- | |
223 | ||
224 | Used to make a backup of your firmware, or to replace it. | |
225 | ||
226 | See: https://www.chromium.org/chromium-os/packages/cros-flashrom | |
227 | ||
228 | ||
229 | coreboot | |
230 | -------- | |
231 | ||
232 | Coreboot itself is not designed to actually boot an OS. Instead, a program | |
233 | called Depthcharge is used. This originally came out of U-Boot and was then | |
234 | heavily hacked and modified such that is is almost unrecognisable. It does | |
235 | include a very small part of the U-Boot command-line interface but is not | |
236 | usable as a general-purpose boot loader. | |
237 | ||
238 | In addition, it has a very unusual design in that it does not do device init | |
239 | itself, but instead relies on coreboot. This is similar to (in U-Boot) having | |
240 | a SPI driver with an empty probe() method, relying on whatever was set up | |
241 | beforehand. It can be quite hard to figure out between these two code bases | |
242 | what settings are actually used. When chain-loading into U-Boot we must be | |
243 | careful to reinit anything that U-Boot expects. If not, some peripherals (or | |
244 | the whole machine) may not work. This makes the process of chainloading more | |
245 | complicated than it could be on some platforms. | |
246 | ||
247 | Finally, it supports only a subset of the U-Boot's FIT format. In particular | |
248 | it uses a fixed address to load the FIT and does not support load/exec | |
249 | addresses. This means that U-Boot must be able to boot from whatever | |
250 | address Depthcharge happens to use (it is the CONFIG_KERNEL_START setting | |
251 | in Depthcharge). In practice this means that the data in the kernel@1 FIT node | |
252 | (see above) must start at the same address as U-Boot's CONFIG_SYS_TEXT_BASE. |