README.chromium 5.4 KB

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  1. Chromium OS Support in U-Boot
  2. =============================
  3. Introduction
  4. ------------
  5. This describes how to use U-Boot with Chromium OS. Several options are
  6. available:
  7. - Running U-Boot from the 'altfw' feature, which is available on selected
  8. Chromebooks from 2019 onwards (initially Grunt). Press '1' from the
  9. developer-mode screen to get into U-Boot. See here for details:
  10. https://sites.google.com/a/chromium.org/dev/chromium-os/poking-around-your-chrome-os-device?pli=1
  11. - Running U-Boot from the disk partition. This involves signing U-Boot and
  12. placing it on the disk, for booting as a 'kernel'. See
  13. README.chromium-chainload for information on this. This is the only
  14. option on non-U-Boot Chromebooks from 2013 to 2018 and is somewhat
  15. more involved.
  16. - Running U-Boot with Chromium OS verified boot. This allows U-Boot to be
  17. used instead of either or both of depthcharge (a bootloader which forked
  18. from U-Boot in 2013) and coreboot. See below for more information on
  19. this.
  20. U-Boot with Chromium OS verified boot
  21. -------------------------------------
  22. To obtain:
  23. git clone https://github.com/sglass68/u-boot.git
  24. cd u-boot
  25. git checkout cros-master
  26. To build for sandbox:
  27. UB=/tmp/b/chromeos_sandbox # U-Boot build directory
  28. CROS=/home/sglass/cosarm # Chromium OS directory
  29. make O=$UB/chromeos_sandbox_defconfig
  30. make O=$UB -j20 -s VBOOT_SOURCE=$CROS/src/platform/vboot_reference \
  31. MAKEFLAGS_VBOOT=DEBUG=1 QUIET=1
  32. Replace sandbox with another supported target.
  33. This produces $UB/image.bin which contains the firmware binaries in a SPI
  34. flash image.
  35. To run on sandbox:
  36. $UB/tpl/u-boot-tpl -d $UB/u-boot.dtb.out \
  37. -L6 -c "host bind 0 $CROS/src/build/images/cheza/latest/chromiumos_image.bin; vboot go auto" \
  38. -l -w -s state.dtb -r
  39. To run on other boards:
  40. Install image.bin in the SPI flash of your device
  41. Boot your system
  42. Sandbox
  43. -------
  44. Most Chromium OS development with U-Boot is undertaken using sandbox. There is
  45. a sandbox target available (chromeos_sandbox) which allows running U-Boot on
  46. a Linux machine completion with emulations of the display, TPM, disk, etc.
  47. Running sandbox starts TPL, which contains the first phase of vboot, providing
  48. a device tree and binding a Chromium OS disk image for use to find kernels
  49. (any Chromium OS image will do). It also saves driver state between U-Boot
  50. phases into state.dtb and will automatically ensure that memory is shared
  51. between all phases. TPL will jump to SPL and then on to U-Boot proper.
  52. It is possible to run with debugging on, e.g.
  53. gdb --args $UB/tpl/u-boot-tpl -d ....
  54. Breakpoints can be set in any U-Boot phase. Overall this is a good debugging
  55. environment for new verified-boot features.
  56. Samus
  57. -----
  58. Basic support is available for samus, using the chromeos_samus target. If you
  59. have an em100, use:
  60. sudo em100 -s -c W25Q128FW -d $UB/image.bin -t -r
  61. to write the image and then boot samus (Power-Refresh).
  62. Boot flow
  63. ---------
  64. Verified boot starts in TPL, which selects the A or B SPL, which in turn selects
  65. the A or B U-Boot. Then this jumps to the selected kernel. If anything goes
  66. wrong, the device reboots and the recovery SPL and U-Boot are used instead.
  67. More details are available here:
  68. https://www.chromium.org/chromium-os/chromiumos-design-docs/firmware-boot-and-recovery
  69. New uclasses
  70. ------------
  71. Several uclasses are provided in cros/:
  72. UCLASS_CROS_AUX_FW Chrome OS auxiliary firmware
  73. UCLASS_CROS_FWSTORE Chrome OS firmware storage
  74. UCLASS_CROS_NVDATA Chrome OS non-volatile data device
  75. UCLASS_CROS_VBOOT_EC Chrome OS vboot EC operations
  76. UCLASS_CROS_VBOOT_FLAG Chrome OS verified boot flag
  77. The existing UCLASS_CROS_EC is also used.
  78. Commands
  79. --------
  80. A new 'vboot' command is provided to run particular vboot stages. The most
  81. useful command is 'vboot go auto', which continues where the last stage left
  82. off.
  83. Note that TPL and SPL do not supports commands as yet, so the vboot code is
  84. called directly from the SPL boot devices (BOOT_DEVICE_CROS_VBOOT). See
  85. cros_load_image_tpl() and cros_load_image_spl() which both call
  86. vboot_run_auto().
  87. Config options
  88. --------------
  89. The main option is CONFIG_CHROMEOS, which enables a wide array of other options
  90. so that the required features are present.
  91. Device-tree config
  92. ------------------
  93. Various options are available which control the operation of verified boot.
  94. See cros/dts/bindings/config.txt for details. Most config is handled at run-
  95. time, although build-time config (with Kconfig) could also be added fairly
  96. easily.
  97. Porting to other hardware
  98. -------------------------
  99. A basic port to samus (Chromebook Pixel 2015) is in a basic working state,
  100. using the chromeos_samus target. Patches will likely be forthcoming in early
  101. 2019. Ports to an ARM board and coreboot (for x86 Chromebooks) are in the
  102. dreaming state.
  103. Tests
  104. -----
  105. Chromium OS firmware has a very limited set of tests. The tests that originally
  106. existed in U-Boot were not brought over to coreboot or depthcharge.
  107. The U-Boot tests ('make check') do operate, but at present there are no
  108. Chromium OS tests available. These will hopefully come together over time. Of
  109. course the above sandbox feature provides a sort of functional test and can
  110. detecte problems that affect the flow or particular vboot features.
  111. TO DO
  112. -----
  113. - Support for booting from coreboot (patches expected March 2019)
  114. - Support for booting from an ARM board, e.g. bob
  115. Simon Glass
  116. sjg@chromium.org
  117. 7 October 2018