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Documentation is now handled by the same processes we use for code: Add something to the Documentation/ directory in the coreboot repo, and it will be rendered to https://doc.coreboot.org/. Contributions welcome!
- 1 Toward a unified representation for the layout of coreboot flash images
- 1.1 How it's currently done (how the Chromium OS project presently constructs firmware images)
- 1.2 What's so bad about that (the pitfalls of this build model that we hope to solve)
- 1.3 Why you should care (how this pertains to all coreboot users)
- 1.4 How do we fix it (the solution being pursued)
Toward a unified representation for the layout of coreboot flash images
N.B. The changes described herein are being made as part of the Chromium OS project; as such, they will initially be committed to the project's own fork of the main coreboot repository, which is available at https://chromium.googlesource.com/chromiumos/third_party/coreboot. Unless otherwise noted, the paths and processes described throughout this page are as they exist(ed) in a checkout of the master branch of the Chromium OS sources as they appeared at the beginning of 2015. One of the guiding design principles is to keep the tools general enough that they will be helpful to others, and the resulting work will be upstreamed to the main repository once it has been regression-tested in the context of Chromium OS hardware.
How it's currently done (how the Chromium OS project presently constructs firmware images)
Most Intel-based Chromium OS devices currently use an 8 MB firmware image that includes---among other things---the Intel ME firmware, a copy of coreboot including the ramstage and bootloader payload, two additional copies of the ramstage and bootloader payload, and a separate SeaBIOS payload. The primary description of this format exists in board-specific flattened device tree files. For instance, the layout of the Panther board's firmware exists at https://chromium.googlesource.com/chromiumos/platform/depthcharge/+/master/board/panther/fmap.dts, and results in an image that looks like this:
|0x700000||Boot (coreboot image)|
|0x611000||GBB (Google Binary Block)|
|0x610800||FWID (Firmware ID)|
|0x610000||FMAP (Flash MAP)|
|0x600000||RO-VPD (Vital Product Data)|
|0x400000||Legacy (SeaBIOS image)|
|0x3f8000||RW-VPD (Vital Product Data)|
|0x3f6000||Vblock-dev (third-party kernel signing keys)|
|0x3f4000||Shared-data (RW firmware calibration data)|
|0x3f0000||ELOG (Event LOG)|
|0x3e0000||MRC-cache (Memory Reference Code training data)|
What's so bad about that (the pitfalls of this build model that we hope to solve)
Why you should care (how this pertains to all coreboot users)
How do we fix it (the solution being pursued)
Integration into the coreboot build-system
Something similar to what we do for CBFS files
cbfs-regions-y += fw_readonly fw_readonly-name := GOD_SAVE_THE_FIRMWARE fw_readonly-offset := 0xblablabla fw-readonly-size := 0xblablabla
Put cbfs files in some default partition unless otherwise specified
# This is going into wherever the "default" cbfs partition is cbfs-files-y += spd.bin spd.bin-file := $(SPD_BIN) spd.bin-type := 0xab
Now if we wanted to explicitly put a file in some non-default region, we could do something like
cbfs-files-y += payloadizer payloadizer-region := USER_CAN_DO_WHATEVER payloadizer-file := payload_to_the_people payloadizer-type := blablabla
The advantage of having the notion of a default region means we can integrate the regionizing without disturbing existing code, which may not care about flash regions.