66 lines
2.3 KiB
Markdown
66 lines
2.3 KiB
Markdown
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# IFD Layout
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A coreboot image for an Intel SoC contains two separate definitions of the
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layout of the flash. The Intel Flash Descriptor (IFD) which defines offsets and
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sizes of various regions of flash and the [coreboot FMAP](../lib/flashmap.md).
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The FMAP should define all of the of the regions defined by the IFD to ensure
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that those regions are accounted for by coreboot and will not be accidentally
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modified.
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## IFD mapping
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The names of the IFD regions in the FMAP should follow the convention of
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starting with the prefix `SI_` which stands for `silicon initialization` as a
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way to categorize anything required by the SoC but not provided by coreboot.
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|IFD Region index|IFD Region name|FMAP Name|Notes|
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|---|---|---|---|
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|0|Flash Descriptor|SI_DESC|Always the top 4KB of flash|
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|1|BIOS|SI_BIOS|This is the region that contains coreboot|
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|2|Intel ME|SI_ME||
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|3|Gigabit Ethernet|SI_GBE||
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|4|Platform Data|SI_PDR||
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|8|EC Firmware|SI_EC|Most Chrome OS devices do not use this region; EC firmware is stored BIOS region of flash|
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## Validation
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The ifdtool can be used to manipulate a firmware image with a IFD. This tool
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will not take into account the FMAP while modifying the image which can lead to
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unexpected and hard to debug issues with the firmware image. For example if the
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ME region is defined at 6 MB in the IFD but the FMAP only allocates 4 MB for the
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ME, then when the ME is added by the ifdtool 6 MB will be written which could
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overwrite 2 MB of the BIOS.
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In order to validate that the FMAP and the IFD are compatible the ifdtool
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provides --validate (-t) option. `ifdtool -t` will read both the IFD and the
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FMAP in the image and for every non empty region in the IFD if that region is
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defined in the FMAP but the offset or size is different then the tool will
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return an error.
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Example:
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```console
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foo@bar:~$ ifdtool -t bad_image.bin
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Region mismatch between bios and SI_BIOS
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Descriptor region bios:
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offset: 0x00400000
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length: 0x01c00000
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FMAP area SI_BIOS:
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offset: 0x00800000
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length: 0x01800000
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Region mismatch between me and SI_ME
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Descriptor region me:
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offset: 0x00103000
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length: 0x002f9000
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FMAP area SI_ME:
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offset: 0x00103000
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length: 0x006f9000
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Region mismatch between pd and SI_PDR
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Descriptor region pd:
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offset: 0x003fc000
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length: 0x00004000
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FMAP area SI_PDR:
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offset: 0x007fc000
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length: 0x00004000
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```
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