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diff --git a/Documentation/soc/intel/fit.md b/Documentation/soc/intel/fit.md new file mode 100644 index 0000000000..8b638f0433 --- /dev/null +++ b/Documentation/soc/intel/fit.md @@ -0,0 +1,60 @@ +# Intel Firmware Interface Table + +The FIT allows to run code before the actual IA32 reset vector is executed +by the CPU. The FIT resides in the BIOS region (usually near the reset vector) +and is pointed to by the FIT pointer residing at `0xFFFFFFC0`. + +## Table layout +The table consists of blocks each 16 bytes in size. +The first is called *FIT header* the other are called *FIT entry*. + +![FIT in x86 memory map][fit] + +[fit]: fit.svg + +## Fit types + +Each entry has a *type* that give the other bits in the entry a different +meaning. The following types are known: + +```eval_rst ++-----------+------------------------------------------------------------------+ +| no. | Description | ++===========+==================================================================+ +| 0x0 | HEADER. | ++-----------+------------------------------------------------------------------+ +| 0x1 | MICROCODE. | ++-----------+------------------------------------------------------------------+ +| 0x2 | STARTUP_ACM. | ++-----------+------------------------------------------------------------------+ +| 0x7 | BIOS_STARTUP_MODULE. | ++-----------+------------------------------------------------------------------+ +| 0x8 | TPM_POLICY. | ++-----------+------------------------------------------------------------------+ +| 0x9 | BIOS_POLICY. | ++-----------+------------------------------------------------------------------+ +| 0xa | TXT_POLICY. | ++-----------+------------------------------------------------------------------+ +| 0xb | KEY_MANIFEST. | ++-----------+------------------------------------------------------------------+ +| 0xc | BOOT_POLICY_MANIFEST. | ++-----------+------------------------------------------------------------------+ +| 0x10 | CSE_SECURE_BOOT. | ++-----------+------------------------------------------------------------------+ +| 0x2d | TXTSX_POLICY. | ++-----------+------------------------------------------------------------------+ +| 0x2f | JMP_DEBUG_POLICY. | ++-----------+------------------------------------------------------------------+ +| 0x7f | SKIP. | ++-----------+------------------------------------------------------------------+ +``` + +## Usage in coreboot + +The most common usage of FIT is to use *Type1* to update microcode before +execution of the IA32 reset vector happens. + +## References + +* [Intel TXT LAB handout](https://downloadmirror.intel.com/18931/eng/Intel%20TXT%20LAB%20Handout.pdf) +* [FIT bios specification](https://www.intel.com/content/dam/www/public/us/en/documents/guides/fit-bios-specification.pdf) |