Change in ...coreboot[master]: Documentation: Convert cbfs.txt to markdown

[Patrick Rudolph (Code Review)]

Patrick Rudolph has uploaded this change for review. ( https://review.coreboot.org/c/coreboot/+/33663

Change subject: Documentation: Convert cbfs.txt to markdown
......................................................................

Documentation: Convert cbfs.txt to markdown

Convert the document to markdown.
Needs to be fixed in a separate commit as it doesn't reflect coreboot v4.

Change-Id: I0fb2713a9cda08e528902ec641dd4a4e0dc148fe
Signed-off-by: Patrick Rudolph 
---
A Documentation/lib/cbfs.md
M Documentation/lib/index.md
2 files changed, 372 insertions(+), 0 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/63/33663/1

diff --git a/Documentation/lib/cbfs.md b/Documentation/lib/cbfs.md
new file mode 100644
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--- /dev/null
+++ b/Documentation/lib/cbfs.md
@@ -0,0 +1,371 @@
+# coreboot CBFS Specification
+by Jordan Crouse 
+
+**WARNING: This documentation is written against coreboot v1.**
+
+**TODO: Update this document ASAP**
+
+## Introduction
+
+This document describes the coreboot CBFS specification (from here
+referred to as CBFS). CBFS is a scheme for managing independent chunks
+of data in a system ROM. Though not a true filesystem, the style and
+concepts are similar.
+
+
+## Architecture
+
+The CBFS architecture looks like the following:
+
+```
+/---------------\ <-- Start of ROM
+| /-----------\ | --|
+| | Header    | |   |
+| |-----------| |   |
+| | Name      | |   |-- Component
+| |-----------| |   |
+| |Data       | |   |
+| |..         | |   |
+| -----------/ | --|
+|               |
+| /-----------\ |
+| | Header    | |
+| |-----------| |
+| | Name      | |
+| |-----------| |
+| |Data       | |
+| |..         | |
+| -----------/ |
+|               |
+| ...           |
+| /-----------\ |
+| |           | |
+| | Bootblock | |
+| | --------- | |
+| | Reset     | | <- 0xFFFFFFF0
+| -----------/ |
+---------------/
+```
+
+The CBFS architecture consists of a binary associated with a physical
+ROM disk referred hereafter as the ROM. A number of independent of
+components, each with a  header prepended on to data are located within
+the ROM.  The components are nominally arranged sequentially, though they
+are aligned along a pre-defined boundary.
+
+The bootblock occupies the last 20k of the ROM.  Within
+the bootblock is a master header containing information about the ROM
+including the size, alignment of the components, and the offset of the
+start of the first CBFS component within the ROM.
+
+## Master Header
+
+The master header contains essential information about the ROM that is
+used by both the CBFS implementation within coreboot at runtime as well
+as host based utilities to create and manage the ROM.  The master header
+will be located somewhere within the bootblock (last 20k of the ROM).  A
+pointer to the location of the header will be located at offset
+-4 from the end of the ROM.  This translates to address 0xFFFFFFFC on a
+normal x86 system.  The pointer will be to physical memory somewhere
+between - 0xFFFFB000 and 0xFFFFFFF0.  This makes it easier for coreboot
+to locate the header at run time.  Build time utilities will
+need to read the pointer and do the appropriate math to locate the header.
+
+The following is the structure of the master header:
+
+```c
+struct cbfs_header {
+        u32 magic;
+        u32 version;
+        u32 romsize;
+        u32 bootblocksize;
+        u32 align;
+        u32 offset;
+        u32 architecture;
+        u32 pad[1];
+} __packed;
+```
+
+The meaning of each member is as follows:
+
+`magic` is a 32 bit number that identifies the ROM as a CBFS type.  The
+magic
+number is 0x4F524243, which is 'ORBC' in ASCII.
+
+`version` is a version number for CBFS header. cbfs_header structure may be
+different if version is not matched.
+
+`romsize` is the size of the ROM in bytes.  coreboot will subtract 'size' from
+0xFFFFFFFF to locate the beginning of the ROM in memory.
+
+`bootblocksize` is the size of bootblock reserved in firmware image.
+
+`align` is the number of bytes that each component is aligned to within the
+ROM.  This is used to make sure that each component is aligned correctly
+with
+regards to the erase block sizes on the ROM - allowing one to replace a
+component at runtime without disturbing the others.
+
+`offset` is the offset of the first CBFS component (from the start of
+the ROM).  This is to allow for arbitrary space to be left at the beginning
+of the ROM for things like embedded controller firmware.
+
+`architecture` describes which architecture (x86, arm, ...) this CBFS is created
+for.
+
+## Bootblock
+The bootblock is a mandatory component in the ROM.  It is located in the
+last 20k of the ROM space, and contains, among other things, the location of the
+master header and the entry point for the loader firmware.  The bootblock
+does not have a component header attached to it.
+
+## Components
+
+CBFS components are placed in the ROM starting at 'offset' specified in
+the master header and ending at the bootblock.  Thus the total size
+available for components in the ROM is (ROM size - 20k - 'offset').
+Each CBFS component is to be aligned according to the 'align' value in the
+header.
+Thus, if a component of size 1052 is located at offset 0 with an 'align'
+value of 1024, the next component will be located at offset 2048.
+
+Each CBFS component will be indexed with a unique ASCII string name of
+unlimited size.
+
+Each CBFS component starts with a header:
+
+```c
+struct cbfs_file {
+         char magic[8];
+         unsigned int len;
+         unsigned int type;
+         unsigned int checksum;
+         unsigned int offset;
+};
+```
+
+`magic` is a magic value used to identify the header.  During runtime,
+coreboot will scan the ROM looking for this value.  The default magic is
+the string 'LARCHIVE'.
+
+`len` is the length of the data, not including the size of the header and
+the size of the name.
+
+`type` is a 32 bit number indicating the type of data that is attached.
+The data type is used in a number of ways, as detailed in the section
+below.
+
+`checksum` is a 32bit checksum of the entire component, including the
+header and name.
+
+`offset` is the start of the component data, based off the start of the
+header.
+The difference between the size of the header and offset is the size of the
+component name.
+
+Immediately following the header will be the name of the component,
+which will null terminated and 16 byte aligned. The following picture shows the
+structure of the header:
+
+```
+/--------\  <- start
+| Header |
+|--------|  <- sizeof(struct cbfs_file)
+| Name   |
+|--------|  <- 'offset'
+| Data   |
+| ...    |
+--------/  <- start + 'offset' + 'len'
+```
+
+### Searching Algorithm
+
+To locate a specific component in the ROM, one starts at the 'offset'
+specified in the CBFS master header.  For this example, the offset will
+be 0.
+
+From that offset, the code should search for the magic string on the
+component, jumping 'align' bytes each time.  So, assuming that 'align' is
+16, the code will search for the string 'LARCHIVE' at offset 0, 16, 32, etc.
+If the offset ever exceeds the allowable range for CBFS components, then no
+component was found.
+
+Upon recognizing a component, the software then has to search for the
+specific name of the component.  This is accomplished by comparing the
+desired name with the string on the component located at
+`offset + sizeof(struct cbfs_file)`.  If the string matches, then the
+component has been located, otherwise the software should add
+`'offset' + 'len'` to the offset and resume the search for the magic value.
+
+### Data Types
+
+The 'type' member of struct cbfs_file is used to identify the content
+of the component data, and is used by coreboot and other
+run-time entities to make decisions about how to handle the data.
+
+There are three component types that are essential to coreboot, and so
+are defined here.
+
+#### Stages
+
+Stages are code loaded by coreboot during the boot process.  They are
+essential to a successful boot.   Stages are comprised of a single blob
+of binary data that is to be loaded into a particular location in memory
+and executed.   The uncompressed header contains information about how
+large the data is, and where it should be placed, and what additional memory
+needs to be cleared.
+
+Stages are assigned a component value of 0x10.  When coreboot sees this
+component type, it knows that it should pass the data to a sub-function
+that will process the stage.
+
+The following is the format of a stage component:
+
+```
+/--------\
+| Header |
+|--------|
+| Binary |
+| ..     |
+--------/
+```
+
+The header is defined as:
+
+```c
+struct cbfs_stage {
+         unsigned int compression;
+         unsigned long long entry;
+         unsigned long long load;
+         unsigned int len;
+         unsigned int memlen;
+};
+```
+
+`compression` is an integer defining how the data is compressed.  There
+are three compression types defined by this version of the standard:
+none (0x0), lzma (0x1), and nrv2b (0x02, deprecated), though additional
+types may be added assuming that coreboot understands how to handle the scheme.
+
+`entry` is a 64 bit value indicating the location where  the program
+counter should jump following the loading of the stage. This should be
+an absolute physical memory address.
+
+`load` is a 64 bit value indicating where the subsequent data should be
+loaded. This should be an absolute physical memory address.
+
+`len` is the length of the compressed data in the component.
+
+`memlen` is the amount of memory that will be used by the component when
+it is loaded.
+
+The component data will start immediately following the header.
+
+When coreboot loads a stage, it will first zero the memory from 'load' to
+'memlen'.  It will then decompress the component data according to the
+specified scheme and place it in memory starting at 'load'.  Following that,
+it will jump execution to the address specified by 'entry'.
+Some components are designed to execute directly from the ROM - coreboot
+knows which components must do that and will act accordingly.
+
+#### Payloads
+
+Payloads are loaded by coreboot following the boot process.
+
+Stages are assigned a component value of 0x20.  When coreboot sees this
+component type, it knows that it should pass the data to a sub-function
+that will process the payload.  Furthermore, other run time applications such
+as 'bayou' may easily index all available payloads
+on the system by searching for the payload type.
+
+
+The following is the format of a stage component:
+
+```
+/-----------\
+| Header    |
+| Segment 1 |
+| Segment 2 |
+| ...       |
+|-----------|
+| Binary    |
+| ..        |
+-----------/
+```
+
+The header is as follows:
+
+```c
+struct cbfs_payload {
+         struct cbfs_payload_segment segments;
+}
+```
+
+The header contains a number of segments corresponding to the segments
+that need to be loaded for the payload.
+
+The following is the structure of each segment header:
+
+```c
+struct cbfs_payload_segment {
+         unsigned int type;
+         unsigned int compression;
+         unsigned int offset;
+         unsigned long long load_addr;
+         unsigned int len;
+         unsigned int mem_len;
+};
+```
+
+`type` is the type of segment, one of the following:
+
+```eval_rst
++----------------------+-------------+---------------------------------------+
+|PAYLOAD_SEGMENT_CODE  |  0x45444F43 | The segment contains executable code  |
++----------------------+-------------+---------------------------------------+
+|PAYLOAD_SEGMENT_DATA  |  0x41544144 | The segment contains data             |
++----------------------+-------------+---------------------------------------+
+|PAYLOAD_SEGMENT_BSS   |  0x20535342 | The memory specified by the segment   |
+|                      |             | should be zeroed                      |
++----------------------+-------------+---------------------------------------+
+|PAYLOAD_SEGMENT_PARAMS|  0x41524150 | The segment contains information for  |
+|                      |             | the payload                           |
++----------------------+-------------+---------------------------------------+
+|PAYLOAD_SEGMENT_ENTRY |  0x52544E45 | The segment contains the entry point  |
+|                      |             | for the payload                       |
++----------------------+-------------+---------------------------------------+
+```
+
+`compression` is the compression scheme for the segment.  Each segment can
+be independently compressed. There are three compression types defined by
+this version of the standard: none (0x0), lzma (0x1), and nrv2b
+(0x02, deprecated), though additional types may be added assuming that
+coreboot understands how to handle the scheme.
+
+`offset` is the address of the data within the component, starting from
+the component header.
+
+`load_addr` is a 64 bit value indicating where the segment should be placed
+in memory.
+
+`len` is a 32 bit value indicating the size of the segment within the
+component.
+
+`mem_len` is the size of the data when it is placed into memory.
+
+The data will located immediately following the last segment.
+
+#### Option ROMS
+
+The third specified component type will be Option ROMs.  Option ROMS will
+have component type '0x30'.  They will have no additional header, the
+uncompressed binary data will be located in the data portion of the
+component.
+
+#### NULL
+
+There is a 4th component type ,defined as NULL (0xFFFFFFFF).  This is
+the "don't care" component type.  This can be used when the component
+type is not necessary (such as when the name of the component is unique.
+i.e. option_table).  It is recommended that all components be assigned a
+unique type, but NULL can be used when the type does not matter.
diff --git a/Documentation/lib/index.md b/Documentation/lib/index.md
index 99b8061..808bac8 100644
--- a/Documentation/lib/index.md
+++ b/Documentation/lib/index.md
@@ -6,4 +6,5 @@
 ## Structure and layout
 - [Flashmap and Flashmap Descriptor](flashmap.md)
 - [ABI data consumption](abi-data-consumption.md)
+- [CBFS](cbfs.md)
 - [Timestamps](timestamp.md)

[Paul Menzel (Code Review)]

Paul Menzel has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/33663 )

Change subject: Documentation: Convert cbfs.txt to markdown
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Patch Set 2: Code-Review+1

Change in coreboot[master]: Documentation: Convert cbfs.txt to markdown

[Krystian Hebel (Code Review)]

Krystian Hebel has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/33663 )

Change subject: Documentation: Convert cbfs.txt to markdown
......................................................................

Patch Set 2: Code-Review+1

Change in coreboot[master]: Documentation: Convert cbfs.txt to markdown

[Alexey Vazhnov (Code Review)]

Attention is currently required from: Patrick Rudolph.
Alexey Vazhnov has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/33663 )

Change subject: Documentation: Convert cbfs.txt to markdown
......................................................................

Patch Set 2: Code-Review+1

[L] Change in coreboot[master]: Documentation: Convert cbfs.txt to markdown

[Martin L Roth (Code Review)]

Martin L Roth has abandoned this change. ( https://review.coreboot.org/c/coreboot/+/33663?usp=email )

Change subject: Documentation: Convert cbfs.txt to markdown
......................................................................

Abandoned

This patch has not been touched in over 12 months. Anyone who wants to take over work on this patch, please feel free to restore it and do any work needed to get it merged. If you create a new patch based on this work, please credit the original author.