Nicholas Chin 35599f9a66 Docs: Replace Recommonmark with MyST Parser

Recommonmark has been deprecated since 2021 [1] and the last release was
over 3 years ago [2]. As per their announcement, Markedly Structured
Text (MyST) Parser [3] is the recommended replacement.

For the most part, the existing documentation is compatible with MyST,
as both parsers are built around the CommonMark flavor of Markdown. The
main difference that affects coreboot is how the Sphinx toctree is
generated. Recommonmark has a feature called auto_toc_tree, which
converts single level lists of references into a toctree:

* [Part 1: Starting from scratch](part1.md)
* [Part 2: Submitting a patch to coreboot.org](part2.md)
* [Part 3: Writing unit tests](part3.md)
* [Managing local additions](managing_local_additions.md)
* [Flashing firmware](flashing_firmware/index.md)

MyST Parser does not provide a replacement for this feature, meaning the
toctree must be defined manually. This is done using MyST's syntax for
Sphinx directives:

```{toctree}
:maxdepth: 1

Part 1: Starting from scratch <part1.md>
Part 2: Submitting a patch to coreboot.org <part2.md>
Part 3: Writing unit tests <part3.md>
Managing local additions <managing_local_additions.md>
Flashing firmware <flashing_firmware/index.md>
```

Internally, auto_toc_tree essentially converts lists of references into
the Sphinx toctree structure that the MyST syntax above more directly
represents.

The toctrees were converted to the MyST syntax using the following
command and Python script:

`find ./ -iname "*.md" | xargs -n 1 python conv_toctree.py`

```
import re
import sys

in_list = False
f = open(sys.argv[1])
lines = f.readlines()
f.close()

with open(sys.argv[1], "w") as f:
    for line in lines:
        match = re.match(r"^[-*+] \[(.*)\]\((.*)\)$", line)
        if match is not None:
            if not in_list:
                in_list = True
                f.write("```{toctree}\n")
                f.write(":maxdepth: 1\n\n")
            f.write(match.group(1) + " <" + match.group(2) + ">\n")
        else:
            if in_list:
                f.write("```\n")
            f.write(line)
            in_list = False

    if in_list:
        f.write("```\n")
```

While this does add a little more work for creating the toctree, this
does give more control over exactly what goes into the toctree. For
instance, lists of links to external resources currently end up in the
toctree, but we may want to limit it to pages within coreboot.

This change does break rendering and navigation of the documentation in
applications that can render Markdown, such as Okular, Gitiles, or the
GitHub mirror. Assuming the docs are mainly intended to be viewed after
being rendered to doc.coreboot.org, this is probably not an issue in
practice.

Another difference is that MyST natively supports Markdown tables,
whereas with Recommonmark, tables had to be written in embedded rST [4].
However, MyST also supports embedded rST, so the existing tables can be
easily converted as the syntax is nearly identical.

These were converted using
`find ./ -iname "*.md" | xargs -n 1 sed -i "s/eval_rst/{eval-rst}/"`

Makefile.sphinx and conf.py were regenerated from scratch by running
`sphinx-quickstart` using the updated version of Sphinx, which removes a
lot of old commented out boilerplate. Any relevant changes coreboot had
made on top of the previous autogenerated versions of these files were
ported over to the newly generated file.

From some initial testing the generated webpages appear and function
identically to the existing documentation built with Recommonmark.

TEST: `make -C util/docker docker-build-docs` builds the documentation
successfully and the generated output renders properly when viewed in
a web browser.

[1] https://github.com/readthedocs/recommonmark/issues/221
[2] https://pypi.org/project/recommonmark/
[3] https://myst-parser.readthedocs.io/en/latest/
[4] https://doc.coreboot.org/getting_started/writing_documentation.html

Change-Id: I0837c1722fa56d25c9441ea218e943d8f3d9b804
Signed-off-by: Nicholas Chin <nic.c3.14@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/73158
Reviewed-by: Matt DeVillier <matt.devillier@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

2024-03-21 16:11:56 +00:00

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SMM based flash storage driver

This documents the API exposed by the x86 system management based storage driver.

SMMSTORE

SMMSTORE is a SMM mediated driver to read from, write to and erase a predefined region in flash. It can be enabled by setting CONFIG_SMMSTORE=y in menuconfig.

This can be used by the OS or the payload to implement persistent storage to hold for instance configuration data, without needing to implement a (platform specific) storage driver in the payload itself.

The API provides append-only semantics for key/value pairs.

API

Storage region

By default SMMSTORE will operate on a separate FMAP region called SMMSTORE. The default generated FMAP will include such a region. On systems with a locked FMAP, e.g. in an existing vboot setup with a locked RO region, the option exists to add a cbfsfile called smm_store in the RW_LEGACY (if CHROMEOS) or in the COREBOOT FMAP regions. It is recommended for new builds using a handcrafted FMD that intend to make use of SMMSTORE to include a sufficiently large SMMSTORE FMAP region. It is recommended to align the SMMSTORE region to 64KiB for the largest flash erase op compatibility.

When a default generated FMAP is used the size of the FMAP region is equal to CONFIG_SMMSTORE_SIZE. UEFI payloads expect at least 64KiB. Given that the current implementation lacks a way to rewrite key-value pairs at least a multiple of this is recommended.

generating the SMI

SMMSTORE is called via an SMI, which is generated via a write to the IO port defined in the smi_cmd entry of the FADT ACPI table. %al contains APM_CNT_SMMSTORE=0xed and is written to the smi_cmd IO port. %ah contains the SMMSTORE command. %ebx contains the parameter buffer to the SMMSTORE command.

Return values

If a command succeeds, SMMSTORE will return with SMMSTORE_RET_SUCCESS=0 on %eax. On failure SMMSTORE will return SMMSTORE_RET_FAILURE=1. For unsupported SMMSTORE commands SMMSTORE_REG_UNSUPPORTED=2 is returned.

NOTE1: The caller must check the return value and should make no assumption on the returned data if %eax does not contain SMMSTORE_RET_SUCCESS.

NOTE2: If the SMI returns without changing %ax assume that the SMMSTORE feature is not installed.

Calling arguments

SMMSTORE supports 3 subcommands that are passed via %ah, the additional calling arguments are passed via %ebx.

NOTE: The size of the struct entries are in the native word size of smihandler. This means 32 bits in almost all cases.

- SMMSTORE_CMD_CLEAR = 1

This clears the SMMSTORE storage region. The argument in %ebx is unused.

- SMMSTORE_CMD_READ = 2

The additional parameter buffer %ebx contains a pointer to the following struct:

struct smmstore_params_read {
	void *buf;
	ssize_t bufsize;
};

INPUT:

buf: is a pointer to where the data needs to be read
bufsize: is the size of the buffer

OUTPUT:

buf
bufsize: returns the amount of data that has actually been read.

- SMMSTORE_CMD_APPEND = 3

SMMSTORE takes a key-value approach to appending data. key-value pairs are never updated, they are always appended. It is up to the caller to walk through the key-value pairs after reading SMMSTORE to find the latest one.