Documentation/timestamp.md: Fix markdown formatting

Fix the headline levels (only the document's title should be a top-level
document), and use "# " instead of "====" to mark headlines, because
it's more obvious what the different levels of that are. Also fix some
other things.

Arguably, the explicit table of contents could be removed.

Change-Id: Ie29b6393e9d7871ea3c900e016b5c3ed415538ac
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Reviewed-on: https://review.coreboot.org/25680
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>
Reviewed-by: Furquan Shaikh <furquan@google.com>
This commit is contained in:
Jonathan Neuschäfer 2018-04-08 15:05:14 +02:00 committed by Patrick Georgi
parent 7719d50352
commit 0bb93707c8
1 changed files with 69 additions and 69 deletions

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@ -1,33 +1,31 @@
Table of Contents
=================
# Timestamps
## Table of Contents
Introduction
Transition from cache to cbmem
- Transition from cache to cbmem
Data structures used
cache_state
table
entries
- cache_state
- table
- entries
Function APIs
timestamp_init
timestamp_add
timestamp_add_now
timestamp_sync
- timestamp_init
- timestamp_add
- timestamp_add_now
- timestamp_sync
Use / Test Cases
Case 1: Timestamp Region Exists
Case 2: No timestamp region, fresh boot, cbmem_initialize called after
timestamp_init
Case 3: No timestamp region, fresh boot, cbmem_initialize called before
timestamp_init
Case 4: No timestamp region, resume, cbmem_initialize called after
timestamp_init
Case 5: No timestamp region, resume, cbmem_initialize called before
timestamp_init
- Case 1: Timestamp Region Exists
- Case 2: No timestamp region, fresh boot, cbmem_initialize called after timestamp_init
- Case 3: No timestamp region, fresh boot, cbmem_initialize called before timestamp_init
- Case 4: No timestamp region, resume, cbmem_initialize called after timestamp_init
- Case 5: No timestamp region, resume, cbmem_initialize called before timestamp_init
Introduction
============
## Introduction
The aim of the timestamp library is to make it easier for different boards
to save timestamps in cbmem / stash (until cbmem is brought up) by
providing a simple API to initialize, add and sync timestamps. In order
@ -51,8 +49,8 @@ Behind the scenes, the timestamp library takes care of:
3. Add a new cbmem timestamp area based on whether a reset of the cbmem
timestamp region is required or not.
Transition from cache to cbmem
------------------------------
### Transition from cache to cbmem
To move timestamps from the cache to cbmem (and initialize the cbmem area in
the first place), we use the CBMEM_INIT_HOOK infrastructure of coreboot.
@ -62,25 +60,30 @@ copies all timestamps to cbmem and disables the cache.
After such a transition, timestamp_init() must not be run again.
Data structures used
====================
## Data structures used
The main structure that maintains information about the timestamp cache is:
```
struct __packed timestamp_cache {
uint16_t cache_state;
struct timestamp_table table;
struct timestamp_entry entries[MAX_TIMESTAMP_CACHE];
};
```
cache_state
-----------
The state of the cache is maintained by cache_state attribute which can
### cache_state
The state of the cache is maintained by `cache_state` attribute which can
be any one of the following:
```
enum {
TIMESTAMP_CACHE_UNINITIALIZED = 0,
TIMESTAMP_CACHE_INITIALIZED,
TIMESTAMP_CACHE_NOT_NEEDED,
};
```
By default, if the cache is stored in local stash (bss area), then
it will be reset to uninitialized state. However, if the cache is
@ -89,112 +92,109 @@ attributes. Thus, if the timestamp region is being used by any board, it is
initialized to default values by the library.
Once the cache is initialized, its state is set to
CACHE_INITIALIZED. Henceforth, the calls to cache i.e. timestamp_add
`CACHE_INITIALIZED`. Henceforth, the calls to cache i.e. `timestamp_add`
know that the state reflected is valid and timestamps can be directly
saved in the cache.
Once the cbmem area is up (i.e. call to timestamp_sync_cache_to_cbmem),
Once the cbmem area is up (i.e. call to `timestamp_sync_cache_to_cbmem`),
we do not need to store the timestamps in local stash / timestamp area
anymore. Thus, the cache state is set to CACHE_NOT_NEEDED, which allows
timestamp_add to store all timestamps directly into the cbmem area.
anymore. Thus, the cache state is set to `CACHE_NOT_NEEDED`, which allows
`timestamp_add` to store all timestamps directly into the cbmem area.
table
-----
### table
This field is represented by a structure which provides overall
information about the entries in the timestamp area:
```
struct timestamp_table {
uint64_t base_time;
uint32_t max_entries;
uint32_t num_entries;
struct timestamp_entry entries[0]; /* Variable number of entries */
} __packed;
```
It indicates the base time for all timestamp entries, maximum number
of entries that can be stored, total number of entries that currently
exist and an entry structure to hold variable number of entries.
entries
-------
### entries
This field holds the details of each timestamp entry, upto a maximum
of MAX_TIMESTAMP_CACHE which is defined as 16 entries. Each entry is
of `MAX_TIMESTAMP_CACHE` which is defined as 16 entries. Each entry is
defined by:
```
struct timestamp_entry {
uint32_t entry_id;
uint64_t entry_stamp;
} __packed;
```
entry_id holds the timestamp id corresponding to this entry and
entry_stamp holds the actual timestamp.
`entry_id` holds the timestamp id corresponding to this entry and
`entry_stamp` holds the actual timestamp.
For timestamps stored in the cbmem area, a timestamp_table is allocated
with space for MAX_TIMESTAMPS equal to 30. Thus, the cbmem area holds
base_time, max_entries (which is 30), current number of entries and the
actual entries represented by timestamp_entry.
For timestamps stored in the cbmem area, a `timestamp_table` is allocated
with space for `MAX_TIMESTAMPS` equal to 30. Thus, the cbmem area holds
`base_time`, `max_entries` (which is 30), current number of entries and the
actual entries represented by `timestamp_entry`.
Function APIs
=============
## Function APIs
### timestamp_init
timestamp_init
--------------
This function initializes the timestamp cache and should be run as early
as possible. On platforms with SRAM, this might mean in bootblock, on
x86 with its CAR backed memory in romstage, this means romstage before
memory init.
timestamp_add
-------------
### timestamp_add
This function accepts from user a timestamp id and time to record in the
timestamp table. It stores the entry in the appropriate table in cbmem
or _timestamp region or local stash.
or `_timestamp` region or local stash.
timestamp_add_now
-----------------
This function calls timestamp_add with user-provided id and current time.
### timestamp_add_now
This function calls `timestamp_add` with user-provided id and current time.
Use / Test Cases
================
## Use / Test Cases
The following cases have been considered while designing the timestamp
library. It is important to ensure that any changes made to this library satisfy
each of the following use cases:
Case 1: Timestamp Region Exists (Fresh Boot / Resume)
-----------------------------------------------------
### Case 1: Timestamp Region Exists (Fresh Boot / Resume)
In this case, the library needs to call timestamp_init as early as possible to
In this case, the library needs to call `timestamp_init` as early as possible to
enable the timestamp cache. Once cbmem is available, the values will be
transferred automatically.
All regions are automatically reset on initialization.
Case 2: No timestamp region, fresh boot, cbmem_initialize called after timestamp_init
-------------------------------------------------------------------------------------
### Case 2: No timestamp region, fresh boot, cbmem_initialize called after timestamp_init
timestamp_init will set up a local cache. cbmem must be initialized before that
`timestamp_init` will set up a local cache. cbmem must be initialized before that
cache vanishes - as happens when jumping to the next stage.
Case 3: No timestamp region, fresh boot, cbmem_initialize called before timestamp_init
--------------------------------------------------------------------------------------
### Case 3: No timestamp region, fresh boot, cbmem_initialize called before timestamp_init
This case is not supported right now, just don't call timestamp_init after
cbmem_initialize. (Patches to make this more robust are welcome.)
This case is not supported right now, just don't call `timestamp_init` after
`cbmem_initialize`. (Patches to make this more robust are welcome.)
Case 4: No timestamp region, resume, cbmem_initialize called after timestamp_init
---------------------------------------------------------------------------------
### Case 4: No timestamp region, resume, cbmem_initialize called after timestamp_init
We always reset the cbmem region before using it, so pre-suspend timestamps
will be gone.
Case 5: No timestamp region, resume, cbmem_initialize called before timestamp_init
----------------------------------------------------------------------------------
### Case 5: No timestamp region, resume, cbmem_initialize called before timestamp_init
We always reset the cbmem region before using it, so pre-suspend timestamps
will be gone.