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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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Documentation/timestamp.md
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@ -1,33 +1,31 @@
Table of Contents # Timestamps
=================
## Table of Contents
Introduction Introduction
Transition from cache to cbmem - Transition from cache to cbmem
Data structures used Data structures used
cache_state - cache_state
table - table
entries - entries
Function APIs Function APIs
timestamp_init - timestamp_init
timestamp_add - timestamp_add
timestamp_add_now - timestamp_add_now
timestamp_sync - timestamp_sync
Use / Test Cases Use / Test Cases
Case 1: Timestamp Region Exists - Case 1: Timestamp Region Exists
Case 2: No timestamp region, fresh boot, cbmem_initialize called after - Case 2: No timestamp region, fresh boot, cbmem_initialize called after timestamp_init
timestamp_init - Case 3: No timestamp region, fresh boot, cbmem_initialize called before timestamp_init
Case 3: No timestamp region, fresh boot, cbmem_initialize called before - Case 4: No timestamp region, resume, cbmem_initialize called after timestamp_init
timestamp_init - Case 5: No timestamp region, resume, 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 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 to save timestamps in cbmem / stash (until cbmem is brought up) by
providing a simple API to initialize, add and sync timestamps. In order 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 3. Add a new cbmem timestamp area based on whether a reset of the cbmem
timestamp region is required or not. 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 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. 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. 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: The main structure that maintains information about the timestamp cache is:
```
struct __packed timestamp_cache { struct __packed timestamp_cache {
uint16_t cache_state; uint16_t cache_state;
struct timestamp_table table; struct timestamp_table table;
struct timestamp_entry entries[MAX_TIMESTAMP_CACHE]; struct timestamp_entry entries[MAX_TIMESTAMP_CACHE];
}; };
```
cache_state ### cache_state
-----------
The state of the cache is maintained by cache_state attribute which can The state of the cache is maintained by `cache_state` attribute which can
be any one of the following: be any one of the following:
```
enum { enum {
TIMESTAMP_CACHE_UNINITIALIZED = 0, TIMESTAMP_CACHE_UNINITIALIZED = 0,
TIMESTAMP_CACHE_INITIALIZED, TIMESTAMP_CACHE_INITIALIZED,
TIMESTAMP_CACHE_NOT_NEEDED, TIMESTAMP_CACHE_NOT_NEEDED,
}; };
```
By default, if the cache is stored in local stash (bss area), then 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 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. initialized to default values by the library.
Once the cache is initialized, its state is set to 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 know that the state reflected is valid and timestamps can be directly
saved in the cache. 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 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 anymore. Thus, the cache state is set to `CACHE_NOT_NEEDED`, which allows
timestamp_add to store all timestamps directly into the cbmem area. `timestamp_add` to store all timestamps directly into the cbmem area.
table ### table
-----
This field is represented by a structure which provides overall This field is represented by a structure which provides overall
information about the entries in the timestamp area: information about the entries in the timestamp area:
```
struct timestamp_table { struct timestamp_table {
uint64_t base_time; uint64_t base_time;
uint32_t max_entries; uint32_t max_entries;
uint32_t num_entries; uint32_t num_entries;
struct timestamp_entry entries[0]; /* Variable number of entries */ struct timestamp_entry entries[0]; /* Variable number of entries */
} __packed; } __packed;
```
It indicates the base time for all timestamp entries, maximum number It indicates the base time for all timestamp entries, maximum number
of entries that can be stored, total number of entries that currently of entries that can be stored, total number of entries that currently
exist and an entry structure to hold variable number of entries. 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 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: defined by:
```
struct timestamp_entry { struct timestamp_entry {
uint32_t entry_id; uint32_t entry_id;
uint64_t entry_stamp; uint64_t entry_stamp;
} __packed; } __packed;
```
entry_id holds the timestamp id corresponding to this entry and `entry_id` holds the timestamp id corresponding to this entry and
entry_stamp holds the actual timestamp. `entry_stamp` holds the actual timestamp.
For timestamps stored in the cbmem area, a timestamp_table is allocated 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 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 `base_time`, `max_entries` (which is 30), current number of entries and the
actual entries represented by timestamp_entry. 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 This function initializes the timestamp cache and should be run as early
as possible. On platforms with SRAM, this might mean in bootblock, on as possible. On platforms with SRAM, this might mean in bootblock, on
x86 with its CAR backed memory in romstage, this means romstage before x86 with its CAR backed memory in romstage, this means romstage before
memory init. memory init.
timestamp_add ### timestamp_add
-------------
This function accepts from user a timestamp id and time to record in the 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 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 ### timestamp_add_now
-----------------
This function calls timestamp_add with user-provided id and current time. 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 The following cases have been considered while designing the timestamp
library. It is important to ensure that any changes made to this library satisfy library. It is important to ensure that any changes made to this library satisfy
each of the following use cases: 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 enable the timestamp cache. Once cbmem is available, the values will be
transferred automatically. transferred automatically.
All regions are automatically reset on initialization. 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. 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 This case is not supported right now, just don't call `timestamp_init` after
cbmem_initialize. (Patches to make this more robust are welcome.) `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 We always reset the cbmem region before using it, so pre-suspend timestamps
will be gone. 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 We always reset the cbmem region before using it, so pre-suspend timestamps
will be gone. will be gone.