201 lines
7.0 KiB
Markdown
201 lines
7.0 KiB
Markdown
Table of Contents
|
|
=================
|
|
Introduction
|
|
Transition from cache to cbmem
|
|
|
|
Data structures used
|
|
cache_state
|
|
table
|
|
entries
|
|
|
|
Function APIs
|
|
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
|
|
|
|
|
|
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
|
|
to make the timestamps persistent and accessible from the kernel, we
|
|
need to ensure that all the saved timestamps end up in cbmem under
|
|
the CBMEM_ID_TIMESTAMP tag. However, until the cbmem area is available,
|
|
the timestamps can be saved to a SoC-defined \_timestamp region or in a
|
|
local stage-specific stash. The work of identifying the right location for
|
|
storing timestamps is done by the library and is not exposed to the user.
|
|
|
|
Working of timestamp library from a user perspective can be outlined in
|
|
the following steps:
|
|
1. Initialize the base time and reset cbmem timestamp area
|
|
2. Start adding timestamps
|
|
|
|
Behind the scenes, the timestamp library takes care of:
|
|
1. Identifying the correct location for storing timestamps (cbmem or timestamp
|
|
region or local stash).
|
|
2. Once cbmem is up, ensure that all timestamps are synced from timestamp
|
|
region or local stash into the cbmem area.
|
|
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
|
|
------------------------------
|
|
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.
|
|
|
|
When cbmem is initialized, the hook is called, which creates the area,
|
|
copies all timestamps to cbmem and disables the cache.
|
|
|
|
After such a transition, timestamp_init() must not be run again.
|
|
|
|
|
|
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
|
|
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
|
|
stored in timestamp region, then it might have garbage in any of the
|
|
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
|
|
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),
|
|
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.
|
|
|
|
|
|
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
|
|
-------
|
|
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
|
|
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.
|
|
|
|
|
|
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
|
|
=============
|
|
|
|
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
|
|
-------------
|
|
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.
|
|
|
|
|
|
timestamp_add_now
|
|
-----------------
|
|
This function calls timestamp_add with user-provided id and current time.
|
|
|
|
|
|
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)
|
|
-----------------------------------------------------
|
|
|
|
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
|
|
-------------------------------------------------------------------------------------
|
|
|
|
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
|
|
--------------------------------------------------------------------------------------
|
|
|
|
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
|
|
---------------------------------------------------------------------------------
|
|
|
|
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
|
|
----------------------------------------------------------------------------------
|
|
|
|
We always reset the cbmem region before using it, so pre-suspend timestamps
|
|
will be gone.
|