574 строки
24 KiB
ReStructuredText
574 строки
24 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
|
|
|
|
=========================
|
|
Generic Counter Interface
|
|
=========================
|
|
|
|
Introduction
|
|
============
|
|
|
|
Counter devices are prevalent among a diverse spectrum of industries.
|
|
The ubiquitous presence of these devices necessitates a common interface
|
|
and standard of interaction and exposure. This driver API attempts to
|
|
resolve the issue of duplicate code found among existing counter device
|
|
drivers by introducing a generic counter interface for consumption. The
|
|
Generic Counter interface enables drivers to support and expose a common
|
|
set of components and functionality present in counter devices.
|
|
|
|
Theory
|
|
======
|
|
|
|
Counter devices can vary greatly in design, but regardless of whether
|
|
some devices are quadrature encoder counters or tally counters, all
|
|
counter devices consist of a core set of components. This core set of
|
|
components, shared by all counter devices, is what forms the essence of
|
|
the Generic Counter interface.
|
|
|
|
There are three core components to a counter:
|
|
|
|
* Signal:
|
|
Stream of data to be evaluated by the counter.
|
|
|
|
* Synapse:
|
|
Association of a Signal, and evaluation trigger, with a Count.
|
|
|
|
* Count:
|
|
Accumulation of the effects of connected Synapses.
|
|
|
|
SIGNAL
|
|
------
|
|
A Signal represents a stream of data. This is the input data that is
|
|
evaluated by the counter to determine the count data; e.g. a quadrature
|
|
signal output line of a rotary encoder. Not all counter devices provide
|
|
user access to the Signal data, so exposure is optional for drivers.
|
|
|
|
When the Signal data is available for user access, the Generic Counter
|
|
interface provides the following available signal values:
|
|
|
|
* SIGNAL_LOW:
|
|
Signal line is in a low state.
|
|
|
|
* SIGNAL_HIGH:
|
|
Signal line is in a high state.
|
|
|
|
A Signal may be associated with one or more Counts.
|
|
|
|
SYNAPSE
|
|
-------
|
|
A Synapse represents the association of a Signal with a Count. Signal
|
|
data affects respective Count data, and the Synapse represents this
|
|
relationship.
|
|
|
|
The Synapse action mode specifies the Signal data condition that
|
|
triggers the respective Count's count function evaluation to update the
|
|
count data. The Generic Counter interface provides the following
|
|
available action modes:
|
|
|
|
* None:
|
|
Signal does not trigger the count function. In Pulse-Direction count
|
|
function mode, this Signal is evaluated as Direction.
|
|
|
|
* Rising Edge:
|
|
Low state transitions to high state.
|
|
|
|
* Falling Edge:
|
|
High state transitions to low state.
|
|
|
|
* Both Edges:
|
|
Any state transition.
|
|
|
|
A counter is defined as a set of input signals associated with count
|
|
data that are generated by the evaluation of the state of the associated
|
|
input signals as defined by the respective count functions. Within the
|
|
context of the Generic Counter interface, a counter consists of Counts
|
|
each associated with a set of Signals, whose respective Synapse
|
|
instances represent the count function update conditions for the
|
|
associated Counts.
|
|
|
|
A Synapse associates one Signal with one Count.
|
|
|
|
COUNT
|
|
-----
|
|
A Count represents the accumulation of the effects of connected
|
|
Synapses; i.e. the count data for a set of Signals. The Generic
|
|
Counter interface represents the count data as a natural number.
|
|
|
|
A Count has a count function mode which represents the update behavior
|
|
for the count data. The Generic Counter interface provides the following
|
|
available count function modes:
|
|
|
|
* Increase:
|
|
Accumulated count is incremented.
|
|
|
|
* Decrease:
|
|
Accumulated count is decremented.
|
|
|
|
* Pulse-Direction:
|
|
Rising edges on signal A updates the respective count. The input level
|
|
of signal B determines direction.
|
|
|
|
* Quadrature:
|
|
A pair of quadrature encoding signals are evaluated to determine
|
|
position and direction. The following Quadrature modes are available:
|
|
|
|
- x1 A:
|
|
If direction is forward, rising edges on quadrature pair signal A
|
|
updates the respective count; if the direction is backward, falling
|
|
edges on quadrature pair signal A updates the respective count.
|
|
Quadrature encoding determines the direction.
|
|
|
|
- x1 B:
|
|
If direction is forward, rising edges on quadrature pair signal B
|
|
updates the respective count; if the direction is backward, falling
|
|
edges on quadrature pair signal B updates the respective count.
|
|
Quadrature encoding determines the direction.
|
|
|
|
- x2 A:
|
|
Any state transition on quadrature pair signal A updates the
|
|
respective count. Quadrature encoding determines the direction.
|
|
|
|
- x2 B:
|
|
Any state transition on quadrature pair signal B updates the
|
|
respective count. Quadrature encoding determines the direction.
|
|
|
|
- x4:
|
|
Any state transition on either quadrature pair signals updates the
|
|
respective count. Quadrature encoding determines the direction.
|
|
|
|
A Count has a set of one or more associated Synapses.
|
|
|
|
Paradigm
|
|
========
|
|
|
|
The most basic counter device may be expressed as a single Count
|
|
associated with a single Signal via a single Synapse. Take for example
|
|
a counter device which simply accumulates a count of rising edges on a
|
|
source input line::
|
|
|
|
Count Synapse Signal
|
|
----- ------- ------
|
|
+---------------------+
|
|
| Data: Count | Rising Edge ________
|
|
| Function: Increase | <------------- / Source \
|
|
| | ____________
|
|
+---------------------+
|
|
|
|
In this example, the Signal is a source input line with a pulsing
|
|
voltage, while the Count is a persistent count value which is repeatedly
|
|
incremented. The Signal is associated with the respective Count via a
|
|
Synapse. The increase function is triggered by the Signal data condition
|
|
specified by the Synapse -- in this case a rising edge condition on the
|
|
voltage input line. In summary, the counter device existence and
|
|
behavior is aptly represented by respective Count, Signal, and Synapse
|
|
components: a rising edge condition triggers an increase function on an
|
|
accumulating count datum.
|
|
|
|
A counter device is not limited to a single Signal; in fact, in theory
|
|
many Signals may be associated with even a single Count. For example, a
|
|
quadrature encoder counter device can keep track of position based on
|
|
the states of two input lines::
|
|
|
|
Count Synapse Signal
|
|
----- ------- ------
|
|
+-------------------------+
|
|
| Data: Position | Both Edges ___
|
|
| Function: Quadrature x4 | <------------ / A \
|
|
| | _______
|
|
| |
|
|
| | Both Edges ___
|
|
| | <------------ / B \
|
|
| | _______
|
|
+-------------------------+
|
|
|
|
In this example, two Signals (quadrature encoder lines A and B) are
|
|
associated with a single Count: a rising or falling edge on either A or
|
|
B triggers the "Quadrature x4" function which determines the direction
|
|
of movement and updates the respective position data. The "Quadrature
|
|
x4" function is likely implemented in the hardware of the quadrature
|
|
encoder counter device; the Count, Signals, and Synapses simply
|
|
represent this hardware behavior and functionality.
|
|
|
|
Signals associated with the same Count can have differing Synapse action
|
|
mode conditions. For example, a quadrature encoder counter device
|
|
operating in a non-quadrature Pulse-Direction mode could have one input
|
|
line dedicated for movement and a second input line dedicated for
|
|
direction::
|
|
|
|
Count Synapse Signal
|
|
----- ------- ------
|
|
+---------------------------+
|
|
| Data: Position | Rising Edge ___
|
|
| Function: Pulse-Direction | <------------- / A \ (Movement)
|
|
| | _______
|
|
| |
|
|
| | None ___
|
|
| | <------------- / B \ (Direction)
|
|
| | _______
|
|
+---------------------------+
|
|
|
|
Only Signal A triggers the "Pulse-Direction" update function, but the
|
|
instantaneous state of Signal B is still required in order to know the
|
|
direction so that the position data may be properly updated. Ultimately,
|
|
both Signals are associated with the same Count via two respective
|
|
Synapses, but only one Synapse has an active action mode condition which
|
|
triggers the respective count function while the other is left with a
|
|
"None" condition action mode to indicate its respective Signal's
|
|
availability for state evaluation despite its non-triggering mode.
|
|
|
|
Keep in mind that the Signal, Synapse, and Count are abstract
|
|
representations which do not need to be closely married to their
|
|
respective physical sources. This allows the user of a counter to
|
|
divorce themselves from the nuances of physical components (such as
|
|
whether an input line is differential or single-ended) and instead focus
|
|
on the core idea of what the data and process represent (e.g. position
|
|
as interpreted from quadrature encoding data).
|
|
|
|
Driver API
|
|
==========
|
|
|
|
Driver authors may utilize the Generic Counter interface in their code
|
|
by including the include/linux/counter.h header file. This header file
|
|
provides several core data structures, function prototypes, and macros
|
|
for defining a counter device.
|
|
|
|
.. kernel-doc:: include/linux/counter.h
|
|
:internal:
|
|
|
|
.. kernel-doc:: drivers/counter/counter-core.c
|
|
:export:
|
|
|
|
.. kernel-doc:: drivers/counter/counter-chrdev.c
|
|
:export:
|
|
|
|
Driver Implementation
|
|
=====================
|
|
|
|
To support a counter device, a driver must first allocate the available
|
|
Counter Signals via counter_signal structures. These Signals should
|
|
be stored as an array and set to the signals array member of an
|
|
allocated counter_device structure before the Counter is registered to
|
|
the system.
|
|
|
|
Counter Counts may be allocated via counter_count structures, and
|
|
respective Counter Signal associations (Synapses) made via
|
|
counter_synapse structures. Associated counter_synapse structures are
|
|
stored as an array and set to the synapses array member of the
|
|
respective counter_count structure. These counter_count structures are
|
|
set to the counts array member of an allocated counter_device structure
|
|
before the Counter is registered to the system.
|
|
|
|
Driver callbacks must be provided to the counter_device structure in
|
|
order to communicate with the device: to read and write various Signals
|
|
and Counts, and to set and get the "action mode" and "function mode" for
|
|
various Synapses and Counts respectively.
|
|
|
|
A counter_device structure is allocated using counter_alloc() and then
|
|
registered to the system by passing it to the counter_add() function, and
|
|
unregistered by passing it to the counter_unregister function. There are
|
|
device managed variants of these functions: devm_counter_alloc() and
|
|
devm_counter_add().
|
|
|
|
The struct counter_comp structure is used to define counter extensions
|
|
for Signals, Synapses, and Counts.
|
|
|
|
The "type" member specifies the type of high-level data (e.g. BOOL,
|
|
COUNT_DIRECTION, etc.) handled by this extension. The "``*_read``" and
|
|
"``*_write``" members can then be set by the counter device driver with
|
|
callbacks to handle that data using native C data types (i.e. u8, u64,
|
|
etc.).
|
|
|
|
Convenience macros such as ``COUNTER_COMP_COUNT_U64`` are provided for
|
|
use by driver authors. In particular, driver authors are expected to use
|
|
the provided macros for standard Counter subsystem attributes in order
|
|
to maintain a consistent interface for userspace. For example, a counter
|
|
device driver may define several standard attributes like so::
|
|
|
|
struct counter_comp count_ext[] = {
|
|
COUNTER_COMP_DIRECTION(count_direction_read),
|
|
COUNTER_COMP_ENABLE(count_enable_read, count_enable_write),
|
|
COUNTER_COMP_CEILING(count_ceiling_read, count_ceiling_write),
|
|
};
|
|
|
|
This makes it simple to see, add, and modify the attributes that are
|
|
supported by this driver ("direction", "enable", and "ceiling") and to
|
|
maintain this code without getting lost in a web of struct braces.
|
|
|
|
Callbacks must match the function type expected for the respective
|
|
component or extension. These function types are defined in the struct
|
|
counter_comp structure as the "``*_read``" and "``*_write``" union
|
|
members.
|
|
|
|
The corresponding callback prototypes for the extensions mentioned in
|
|
the previous example above would be::
|
|
|
|
int count_direction_read(struct counter_device *counter,
|
|
struct counter_count *count,
|
|
enum counter_count_direction *direction);
|
|
int count_enable_read(struct counter_device *counter,
|
|
struct counter_count *count, u8 *enable);
|
|
int count_enable_write(struct counter_device *counter,
|
|
struct counter_count *count, u8 enable);
|
|
int count_ceiling_read(struct counter_device *counter,
|
|
struct counter_count *count, u64 *ceiling);
|
|
int count_ceiling_write(struct counter_device *counter,
|
|
struct counter_count *count, u64 ceiling);
|
|
|
|
Determining the type of extension to create is a matter of scope.
|
|
|
|
* Signal extensions are attributes that expose information/control
|
|
specific to a Signal. These types of attributes will exist under a
|
|
Signal's directory in sysfs.
|
|
|
|
For example, if you have an invert feature for a Signal, you can have
|
|
a Signal extension called "invert" that toggles that feature:
|
|
/sys/bus/counter/devices/counterX/signalY/invert
|
|
|
|
* Count extensions are attributes that expose information/control
|
|
specific to a Count. These type of attributes will exist under a
|
|
Count's directory in sysfs.
|
|
|
|
For example, if you want to pause/unpause a Count from updating, you
|
|
can have a Count extension called "enable" that toggles such:
|
|
/sys/bus/counter/devices/counterX/countY/enable
|
|
|
|
* Device extensions are attributes that expose information/control
|
|
non-specific to a particular Count or Signal. This is where you would
|
|
put your global features or other miscellaneous functionality.
|
|
|
|
For example, if your device has an overtemp sensor, you can report the
|
|
chip overheated via a device extension called "error_overtemp":
|
|
/sys/bus/counter/devices/counterX/error_overtemp
|
|
|
|
Subsystem Architecture
|
|
======================
|
|
|
|
Counter drivers pass and take data natively (i.e. ``u8``, ``u64``, etc.)
|
|
and the shared counter module handles the translation between the sysfs
|
|
interface. This guarantees a standard userspace interface for all
|
|
counter drivers, and enables a Generic Counter chrdev interface via a
|
|
generalized device driver ABI.
|
|
|
|
A high-level view of how a count value is passed down from a counter
|
|
driver is exemplified by the following. The driver callbacks are first
|
|
registered to the Counter core component for use by the Counter
|
|
userspace interface components::
|
|
|
|
Driver callbacks registration:
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
+----------------------------+
|
|
| Counter device driver |
|
|
+----------------------------+
|
|
| Processes data from device |
|
|
+----------------------------+
|
|
|
|
|
-------------------
|
|
/ driver callbacks /
|
|
-------------------
|
|
|
|
|
V
|
|
+----------------------+
|
|
| Counter core |
|
|
+----------------------+
|
|
| Routes device driver |
|
|
| callbacks to the |
|
|
| userspace interfaces |
|
|
+----------------------+
|
|
|
|
|
-------------------
|
|
/ driver callbacks /
|
|
-------------------
|
|
|
|
|
+---------------+---------------+
|
|
| |
|
|
V V
|
|
+--------------------+ +---------------------+
|
|
| Counter sysfs | | Counter chrdev |
|
|
+--------------------+ +---------------------+
|
|
| Translates to the | | Translates to the |
|
|
| standard Counter | | standard Counter |
|
|
| sysfs output | | character device |
|
|
+--------------------+ +---------------------+
|
|
|
|
Thereafter, data can be transferred directly between the Counter device
|
|
driver and Counter userspace interface::
|
|
|
|
Count data request:
|
|
~~~~~~~~~~~~~~~~~~~
|
|
----------------------
|
|
/ Counter device \
|
|
+----------------------+
|
|
| Count register: 0x28 |
|
|
+----------------------+
|
|
|
|
|
-----------------
|
|
/ raw count data /
|
|
-----------------
|
|
|
|
|
V
|
|
+----------------------------+
|
|
| Counter device driver |
|
|
+----------------------------+
|
|
| Processes data from device |
|
|
|----------------------------|
|
|
| Type: u64 |
|
|
| Value: 42 |
|
|
+----------------------------+
|
|
|
|
|
----------
|
|
/ u64 /
|
|
----------
|
|
|
|
|
+---------------+---------------+
|
|
| |
|
|
V V
|
|
+--------------------+ +---------------------+
|
|
| Counter sysfs | | Counter chrdev |
|
|
+--------------------+ +---------------------+
|
|
| Translates to the | | Translates to the |
|
|
| standard Counter | | standard Counter |
|
|
| sysfs output | | character device |
|
|
|--------------------| |---------------------|
|
|
| Type: const char * | | Type: u64 |
|
|
| Value: "42" | | Value: 42 |
|
|
+--------------------+ +---------------------+
|
|
| |
|
|
--------------- -----------------------
|
|
/ const char * / / struct counter_event /
|
|
--------------- -----------------------
|
|
| |
|
|
| V
|
|
| +-----------+
|
|
| | read |
|
|
| +-----------+
|
|
| \ Count: 42 /
|
|
| -----------
|
|
|
|
|
V
|
|
+--------------------------------------------------+
|
|
| `/sys/bus/counter/devices/counterX/countY/count` |
|
|
+--------------------------------------------------+
|
|
\ Count: "42" /
|
|
--------------------------------------------------
|
|
|
|
There are four primary components involved:
|
|
|
|
Counter device driver
|
|
---------------------
|
|
Communicates with the hardware device to read/write data; e.g. counter
|
|
drivers for quadrature encoders, timers, etc.
|
|
|
|
Counter core
|
|
------------
|
|
Registers the counter device driver to the system so that the respective
|
|
callbacks are called during userspace interaction.
|
|
|
|
Counter sysfs
|
|
-------------
|
|
Translates counter data to the standard Counter sysfs interface format
|
|
and vice versa.
|
|
|
|
Please refer to the ``Documentation/ABI/testing/sysfs-bus-counter`` file
|
|
for a detailed breakdown of the available Generic Counter interface
|
|
sysfs attributes.
|
|
|
|
Counter chrdev
|
|
--------------
|
|
Translates Counter events to the standard Counter character device; data
|
|
is transferred via standard character device read calls, while Counter
|
|
events are configured via ioctl calls.
|
|
|
|
Sysfs Interface
|
|
===============
|
|
|
|
Several sysfs attributes are generated by the Generic Counter interface,
|
|
and reside under the ``/sys/bus/counter/devices/counterX`` directory,
|
|
where ``X`` is to the respective counter device id. Please see
|
|
``Documentation/ABI/testing/sysfs-bus-counter`` for detailed information
|
|
on each Generic Counter interface sysfs attribute.
|
|
|
|
Through these sysfs attributes, programs and scripts may interact with
|
|
the Generic Counter paradigm Counts, Signals, and Synapses of respective
|
|
counter devices.
|
|
|
|
Counter Character Device
|
|
========================
|
|
|
|
Counter character device nodes are created under the ``/dev`` directory
|
|
as ``counterX``, where ``X`` is the respective counter device id.
|
|
Defines for the standard Counter data types are exposed via the
|
|
userspace ``include/uapi/linux/counter.h`` file.
|
|
|
|
Counter events
|
|
--------------
|
|
Counter device drivers can support Counter events by utilizing the
|
|
``counter_push_event`` function::
|
|
|
|
void counter_push_event(struct counter_device *const counter, const u8 event,
|
|
const u8 channel);
|
|
|
|
The event id is specified by the ``event`` parameter; the event channel
|
|
id is specified by the ``channel`` parameter. When this function is
|
|
called, the Counter data associated with the respective event is
|
|
gathered, and a ``struct counter_event`` is generated for each datum and
|
|
pushed to userspace.
|
|
|
|
Counter events can be configured by users to report various Counter
|
|
data of interest. This can be conceptualized as a list of Counter
|
|
component read calls to perform. For example:
|
|
|
|
+------------------------+------------------------+
|
|
| COUNTER_EVENT_OVERFLOW | COUNTER_EVENT_INDEX |
|
|
+========================+========================+
|
|
| Channel 0 | Channel 0 |
|
|
+------------------------+------------------------+
|
|
| * Count 0 | * Signal 0 |
|
|
| * Count 1 | * Signal 0 Extension 0 |
|
|
| * Signal 3 | * Extension 4 |
|
|
| * Count 4 Extension 2 +------------------------+
|
|
| * Signal 5 Extension 0 | Channel 1 |
|
|
| +------------------------+
|
|
| | * Signal 4 |
|
|
| | * Signal 4 Extension 0 |
|
|
| | * Count 7 |
|
|
+------------------------+------------------------+
|
|
|
|
When ``counter_push_event(counter, COUNTER_EVENT_INDEX, 1)`` is called
|
|
for example, it will go down the list for the ``COUNTER_EVENT_INDEX``
|
|
event channel 1 and execute the read callbacks for Signal 4, Signal 4
|
|
Extension 0, and Count 7 -- the data returned for each is pushed to a
|
|
kfifo as a ``struct counter_event``, which userspace can retrieve via a
|
|
standard read operation on the respective character device node.
|
|
|
|
Userspace
|
|
---------
|
|
Userspace applications can configure Counter events via ioctl operations
|
|
on the Counter character device node. There following ioctl codes are
|
|
supported and provided by the ``linux/counter.h`` userspace header file:
|
|
|
|
* :c:macro:`COUNTER_ADD_WATCH_IOCTL`
|
|
|
|
* :c:macro:`COUNTER_ENABLE_EVENTS_IOCTL`
|
|
|
|
* :c:macro:`COUNTER_DISABLE_EVENTS_IOCTL`
|
|
|
|
To configure events to gather Counter data, users first populate a
|
|
``struct counter_watch`` with the relevant event id, event channel id,
|
|
and the information for the desired Counter component from which to
|
|
read, and then pass it via the ``COUNTER_ADD_WATCH_IOCTL`` ioctl
|
|
command.
|
|
|
|
Note that an event can be watched without gathering Counter data by
|
|
setting the ``component.type`` member equal to
|
|
``COUNTER_COMPONENT_NONE``. With this configuration the Counter
|
|
character device will simply populate the event timestamps for those
|
|
respective ``struct counter_event`` elements and ignore the component
|
|
value.
|
|
|
|
The ``COUNTER_ADD_WATCH_IOCTL`` command will buffer these Counter
|
|
watches. When ready, the ``COUNTER_ENABLE_EVENTS_IOCTL`` ioctl command
|
|
may be used to activate these Counter watches.
|
|
|
|
Userspace applications can then execute a ``read`` operation (optionally
|
|
calling ``poll`` first) on the Counter character device node to retrieve
|
|
``struct counter_event`` elements with the desired data.
|