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docs: counter: Update to reflect sysfs internalization
The Counter subsystem architecture and driver implementations have changed in order to handle Counter sysfs interactions in a more consistent way. This patch updates the Generic Counter interface documentation to reflect the changes. Reviewed-by: David Lechner <david@lechnology.com> Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com> Link: https://lore.kernel.org/r/91cded13c0145c0d3d0acfe765a2ccb6c9af7c3b.1630031207.git.vilhelm.gray@gmail.com Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
This commit is contained in:
William Breathitt Gray
Jonathan Cameron
parent
712392f558
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de8daf30af
2 changed files with 174 additions and 56 deletions
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@ -286,7 +286,14 @@ What: /sys/bus/counter/devices/counterX/signalY/signal
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KernelVersion: 5.2
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Contact: linux-iio@vger.kernel.org
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Description:
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Signal data of Signal Y represented as a string.
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Signal level state of Signal Y. The following signal level
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states are available:
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low:
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Low level state.
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high:
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High level state.
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What: /sys/bus/counter/devices/counterX/signalY/synchronous_mode
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KernelVersion: 5.2
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@ -250,8 +250,8 @@ for defining a counter device.
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.. kernel-doc:: drivers/counter/counter.c
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:export:
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Implementation
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==============
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Driver Implementation
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=====================
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To support a counter device, a driver must first allocate the available
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Counter Signals via counter_signal structures. These Signals should
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@ -267,25 +267,61 @@ respective counter_count structure. These counter_count structures are
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set to the counts array member of an allocated counter_device structure
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before the Counter is registered to the system.
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Driver callbacks should be provided to the counter_device structure via
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a constant counter_ops structure in order to communicate with the
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device: to read and write various Signals and Counts, and to set and get
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the "action mode" and "function mode" for various Synapses and Counts
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respectively.
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Driver callbacks must be provided to the counter_device structure in
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order to communicate with the device: to read and write various Signals
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and Counts, and to set and get the "action mode" and "function mode" for
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various Synapses and Counts respectively.
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A defined counter_device structure may be registered to the system by
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passing it to the counter_register function, and unregistered by passing
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it to the counter_unregister function. Similarly, the
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devm_counter_register and devm_counter_unregister functions may be used
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if device memory-managed registration is desired.
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devm_counter_register function may be used if device memory-managed
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registration is desired.
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Extension sysfs attributes can be created for auxiliary functionality
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and data by passing in defined counter_device_ext, counter_count_ext,
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and counter_signal_ext structures. In these cases, the
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counter_device_ext structure is used for global/miscellaneous exposure
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and configuration of the respective Counter device, while the
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counter_count_ext and counter_signal_ext structures allow for auxiliary
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exposure and configuration of a specific Count or Signal respectively.
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The struct counter_comp structure is used to define counter extensions
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for Signals, Synapses, and Counts.
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The "type" member specifies the type of high-level data (e.g. BOOL,
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COUNT_DIRECTION, etc.) handled by this extension. The "``*_read``" and
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"``*_write``" members can then be set by the counter device driver with
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callbacks to handle that data using native C data types (i.e. u8, u64,
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etc.).
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Convenience macros such as ``COUNTER_COMP_COUNT_U64`` are provided for
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use by driver authors. In particular, driver authors are expected to use
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the provided macros for standard Counter subsystem attributes in order
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to maintain a consistent interface for userspace. For example, a counter
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device driver may define several standard attributes like so::
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struct counter_comp count_ext[] = {
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COUNTER_COMP_DIRECTION(count_direction_read),
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COUNTER_COMP_ENABLE(count_enable_read, count_enable_write),
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COUNTER_COMP_CEILING(count_ceiling_read, count_ceiling_write),
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};
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This makes it simple to see, add, and modify the attributes that are
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supported by this driver ("direction", "enable", and "ceiling") and to
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maintain this code without getting lost in a web of struct braces.
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Callbacks must match the function type expected for the respective
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component or extension. These function types are defined in the struct
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counter_comp structure as the "``*_read``" and "``*_write``" union
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members.
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The corresponding callback prototypes for the extensions mentioned in
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the previous example above would be::
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int count_direction_read(struct counter_device *counter,
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struct counter_count *count,
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enum counter_count_direction *direction);
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int count_enable_read(struct counter_device *counter,
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struct counter_count *count, u8 *enable);
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int count_enable_write(struct counter_device *counter,
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struct counter_count *count, u8 enable);
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int count_ceiling_read(struct counter_device *counter,
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struct counter_count *count, u64 *ceiling);
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int count_ceiling_write(struct counter_device *counter,
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struct counter_count *count, u64 ceiling);
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Determining the type of extension to create is a matter of scope.
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@ -313,52 +349,127 @@ Determining the type of extension to create is a matter of scope.
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chip overheated via a device extension called "error_overtemp":
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/sys/bus/counter/devices/counterX/error_overtemp
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Architecture
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============
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Subsystem Architecture
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======================
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When the Generic Counter interface counter module is loaded, the
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counter_init function is called which registers a bus_type named
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"counter" to the system. Subsequently, when the module is unloaded, the
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counter_exit function is called which unregisters the bus_type named
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"counter" from the system.
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Counter drivers pass and take data natively (i.e. ``u8``, ``u64``, etc.)
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and the shared counter module handles the translation between the sysfs
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interface. This guarantees a standard userspace interface for all
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counter drivers, and enables a Generic Counter chrdev interface via a
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generalized device driver ABI.
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Counter devices are registered to the system via the counter_register
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function, and later removed via the counter_unregister function. The
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counter_register function establishes a unique ID for the Counter
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device and creates a respective sysfs directory, where X is the
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mentioned unique ID:
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A high-level view of how a count value is passed down from a counter
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driver is exemplified by the following. The driver callbacks are first
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registered to the Counter core component for use by the Counter
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userspace interface components::
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/sys/bus/counter/devices/counterX
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Driver callbacks registration:
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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+----------------------------+
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| Counter device driver |
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+----------------------------+
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| Processes data from device |
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+----------------------------+
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-------------------
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/ driver callbacks /
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-------------------
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V
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+----------------------+
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| Counter core |
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+----------------------+
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| Routes device driver |
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| callbacks to the |
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| userspace interfaces |
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+----------------------+
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-------------------
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/ driver callbacks /
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-------------------
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+---------------+
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V
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+--------------------+
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| Counter sysfs |
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+--------------------+
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| Translates to the |
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| standard Counter |
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| sysfs output |
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+--------------------+
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Sysfs attributes are created within the counterX directory to expose
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functionality, configurations, and data relating to the Counts, Signals,
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and Synapses of the Counter device, as well as options and information
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for the Counter device itself.
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Thereafter, data can be transferred directly between the Counter device
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driver and Counter userspace interface::
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Each Signal has a directory created to house its relevant sysfs
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attributes, where Y is the unique ID of the respective Signal:
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Count data request:
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~~~~~~~~~~~~~~~~~~~
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----------------------
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/ Counter device \
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+----------------------+
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| Count register: 0x28 |
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+----------------------+
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-----------------
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/ raw count data /
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-----------------
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V
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+----------------------------+
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| Counter device driver |
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+----------------------------+
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| Processes data from device |
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|----------------------------|
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| Type: u64 |
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| Value: 42 |
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+----------------------------+
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----------
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/ u64 /
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----------
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+---------------+
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V
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+--------------------+
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| Counter sysfs |
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+--------------------+
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| Translates to the |
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| standard Counter |
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| sysfs output |
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|--------------------|
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| Type: const char * |
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| Value: "42" |
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+--------------------+
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---------------
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/ const char * /
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---------------
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V
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+--------------------------------------------------+
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| `/sys/bus/counter/devices/counterX/countY/count` |
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+--------------------------------------------------+
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\ Count: "42" /
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--------------------------------------------------
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/sys/bus/counter/devices/counterX/signalY
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There are three primary components involved:
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Similarly, each Count has a directory created to house its relevant
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sysfs attributes, where Y is the unique ID of the respective Count:
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Counter device driver
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---------------------
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Communicates with the hardware device to read/write data; e.g. counter
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drivers for quadrature encoders, timers, etc.
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/sys/bus/counter/devices/counterX/countY
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Counter core
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------------
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Registers the counter device driver to the system so that the respective
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callbacks are called during userspace interaction.
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For a more detailed breakdown of the available Generic Counter interface
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sysfs attributes, please refer to the
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Documentation/ABI/testing/sysfs-bus-counter file.
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Counter sysfs
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-------------
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Translates counter data to the standard Counter sysfs interface format
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and vice versa.
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The Signals and Counts associated with the Counter device are registered
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to the system as well by the counter_register function. The
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signal_read/signal_write driver callbacks are associated with their
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respective Signal attributes, while the count_read/count_write and
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function_get/function_set driver callbacks are associated with their
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respective Count attributes; similarly, the same is true for the
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action_get/action_set driver callbacks and their respective Synapse
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attributes. If a driver callback is left undefined, then the respective
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read/write permission is left disabled for the relevant attributes.
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Similarly, extension sysfs attributes are created for the defined
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counter_device_ext, counter_count_ext, and counter_signal_ext
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structures that are passed in.
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Please refer to the ``Documentation/ABI/testing/sysfs-bus-counter`` file
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for a detailed breakdown of the available Generic Counter interface
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sysfs attributes.
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