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Fri, 12 Feb 2021 04:15:28 -0800 (PST) From: William Breathitt Gray To: jic23@kernel.org Subject: [PATCH v8 15/22] docs: counter: Update to reflect sysfs internalization Date: Fri, 12 Feb 2021 21:13:39 +0900 Message-Id: <1d1a856e2f081fa6e8619c249c3a0468521c2654.1613131238.git.vilhelm.gray@gmail.com> X-Mailer: git-send-email 2.30.0 In-Reply-To: References: MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210212_071531_222845_F3AACC76 X-CRM114-Status: GOOD ( 23.69 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kamel.bouhara@bootlin.com, gwendal@chromium.org, a.fatoum@pengutronix.de, david@lechnology.com, linux-iio@vger.kernel.org, patrick.havelange@essensium.com, alexandre.belloni@bootlin.com, mcoquelin.stm32@gmail.com, linux-kernel@vger.kernel.org, o.rempel@pengutronix.de, kernel@pengutronix.de, William Breathitt Gray , fabrice.gasnier@st.com, syednwaris@gmail.com, linux-stm32@st-md-mailman.stormreply.com, linux-arm-kernel@lists.infradead.org, alexandre.torgue@st.com Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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. Signed-off-by: William Breathitt Gray --- Documentation/ABI/testing/sysfs-bus-counter | 9 +- Documentation/driver-api/generic-counter.rst | 243 ++++++++++++++----- 2 files changed, 185 insertions(+), 67 deletions(-) diff --git a/Documentation/ABI/testing/sysfs-bus-counter b/Documentation/ABI/testing/sysfs-bus-counter index 29f54484183f..6353f0a2f8f8 100644 --- a/Documentation/ABI/testing/sysfs-bus-counter +++ b/Documentation/ABI/testing/sysfs-bus-counter @@ -277,7 +277,14 @@ What: /sys/bus/counter/devices/counterX/signalY/signal KernelVersion: 5.2 Contact: linux-iio@vger.kernel.org Description: - Signal data of Signal Y represented as a string. + Signal level state of Signal Y. The following signal level + states are available: + + low: + Low level state. + + high: + High level state. What: /sys/bus/counter/devices/counterX/signalY/synchronous_mode KernelVersion: 5.2 diff --git a/Documentation/driver-api/generic-counter.rst b/Documentation/driver-api/generic-counter.rst index 64fe7db080e5..f6397218aa4c 100644 --- a/Documentation/driver-api/generic-counter.rst +++ b/Documentation/driver-api/generic-counter.rst @@ -250,8 +250,8 @@ for defining a counter device. .. kernel-doc:: drivers/counter/counter.c :export: -Implementation -============== +Driver Implementation +===================== To support a counter device, a driver must first allocate the available Counter Signals via counter_signal structures. These Signals should @@ -267,25 +267,61 @@ 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 should be provided to the counter_device structure via -a constant counter_ops 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. +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 defined counter_device structure may be registered to the system by passing it to the counter_register function, and unregistered by passing it to the counter_unregister function. Similarly, the -devm_counter_register and devm_counter_unregister functions may be used -if device memory-managed registration is desired. - -Extension sysfs attributes can be created for auxiliary functionality -and data by passing in defined counter_device_ext, counter_count_ext, -and counter_signal_ext structures. In these cases, the -counter_device_ext structure is used for global/miscellaneous exposure -and configuration of the respective Counter device, while the -counter_count_ext and counter_signal_ext structures allow for auxiliary -exposure and configuration of a specific Count or Signal respectively. +devm_counter_register function may be used if device memory-managed +registration is desired. + +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. @@ -313,52 +349,127 @@ Determining the type of extension to create is a matter of scope. chip overheated via a device extension called "error_overtemp": /sys/bus/counter/devices/counterX/error_overtemp -Architecture -============ - -When the Generic Counter interface counter module is loaded, the -counter_init function is called which registers a bus_type named -"counter" to the system. Subsequently, when the module is unloaded, the -counter_exit function is called which unregisters the bus_type named -"counter" from the system. - -Counter devices are registered to the system via the counter_register -function, and later removed via the counter_unregister function. The -counter_register function establishes a unique ID for the Counter -device and creates a respective sysfs directory, where X is the -mentioned unique ID: - - /sys/bus/counter/devices/counterX - -Sysfs attributes are created within the counterX directory to expose -functionality, configurations, and data relating to the Counts, Signals, -and Synapses of the Counter device, as well as options and information -for the Counter device itself. - -Each Signal has a directory created to house its relevant sysfs -attributes, where Y is the unique ID of the respective Signal: - - /sys/bus/counter/devices/counterX/signalY - -Similarly, each Count has a directory created to house its relevant -sysfs attributes, where Y is the unique ID of the respective Count: - - /sys/bus/counter/devices/counterX/countY - -For a more detailed breakdown of the available Generic Counter interface -sysfs attributes, please refer to the -Documentation/ABI/testing/sysfs-bus-counter file. - -The Signals and Counts associated with the Counter device are registered -to the system as well by the counter_register function. The -signal_read/signal_write driver callbacks are associated with their -respective Signal attributes, while the count_read/count_write and -function_get/function_set driver callbacks are associated with their -respective Count attributes; similarly, the same is true for the -action_get/action_set driver callbacks and their respective Synapse -attributes. If a driver callback is left undefined, then the respective -read/write permission is left disabled for the relevant attributes. - -Similarly, extension sysfs attributes are created for the defined -counter_device_ext, counter_count_ext, and counter_signal_ext -structures that are passed in. +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 + +--------------------+ + | Counter sysfs | + +--------------------+ + | Translates to the | + | standard Counter | + | sysfs output | + +--------------------+ + +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 + +--------------------+ + | Counter sysfs | + +--------------------+ + | Translates to the | + | standard Counter | + | sysfs output | + |--------------------| + | Type: const char * | + | Value: "42" | + +--------------------+ + | + --------------- + / const char * / + --------------- + | + V + +--------------------------------------------------+ + | `/sys/bus/counter/devices/counterX/countY/count` | + +--------------------------------------------------+ + \ Count: "42" / + -------------------------------------------------- + +There are three 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.