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[72.189.64.225]) by smtp.gmail.com with ESMTPSA id j72sm3331351qke.20.2020.07.21.12.36.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Jul 2020 12:36:14 -0700 (PDT) From: William Breathitt Gray To: jic23@kernel.org Cc: kamel.bouhara@bootlin.com, gwendal@chromium.org, alexandre.belloni@bootlin.com, david@lechnology.com, linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com, linux-arm-kernel@lists.infradead.org, syednwaris@gmail.com, patrick.havelange@essensium.com, fabrice.gasnier@st.com, mcoquelin.stm32@gmail.com, alexandre.torgue@st.com, William Breathitt Gray Subject: [PATCH v4 4/5] docs: counter: Document character device interface Date: Tue, 21 Jul 2020 15:35:50 -0400 Message-Id: X-Mailer: git-send-email 2.27.0 In-Reply-To: References: MIME-Version: 1.0 Sender: linux-iio-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-iio@vger.kernel.org This patch adds high-level documentation about the Counter subsystem character device interface. Signed-off-by: William Breathitt Gray --- Documentation/driver-api/generic-counter.rst | 191 +++++++++++++++--- .../userspace-api/ioctl/ioctl-number.rst | 1 + 2 files changed, 160 insertions(+), 32 deletions(-) diff --git a/Documentation/driver-api/generic-counter.rst b/Documentation/driver-api/generic-counter.rst index fa2d699d44a5..a5f2e8dc430c 100644 --- a/Documentation/driver-api/generic-counter.rst +++ b/Documentation/driver-api/generic-counter.rst @@ -223,19 +223,6 @@ 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). -Userspace Interface -=================== - -Several sysfs attributes are generated by the Generic Counter interface, -and reside under the /sys/bus/counter/devices/counterX directory, where -counterX refers to the respective counter device. 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. - Driver API ========== @@ -399,25 +386,32 @@ driver is exemplified by the following:: | / driver callbacks / | ------------------- | | - +-------+ | + +-------+---------------+ | + | | | + | +-------|-------+ + | | | + 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 | + +--------------------+ +---------------------+ | | - | +---------------+ - | | - V | - +--------------------+ | - | Counter sysfs |<-+ - +--------------------+ - | Translates to the | - | standard Counter | - | sysfs output | - |--------------------| - | Type: const char * | - | Value: "42" | - +--------------------+ - | - --------------- - / const char * / - --------------- + --------------- ----------------------- + / const char * / / struct counter_event / + --------------- ----------------------- + | | + | V + | +-----------+ + | | read | + | +-----------+ + | \ Count: 42 / + | ----------- | V +--------------------------------------------------+ @@ -426,7 +420,7 @@ driver is exemplified by the following:: \ Count: "42" / -------------------------------------------------- -There are three primary components involved: +There are four primary components involved: Counter device driver --------------------- @@ -446,3 +440,136 @@ 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 data 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:: + + int counter_push_event(struct counter_device *const counter, const u8 event); + +The event id is specified by the `event` 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:: + + +------------------------+------------------------+ + | Event 0 | Event 1 | + +------------------------+------------------------+ + | * Count 0 | * Signal 0 | + | * Count 1 | * Signal 0 Extension 0 | + | * Signal 3 | * Extension 4 | + | * Count 4 Extension 2 | | + | * Signal 5 Extension 0 | | + +------------------------+------------------------+ + +When `counter_push_event(counter, 1)` is called for example, it will go +down the list for Event 1 and execute the read callbacks for Signal 0, +Signal 0 Extension 0, and Extension 4 -- 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: + +* COUNTER_CLEAR_WATCHES_IOCTL: + Clear all Counter watches from all events + +* COUNTER_SET_WATCH_IOCTL: + Set a Counter watch on the specified event + +To configure events to gather Counter data, users first populate a +`struct counter_watch` with the relevant event id and the information +for the desired Counter component from which to read, and then pass it +via the `COUNTER_SET_WATCH_IOCTL` ioctl command. + +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. + +For example, the following userspace code opens `/dev/counter0`, +configures Event 0 to gather Count 0 and Count 1, and prints out the +data as it becomes available on the character device node:: + + #include + #include + #include + #include + #include + #include + + struct counter_watch watches[2] = { + { + .event = 0, + .component.owner_type = COUNTER_OWNER_TYPE_COUNT, + .component.owner_id = 0, + .component.type = COUNTER_COMPONENT_TYPE_COUNT, + }, + { + .event = 0, + .component.owner_type = COUNTER_OWNER_TYPE_COUNT, + .component.owner_id = 1, + .component.type = COUNTER_COMPONENT_TYPE_COUNT, + }, + }; + + int main(void) + { + struct pollfd pfd = { .events = POLLIN }; + struct counter_event event_data[2]; + + pfd.fd = open("/dev/counter0", O_RDWR); + + ioctl(pfd.fd, COUNTER_SET_WATCH_IOCTL, watches); + ioctl(pfd.fd, COUNTER_SET_WATCH_IOCTL, watches + 1); + + for (;;) { + poll(&pfd, 1, -1); + + read(pfd.fd, event_data, sizeof(event_data)); + + printf("Timestamp 0: %llu\nCount 0: %llu\n" + "Timestamp 1: %llu\nCount 1: %llu\n", + (unsigned long long)event_data[0].timestamp, + (unsigned long long)event_data[0].value_u64, + (unsigned long long)event_data[1].timestamp, + (unsigned long long)event_data[1].value_u64); + } + + return 0; + } diff --git a/Documentation/userspace-api/ioctl/ioctl-number.rst b/Documentation/userspace-api/ioctl/ioctl-number.rst index 59472cd6a11d..63ff377561fd 100644 --- a/Documentation/userspace-api/ioctl/ioctl-number.rst +++ b/Documentation/userspace-api/ioctl/ioctl-number.rst @@ -88,6 +88,7 @@ Code Seq# Include File Comments 0x20 all drivers/cdrom/cm206.h 0x22 all scsi/sg.h +0x3E 00-0F linux/counter.h '!' 00-1F uapi/linux/seccomp.h '#' 00-3F IEEE 1394 Subsystem Block for the entire subsystem