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[72.189.64.225]) by smtp.gmail.com with ESMTPSA id b14sm18349966qtx.36.2020.12.25.16.15.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 25 Dec 2020 16:15:48 -0800 (PST) From: William Breathitt Gray To: jic23@kernel.org Subject: [PATCH v7 4/5] docs: counter: Document character device interface Date: Fri, 25 Dec 2020 19:15:37 -0500 Message-Id: <1e69b7beae4cf352bddb379220d0d52b20db0634.1608935587.git.vilhelm.gray@gmail.com> X-Mailer: git-send-email 2.29.2 In-Reply-To: References: MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201225_191551_515836_65F64F9A X-CRM114-Status: GOOD ( 24.41 ) 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, 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 This patch adds high-level documentation about the Counter subsystem character device interface. Signed-off-by: William Breathitt Gray --- Documentation/ABI/testing/sysfs-bus-counter | 9 + Documentation/driver-api/generic-counter.rst | 236 +++++++++++++++--- .../userspace-api/ioctl/ioctl-number.rst | 1 + 3 files changed, 205 insertions(+), 41 deletions(-) diff --git a/Documentation/ABI/testing/sysfs-bus-counter b/Documentation/ABI/testing/sysfs-bus-counter index 1820ce2f9183..8f6ea0a50b75 100644 --- a/Documentation/ABI/testing/sysfs-bus-counter +++ b/Documentation/ABI/testing/sysfs-bus-counter @@ -99,6 +99,15 @@ Description: Read-only attribute that indicates whether excessive noise is present at the channel Y counter inputs. +What: /sys/bus/counter/devices/counterX/countY/extensionZ_name +What: /sys/bus/counter/devices/counterX/extensionZ_name +What: /sys/bus/counter/devices/counterX/signalY/extensionZ_name +KernelVersion: 5.12 +Contact: linux-iio@vger.kernel.org +Description: + Read-only attribute that indicates the component name of + Extension Z. + What: /sys/bus/counter/devices/counterX/countY/function KernelVersion: 5.2 Contact: linux-iio@vger.kernel.org diff --git a/Documentation/driver-api/generic-counter.rst b/Documentation/driver-api/generic-counter.rst index b842ddbbd8a0..4775dcaff557 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 ========== @@ -387,16 +374,16 @@ userspace interface components:: / driver callbacks / ------------------- | - +---------------+ - | - V - +--------------------+ - | Counter sysfs | - +--------------------+ - | Translates to the | - | standard Counter | - | sysfs output | - +--------------------+ + +---------------+---------------+ + | | + 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:: @@ -427,23 +414,30 @@ driver and Counter userspace interface:: / u64 / ---------- | - +---------------+ - | - V - +--------------------+ - | Counter sysfs | - +--------------------+ - | Translates to the | - | standard Counter | - | sysfs output | - |--------------------| - | Type: const char * | - | Value: "42" | - +--------------------+ - | - --------------- - / const char * / - --------------- + +---------------+---------------+ + | | + 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 +--------------------------------------------------+ @@ -452,7 +446,7 @@ driver and Counter userspace interface:: \ Count: "42" / -------------------------------------------------- -There are three primary components involved: +There are four primary components involved: Counter device driver --------------------- @@ -472,3 +466,163 @@ 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, + 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 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_ADD_WATCH_IOCTL: + Add a Counter watch for the specified event + +* COUNTER_LOAD_WATCHES_IOCTL: + Activates the Counter watches added earlier + +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_LOAD_WATCHES_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. + +For example, the following userspace code opens `/dev/counter0`, +configures the `COUNTER_EVENT_INDEX` event channel 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] = { + { + .component.type = COUNTER_COMPONENT_COUNT, + .component.scope = COUNTER_SCOPE_COUNT, + .component.parent = 0, + .event = COUNTER_EVENT_INDEX, + .channel = 0, + }, + { + .component.type = COUNTER_COMPONENT_COUNT, + .component.scope = COUNTER_SCOPE_COUNT, + .component.parent = 1, + .event = COUNTER_EVENT_INDEX, + .channel = 0, + }, + }; + + int main(void) + { + int fd; + struct counter_event event_data[2]; + + fd = open("/dev/counter0", O_RDWR); + + ioctl(fd, COUNTER_ADD_WATCH_IOCTL, watches); + ioctl(fd, COUNTER_ADD_WATCH_IOCTL, watches + 1); + ioctl(fd, COUNTER_LOAD_WATCHES_IOCTL); + + for (;;) { + read(fd, event_data, sizeof(event_data)); + + printf("Timestamp 0: %llu\tCount 0: %llu\n" + "Error Message 0: %s\n" + "Timestamp 1: %llu\tCount 1: %llu\n" + "Error Message 1: %s\n", + (unsigned long long)event_data[0].timestamp, + (unsigned long long)event_data[0].value, + strerror(event_data[0].errno), + (unsigned long long)event_data[1].timestamp, + (unsigned long long)event_data[1].value, + strerror(event_data[1].errno)); + } + + return 0; + } diff --git a/Documentation/userspace-api/ioctl/ioctl-number.rst b/Documentation/userspace-api/ioctl/ioctl-number.rst index 55a2d9b2ce33..b7761ceb82a7 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