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[72.189.64.225]) by smtp.gmail.com with ESMTPSA id j72sm3331351qke.20.2020.07.21.12.36.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Jul 2020 12:36:07 -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 0/5] Introduce the Counter character device interface Date: Tue, 21 Jul 2020 15:35:46 -0400 Message-Id: X-Mailer: git-send-email 2.27.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Changes in v4: - Reimplement character device interface to report Counter events - Implement Counter timestamps - Implement poll() support - Convert microchip-tcb-capture.c to new driver interface - Add IRQ support for the 104-quad-8 Counter driver Over the past couple years we have noticed some shortcomings with the Counter sysfs interface. Although useful in the majority of situations, there are certain use-cases where interacting through sysfs attributes can become cumbersome and inefficient. A desire to support more advanced functionality such as timestamps, multi-axes positioning tables, and other such latency-sensitive applications, has motivated a reevaluation of the Counter subsystem. I believe a character device interface will be helpful for this more niche area of counter device use. To quell any concerns from the offset: this patchset makes no changes to the existing Counter sysfs userspace interface -- existing userspace applications will continue to work with no modifications necessary. I request that driver maintainers please test their applications to verify that this is true, and report any discrepancies if they arise. However, this patchset does contain a major reimplementation of the Counter subsystem core and driver API. A reimplementation was necessary in order to separate the sysfs code from the counter device drivers and internalize it as a dedicated component of the core Counter subsystem module. A minor benefit from all of this is that the sysfs interface is now ensured a certain amount of consistency because the translation is performed outside of individual counter device drivers. Essentially, the reimplementation has enabled counter device drivers to pass and handle data as native C datatypes now rather than the sysfs strings from before. A high-level view of how a count value is passed down from a counter device driver can be exemplified by the following: ---------------------- / Counter device \ +----------------------+ | Count register: 0x28 | +----------------------+ | ----------------- / raw count data / ----------------- | V +----------------------------+ | Counter device driver |----------+ +----------------------------+ | | Processes data from device | ------------------- |----------------------------| / driver callbacks / | Type: u64 | ------------------- | Value: 42 | | +----------------------------+ | | | ---------- | / u64 / | ---------- | | | | 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 | |--------------------| |---------------------+ | 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" / -------------------------------------------------- Counter device data is exposed through standard character device read operations. Device data is gathered when a Counter event is pushed by the respective Counter device driver. Configuration is handled via ioctl operations on the respective Counter character device node. The following are some questions I have about this patchset: 1. Should I support multiple file descriptors for the character device in this introduction patchset? I intend to add support for multiple file descriptors to the Counter character device, but I restricted this patchset to a single file descriptor to simplify the code logic for the sake of review. If there is enough interest, I can add support for multiple file descriptors in the next revision; I anticipate that this should be simple to implement through the allocation of a kfifo for each file descriptor during the open callback. 2. Should struct counter_event have a union for different value types, or just a value u8 array? Currently I expose the event data value via a union containing the various possible Counter data types (value_u8 and value_u64). It is up to the user to select the right union member for the data they received. Would it make sense to return this data in a u8 array instead, with the expectation that the user will cast to the necessary data type? 3. How should errors be returned for Counter data reads performed by Counter events? Counter events are configured with a list of Counter data read operations to perform for the user. Any one of those data reads can return an error code, but not necessarily all of them. Currently, the code exits early when an error code is returned. Should the code instead continue on, saving the error code to the struct counter_event for userspace to handle? William Breathitt Gray (5): counter: Internalize sysfs interface code docs: counter: Update to reflect sysfs internalization counter: Add character device interface docs: counter: Document character device interface counter: 104-quad-8: Add IRQ support for the ACCES 104-QUAD-8 .../ABI/testing/sysfs-bus-counter-104-quad-8 | 32 + Documentation/driver-api/generic-counter.rst | 363 +++- .../userspace-api/ioctl/ioctl-number.rst | 1 + MAINTAINERS | 2 +- drivers/counter/104-quad-8.c | 753 +++++---- drivers/counter/Kconfig | 6 +- drivers/counter/Makefile | 1 + drivers/counter/counter-chrdev.c | 441 +++++ drivers/counter/counter-chrdev.h | 16 + drivers/counter/counter-core.c | 188 +++ drivers/counter/counter-sysfs.c | 849 ++++++++++ drivers/counter/counter-sysfs.h | 14 + drivers/counter/counter.c | 1496 ----------------- drivers/counter/ftm-quaddec.c | 59 +- drivers/counter/microchip-tcb-capture.c | 104 +- drivers/counter/stm32-lptimer-cnt.c | 161 +- drivers/counter/stm32-timer-cnt.c | 139 +- drivers/counter/ti-eqep.c | 211 +-- include/linux/counter.h | 633 +++---- include/linux/counter_enum.h | 45 - include/uapi/linux/counter.h | 90 + 21 files changed, 2919 insertions(+), 2685 deletions(-) create mode 100644 drivers/counter/counter-chrdev.c create mode 100644 drivers/counter/counter-chrdev.h create mode 100644 drivers/counter/counter-core.c create mode 100644 drivers/counter/counter-sysfs.c create mode 100644 drivers/counter/counter-sysfs.h delete mode 100644 drivers/counter/counter.c delete mode 100644 include/linux/counter_enum.h create mode 100644 include/uapi/linux/counter.h -- 2.27.0