On 7/5/21 3:18 AM, William Breathitt Gray wrote:
This patch adds high-level documentation about the Counter subsystem character device interface. Signed-off-by: William Breathitt Gray <vilhelm.gray@xxxxxxxxx> --- Documentation/driver-api/generic-counter.rst | 185 ++++++++++++++---- .../userspace-api/ioctl/ioctl-number.rst | 1 + 2 files changed, 145 insertions(+), 41 deletions(-) diff --git a/Documentation/driver-api/generic-counter.rst b/Documentation/driver-api/generic-counter.rst index f6397218aa4c..62a702e7f994 100644 --- a/Documentation/driver-api/generic-counter.rst +++ b/Documentation/driver-api/generic-counter.rst
+ +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:: + + void 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::
Won't the :: here make this appear as text instead of an HTML table? (might need to change ~~~ to --- [top line] and === [middle line])
+ + +~~~~~~~~~~~~~~~~~~~~~~~~+~~~~~~~~~~~~~~~~~~~~~~~~+ + | 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_ADD_WATCH_IOCTL: + Queues a Counter watch for the specified event. The queued watches + will not be applied until ``COUNTER_ENABLE_EVENTS_IOCTL`` is called. + +* COUNTER_ENABLE_EVENTS_IOCTL: + Enables monitoring the events specified by the Counter watches that + were queued by ``COUNTER_ADD_WATCH_IOCTL``. If events are already + enabled, the new set of watches replaces the old one. Calling this + ioctl also has the effect of clearing the queue of watches added by + ``COUNTER_ADD_WATCH_IOCTL``. + +* COUNTER_DISABLE_EVENTS_IOCTL: + Stops monitoring the previously enabled events.
I wouldn't mind seeing more of this documentation in the actual header file and just referenced here with :c:macro:`COUNTER_ADD_WATCH_IOCTL`
+ +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.
To make sure I am understanding this correctly, scope + parent determines this part of the path: /sys/.../counterX/<scope><parent>/<component> Or in the case that scope == COUNTER_SCOPE_DEVICE then parent is not applicable: /sys/.../counterX/<component> I suggested parent_id instead of parent earlier, but maybe scope_id would be a better name? (Or rename scope to parent_type?)
+ +The ``COUNTER_ADD_WATCH_IOCTL`` command will buffer these Counter +watches. When ready, the ``COUNTER_ENABLE_EVENTS_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.
