diff mbox series

[v15,07/13] docs: counter: Document character device interface

Message ID a6f7be32b8ff7cc1e8e416599820a30fa9aab9f5.1628511445.git.vilhelm.gray@gmail.com (mailing list archive)
State New, archived
Headers show
Series Introduce the Counter character device interface | expand

Commit Message

William Breathitt Gray Aug. 9, 2021, 12:37 p.m. UTC
This patch adds high-level documentation about the Counter subsystem
character device interface.

Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
---
 Documentation/driver-api/generic-counter.rst  | 177 ++++++++++++++----
 .../userspace-api/ioctl/ioctl-number.rst      |   1 +
 2 files changed, 137 insertions(+), 41 deletions(-)

Comments

Jonathan Cameron Aug. 15, 2021, 4:51 p.m. UTC | #1
On Mon,  9 Aug 2021 21:37:32 +0900
William Breathitt Gray <vilhelm.gray@gmail.com> wrote:

> This patch adds high-level documentation about the Counter subsystem
> character device interface.
> 
> Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>

Hi William,

Trivial probable typo inline.

I'm struggling somewhat with these interfaces because I simply don't know
enough about how people use counters to know whether they provide everything
people will want. They feel similar to the event handling type functions you
can set up in motor drives, so they may well make sense, but ideally
we need review from someone (other than yourself!) who actually uses this
stuff on a regular basis.

If we don't get any additional review I guess we go ahead anyway
next cycle.

Jonathan

> ---

> +
> +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

Count 7?

> +kfifo as a ``struct counter_event``, which userspace can retrieve via a
> +standard read operation on the respective character device node.
> +

>                                                                       Block for the entire subsystem
William Breathitt Gray Aug. 21, 2021, 10:52 a.m. UTC | #2
On Sun, Aug 15, 2021 at 05:51:02PM +0100, Jonathan Cameron wrote:
> On Mon,  9 Aug 2021 21:37:32 +0900
> William Breathitt Gray <vilhelm.gray@gmail.com> wrote:
> 
> > This patch adds high-level documentation about the Counter subsystem
> > character device interface.
> > 
> > Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
> 
> Hi William,
> 
> Trivial probable typo inline.
> 
> I'm struggling somewhat with these interfaces because I simply don't know
> enough about how people use counters to know whether they provide everything
> people will want. They feel similar to the event handling type functions you
> can set up in motor drives, so they may well make sense, but ideally
> we need review from someone (other than yourself!) who actually uses this
> stuff on a regular basis.
> 
> If we don't get any additional review I guess we go ahead anyway
> next cycle.
> 
> Jonathan
> 
> > ---
> 
> > +
> > +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
> 
> Count 7?

Looks like my finger slipped on my numpad and hit 4 when I intended 7.
I'll fix this for v16, thanks.

William Breathitt Gray
Akira Yokosawa Aug. 22, 2021, 2:03 a.m. UTC | #3
(dropped most CCs)

Hello William,

I spotted a minor error while browsing documentation updates.

On Sat, 21 Aug 2021 19:52:27 +0900, William Breathitt Gray wrote:
> On Sun, Aug 15, 2021 at 05:51:02PM +0100, Jonathan Cameron wrote:
>> On Mon,  9 Aug 2021 21:37:32 +0900
>> William Breathitt Gray <vilhelm.gray@gmail.com> wrote:
...
>> > +
>> > +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:
>> > +
>> > +        +-------------------------------------------------+

This needs to be:

              +------------------------+------------------------+

, so that the table structure can be properly recognized by Sphinx
(kernel-doc tool).

        Thanks, Akira

>> > +        | 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              |
>> > +        +------------------------+------------------------+
>> > +
diff mbox series

Patch

diff --git a/Documentation/driver-api/generic-counter.rst b/Documentation/driver-api/generic-counter.rst
index f6397218aa4c..e9cb95c1c828 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
 ==========
 
@@ -388,16 +375,16 @@  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::
@@ -428,23 +415,30 @@  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
         +--------------------------------------------------+
@@ -453,7 +447,7 @@  driver and Counter userspace interface::
         \ Count: "42"                                      /
          --------------------------------------------------
 
-There are three primary components involved:
+There are four primary components involved:
 
 Counter device driver
 ---------------------
@@ -473,3 +467,104 @@  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::
+
+        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:
+
+        +-------------------------------------------------+
+        | 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:
+
+* :c:macro:`COUNTER_ADD_WATCH_IOCTL`
+
+* :c:macro:`COUNTER_ENABLE_EVENTS_IOCTL`
+
+* :c:macro:`COUNTER_DISABLE_EVENTS_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.
+
+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.
diff --git a/Documentation/userspace-api/ioctl/ioctl-number.rst b/Documentation/userspace-api/ioctl/ioctl-number.rst
index 1409e40e6345..fc4ccc79b1b8 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
                                                                      <http://infiniband.sourceforge.net/>
 0x20  all    drivers/cdrom/cm206.h
 0x22  all    scsi/sg.h
+0x3E  00-0F  linux/counter.h                                         <mailto:linux-iio@vger.kernel.org>
 '!'   00-1F  uapi/linux/seccomp.h
 '#'   00-3F                                                          IEEE 1394 Subsystem
                                                                      Block for the entire subsystem