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    SubjectRe: [PATCH v6 2/9] counter: Documentation: Add Generic Counter sysfs documentation
    On Wed, 16 May 2018 13:50:55 -0400
    William Breathitt Gray <vilhelm.gray@gmail.com> wrote:

    > This patch adds standard documentation for the userspace sysfs
    > attributes of the Generic Counter interface.
    >
    > Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>

    Some really minor stuff inline. No functional changes.

    Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

    > ---
    > Documentation/ABI/testing/sysfs-bus-counter | 241 ++++++++++++++++++++
    > MAINTAINERS | 1 +
    > 2 files changed, 242 insertions(+)
    > create mode 100644 Documentation/ABI/testing/sysfs-bus-counter
    >
    > diff --git a/Documentation/ABI/testing/sysfs-bus-counter b/Documentation/ABI/testing/sysfs-bus-counter
    > new file mode 100644
    > index 000000000000..e4a45d231b4f
    > --- /dev/null
    > +++ b/Documentation/ABI/testing/sysfs-bus-counter
    > @@ -0,0 +1,241 @@
    > +What: /sys/bus/counter/devices/counterX/countY/count
    > +KernelVersion: 4.18
    > +Contact: linux-iio@vger.kernel.org
    > +Description:
    > + Count data of Count Y represented as a string.
    > +
    > +What: /sys/bus/counter/devices/counterX/countY/ceiling
    > +KernelVersion: 4.18
    > +Contact: linux-iio@vger.kernel.org
    > +Description:
    > + Count value ceiling for Count Y. This is the upper limit for the
    > + respective counter.
    > +
    > +What: /sys/bus/counter/devices/counterX/countY/floor
    > +KernelVersion: 4.18
    > +Contact: linux-iio@vger.kernel.org
    > +Description:
    > + Count value floor for Count Y. This is the lower limit for the
    > + respective counter.
    > +
    > +What: /sys/bus/counter/devices/counterX/countY/count_mode
    > +KernelVersion: 4.18
    > +Contact: linux-iio@vger.kernel.org
    > +Description:
    > + Count mode for channel Y. The ceiling and floor values for
    > + Count Y are used by the count mode where required. The following
    > + count modes are available:
    > +
    > + Normal:
    > + Counting is continuous in either direction.
    > +
    > + Range Limit:
    > + An upper or lower limit is set, mimicking limit switches
    > + in the mechanical counterpart. The upper limit is set to
    > + the Count Y ceiling value, while the lower limit is set
    > + to the Count Y floor value. The counter freezes at
    > + count = ceiling when counting up, and at count = floor
    > + when counting down. At either of these limits, the
    > + counting is resumed only when the count direction is
    > + reversed.
    > +
    > + Non-Recycle:
    > + The counter is disabled whenever a counter overflow or
    > + underflow takes place. The counter is re-enabled when a
    > + new count value is loaded to the counter via a preset
    > + operation or direct write.
    > +
    > + Modulo-N:
    > + A count value boundary is set between the Count Y floor
    > + value and the Count Y ceiling value. The counter is
    > + reset to the Cunt Y floor value at count = ceiling when
    > + counting up, while the counter is set to the Count Y
    > + ceiling value at count = floor when counting down; the
    > + counter does not freeze at the boundary points, but
    > + counts continuously throughout.
    > +
    > +What: /sys/bus/counter/devices/counterX/countY/count_mode_available
    > +What: /sys/bus/counter/devices/counterX/countY/error_noise_available
    > +What: /sys/bus/counter/devices/counterX/countY/function_available
    > +What: /sys/bus/counter/devices/counterX/countY/signalZ_action_available
    > +KernelVersion: 4.18
    > +Contact: linux-iio@vger.kernel.org
    > +Description:
    > + Discrete set of available values for the respective Count Y
    > + configuration are listed in this file. Values are delineated by
    > + newline characters.
    > +
    > +What: /sys/bus/counter/devices/counterX/countY/direction
    > +KernelVersion: 4.18
    > +Contact: linux-iio@vger.kernel.org
    > +Description:
    > + Read-only attribute that indicates the count direction of Count
    > + Y. Two count directions are available: forward and backward.
    > +
    > + Some counter devices are able to determine the direction of
    > + their counting. For example, quadrature encoding counters can
    > + determine the direction of movement by evaluating the leading
    > + phase of the respective A and B quadrature encoding signals.
    > + This attribute exposes such count directions.
    > +
    > +What: /sys/bus/counter/devices/counterX/countY/enable
    > +KernelVersion: 4.18
    > +Contact: linux-iio@vger.kernel.org
    > +Description:
    > + Whether channel Y counter is enabled. Valid attribute values are
    > + boolean.
    > +
    > + This attribute is intended to serve as a pause/unpause mechanism
    > + for Count Y. Suppose a counter device is used to count the total
    > + movement of a conveyor belt: this attribute allows an operator
    > + to temporarily pause the counter, service the conveyor belt,
    > + and then finally unpause the counter to continue where it had
    > + left off.
    > +
    > +What: /sys/bus/counter/devices/counterX/countY/error_noise
    > +KernelVersion: 4.18
    > +Contact: linux-iio@vger.kernel.org
    > +Description:
    > + Read-only attribute that indicates whether excessive noise is
    > + present at the channel Y counter inputs.
    > +
    > +What: /sys/bus/counter/devices/counterX/countY/function
    > +KernelVersion: 4.18
    > +Contact: linux-iio@vger.kernel.org
    > +Description:
    > + Count function mode of Count Y; count function evaluation is
    > + triggered by conditions specified by the Count Y signalZ_action
    > + attributes. The following count functions are available:
    > +
    > + Increase:
    > + Accumulated count is incremented.
    > +
    > + Decrease:
    > + Accumulated count is decremented.
    > +
    > + Pulse-Direction:
    > + Rising edges on quadrature pair signal A updates the
    > + respective count. The input level of quadrature pair
    > + signal B determines direction.
    > +
    > + Quadrature x1 A:
    > + If direction is forward, rising edges on quadrature pair
    > + signal A updates the respective count; if the direction
    > + is backward, falling edges on quadrature pair signal A
    > + updates the respective count. Quadrature encoding
    > + determines the direction.
    > +
    > + Quadrature x1 B:
    > + If direction is forward, rising edges on quadrature pair
    > + signal B updates the respective count; if the direction
    > + is backward, falling edges on quadrature pair signal B
    > + updates the respective count. Quadrature encoding
    > + determines the direction.
    > +
    > + Quadrature x2 A:
    > + Any state transition on quadrature pair signal A updates
    > + the respective count. Quadrature encoding determines the
    > + direction.
    > +
    > + Quadrature x2 B:
    > + Any state transition on quadrature pair signal B updates
    > + the respective count. Quadrature encoding determines the
    > + direction.
    > +
    > + Quadrature x2 Rising:
    > + Rising edges on either quadrature pair signals updates
    > + the respective count. Quadrature encoding determines the
    > + direction.
    > +
    > + Quadrature x2 Falling:
    > + Falling edges on either quadrature pair signals updates
    > + the respective count. Quadrature encoding determines the
    > + direction.
    > +
    > + Quadrature x4:
    > + Any state transition on either quadrature pair signals
    > + updates the respective count. Quadrature encoding
    > + determines the direction.
    > +
    > +What: /sys/bus/counter/devices/counterX/countY/name
    > +KernelVersion: 4.18
    > +Contact: linux-iio@vger.kernel.org
    > +Description:
    > + Read-only attribute that indicates the device-specific name of
    > + Count Y. If possible, this should match the name of the
    > + respective channel as it appears in the device datasheet
    > + documentation text.
    > +
    > +What: /sys/bus/counter/devices/counterX/countY/preset
    > +KernelVersion: 4.18
    > +Contact: linux-iio@vger.kernel.org
    > +Description:
    > + If the counter device supports preset registers, the preset
    > + count for channel Y is provided by this attribute.

    I would add a small block of text here saying what a "preset" typically is.
    It is a term heavily used in encoders etc, but perhaps not some other types
    of counter.

    > +
    > +What: /sys/bus/counter/devices/counterX/countY/preset_enable
    > +KernelVersion: 4.18
    > +Contact: linux-iio@vger.kernel.org
    > +Description:
    > + Whether channel Y counter preset operation is enabled. Valid
    > + attribute values are boolean.
    > +
    > +What: /sys/bus/counter/devices/counterX/countY/signalZ_action
    > +KernelVersion: 4.18
    > +Contact: linux-iio@vger.kernel.org
    > +Description:
    > + Action mode of Count Y for Signal Z. This attribute indicates
    > + the condition of Signal Z that triggers the count function
    > + evaluation for Count Y. The following action modes are
    > + available:
    > +
    > + None:
    > + Signal does not trigger the count function. In
    > + Pulse-Direction count function mode, this Signal is
    > + evaluated as Direction.
    > +
    > + Rising Edge:
    > + Low state transitions to high state.
    > +
    > + Falling Edge:
    > + High state transitions to low state.
    > +
    > + Both Edges:
    > + Any state transition.
    > +
    > +What: /sys/bus/counter/devices/counterX/name
    > +KernelVersion: 4.18
    > +Contact: linux-iio@vger.kernel.org
    > +Description:
    > + Read-only attribute that indicates the device-specific name of
    > + the Counter. This should match the name of the device as it
    > + appears in its respective datasheet documentation text.

    As below, I'm not sure if "documentation text" makes it clearer or less clear..

    > +
    > +What: /sys/bus/counter/devices/counterX/num_counts
    > +KernelVersion: 4.18
    > +Contact: linux-iio@vger.kernel.org
    > +Description:
    > + Read-only attribute that indicates the total number of Counts
    > + belonging to the Counter.
    > +
    > +What: /sys/bus/counter/devices/counterX/num_signals
    > +KernelVersion: 4.18
    > +Contact: linux-iio@vger.kernel.org
    > +Description:
    > + Read-only attribute that indicates the total number of Signals
    > + belonging to the Counter.
    > +
    > +What: /sys/bus/counter/devices/counterX/signalY/signal
    > +KernelVersion: 4.18
    > +Contact: linux-iio@vger.kernel.org
    > +Description:
    > + Signal data of Signal Y represented as a string.
    > +
    > +What: /sys/bus/counter/devices/counterX/signalY/name
    > +KernelVersion: 4.18
    > +Contact: linux-iio@vger.kernel.org
    > +Description:
    > + Read-only attribute that indicates the device-specific name of
    > + Signal Y. If possible, this should match the name of the
    > + respective signal as it appears in the device datasheet
    > + documentation text.

    Not sure "documentation text" adds any clarity over the simply "device datasheet"

    > diff --git a/MAINTAINERS b/MAINTAINERS
    > index 2a016d73ab72..1413e3eb49e5 100644
    > --- a/MAINTAINERS
    > +++ b/MAINTAINERS
    > @@ -3673,6 +3673,7 @@ COUNTER SUBSYSTEM
    > M: William Breathitt Gray <vilhelm.gray@gmail.com>
    > L: linux-iio@vger.kernel.org
    > S: Maintained
    > +F: Documentation/ABI/testing/sysfs-bus-counter*
    > F: drivers/counter/
    > F: include/linux/counter.h
    >

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