[PATCH v3 0/4] Implement support for Counter array components

[William Breathitt Gray <william.gray@linaro.org>]

Changes in v3:
 - Fix array length overwrite by allocating space for each array element
 - Add support for counter array component reads from Counter chrdev

The COUNTER_COMP_ARRAY Counter component type is introduced to enable
support for Counter array components. With Counter array components,
exposure for buffers on counter devices can be defined via new Counter
array component macros. This should simplify code for driver authors who
would otherwise need to define individual Counter components for each
array element.

Driver authors can handle reads/writes for an array component by
receiving an element index via the `idx` parameter and processing the
respective value via the `val` parameter.

For example, suppose a driver wants to expose a Count's read-only
capture buffer of four elements using a callback
`foobar_capture_read()`::

        DEFINE_COUNTER_ARRAY(foobar_capture_array, COUNTER_COMP_U64,
                             NULL, 4)
        COUNTER_COMP_COUNT_ARRAY_U64("capture", foobar_capture_read,
                                     NULL, foobar_capture_array)

Respective sysfs attributes for each array element would appear for the
respective Count:

* /sys/bus/counter/devices/counterX/countY/capture0
* /sys/bus/counter/devices/counterX/countY/capture1
* /sys/bus/counter/devices/counterX/countY/capture2
* /sys/bus/counter/devices/counterX/countY/capture3

If a user tries to read _capture2_ for example, `idx` will be `2` when
passed to the `foobar_capture_read()` callback, and thus the driver
knows which array element to handle.

In addition, this patchset introduces the Signal polarity component,
which represents the active level of a respective Signal. There are two
possible states: positive (rising edge) and negative (falling edge). The
104-quad-8 driver is updated to expose its index_polarity functionality
via this new polarity component.

A macro COUNTER_COMP_ARRAY_POLARITY() is provided for driver authors to
support Counter arrays of Signal polarity component type;
DEFINE_COUNTER_AVAILABLE may be used to define the polarity modes that
are passed to DEFINE_COUNTER_ARRAY. The only component types supported
for Counter arrays currently are COUNTER_COMP_U64 and
COUNTER_COMP_SIGNAL_POLARITY.

William Breathitt Gray (4):
  counter: Introduce the Signal polarity component
  counter: 104-quad-8: Add Signal polarity component
  counter: Consolidate Counter extension sysfs attribute creation
  counter: Introduce the COUNTER_COMP_ARRAY component type

 Documentation/ABI/testing/sysfs-bus-counter |  13 +
 drivers/counter/104-quad-8.c                |  35 +++
 drivers/counter/counter-chrdev.c            |  47 ++-
 drivers/counter/counter-sysfs.c             | 303 ++++++++++++++++----
 include/linux/counter.h                     | 131 +++++++++
 include/uapi/linux/counter.h                |   6 +
 6 files changed, 483 insertions(+), 52 deletions(-)


base-commit: a12224997bec72d231a8dd642876e6364decdc45
-- 
2.37.3