The Enhanced Capture (ECAP) module can be used to timestamp events
detected on signal input pin. It can be used for time measurements
of pulse train signals.

ECAP module includes 4 timestamp capture registers. For all 4 sequenced
timestamp capture events (0->1->2->3->0->...), edge polarity (falling/rising
edge) can be selected.

This driver leverages counter subsystem to :
- select edge polarity for all 4 capture events (event mode)
- log timestamps for each capture event
Event polarity, and CAP0/1/2/3 timestamps give all the information
about the input pulse train. Further information can easily be computed :
period and/or duty cycle if frequency is constant, elapsed time between
pulses, etc...

Modifications since v5:
	- Fix descriptions for capture items in sysfs-bus-counter ABI file
	- Modify TI_ECAP_CAPTURE help in Kconfig file
	- Replace ecap_event_id enum with defines
	- Add callbacks to reset nb_ovf & TSCNT
	- Modify action_read callback to serve both clock and input signals
	- Modify watch_validate callback
	- Replace 'count_cumul' with 'num_overflows' & 'ceiling' components
	- Replace one-based index with zero-based index for polarityX & captureX
	- Reverse clock & input signal order (0/1)
	- Move the check for overflow outside of the for-loop (in ISR)
	- Push each CAPx event to respective counter event channels (in ISR)

Userspace commands :
	### CLOCK SIGNAL ###
	cd /sys/bus/counter/devices/counter0/signal0

	# Get frequency
	cat frequency

	### INPUT SIGNAL ###
	cd /sys/bus/counter/devices/counter0/signal1

	# Get available polarities for each capture event
	cat polarity0_available
	cat polarity1_available
	cat polarity2_available
	cat polarity3_available

	# Get polarity for each capture event
	cat polarity0
	cat polarity1
	cat polarity2
	cat polarity3

	# Set polarity for each capture event
	echo rising edge > polarity0
	echo falling edge > polarity1
	echo rising edge > polarity2
	echo falling edge > polarity3

	### COUNT ###
	cd /sys/bus/counter/devices/counter0/count0

	# Get ceiling (counter max value)
	cat ceiling

	# Reset number of overflows & current timebase counter value
	echo 0 > num_overflows
	echo 0 > count

	# Run ECAP
	echo 1 > enable

	# Get number of overflows & current timebase counter value
	cat num_overflows
	cat count

	# Get captured timestamps
	cat capture0
	cat capture1
	cat capture2
	cat capture3

	# Note that counter watches can also be used to get
	# data from userspace application
	# -> see tools/counter/counter_example.c

	# Pause ECAP
	echo 0 > enable

Julien Panis (3):
  dt-bindings: counter: add ti,am62-ecap-capture.yaml
  Documentation: ABI: sysfs-bus-counter: add capture items
  counter: ti-ecap-capture: capture driver support for ECAP

 Documentation/ABI/testing/sysfs-bus-counter   |  45 ++
 .../counter/ti,am62-ecap-capture.yaml         |  61 ++
 drivers/counter/Kconfig                       |  15 +
 drivers/counter/Makefile                      |   1 +
 drivers/counter/ti-ecap-capture.c             | 653 ++++++++++++++++++
 include/uapi/linux/counter.h                  |   2 +
 6 files changed, 777 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/counter/ti,am62-ecap-capture.yaml
 create mode 100644 drivers/counter/ti-ecap-capture.c

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2.37.3