[PATCH v9 0/4] ECAP support on TI AM62x SoC

[Julien Panis <jpanis@baylibre.com>]

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...

This patchset must be applied on top of the following counter subsystem patchset :
https://lore.kernel.org/all/cover.1663693757.git.william.gray@linaro.org/

Modifications since v8 :
	- Add documentation to private driver structure
	- Add mutex to prevent IO race conditions
	- Stop counter before disabling interrupts in ecap_cnt_capture_disable() function
	- Remove returning of status in ecap_cnt_count_get/set_val() functions
	- Remove unnecessary 'return -EBUSY' in all callbacks
	- Remove unnecessary '.id = 0' in ecap_cnt_counts[]
	- Modify driver info in MAINTAINER file

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

	# Set polarity for each capture event
	echo positive > polarity0
	echo negative > polarity1
	echo positive > polarity2
	echo negative > 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 (4):
  dt-bindings: counter: add ti,am62-ecap-capture.yaml
  Documentation: ABI: sysfs-bus-counter: add frequency & num_overflows
    items
  counter: ti-ecap-capture: capture driver support for ECAP
  MAINTAINERS: add TI ECAP driver info

 Documentation/ABI/testing/sysfs-bus-counter   |  14 +
 .../counter/ti,am62-ecap-capture.yaml         |  61 ++
 MAINTAINERS                                   |   9 +
 drivers/counter/Kconfig                       |  15 +
 drivers/counter/Makefile                      |   1 +
 drivers/counter/ti-ecap-capture.c             | 614 ++++++++++++++++++
 6 files changed, 714 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/counter/ti,am62-ecap-capture.yaml
 create mode 100644 drivers/counter/ti-ecap-capture.c

-- 
2.37.3