linux-kernel - [PATCH v2 0/2] ECAP support on TI AM62x SoC

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Date:   Thu, 28 Jul 2022 14:52:10 +0200
From:   Julien Panis <jpanis@...libre.com>
To:     jic23@...nel.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org
Cc:     lars@...afoo.de, linux-iio@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        mranostay@...com, Julien Panis <jpanis@...libre.com>
Subject: [PATCH v2 0/2] ECAP support on TI AM62x SoC

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. Moreover, input signal can be prescaled.

This driver leverages IIO subsystem to :
- select edge polarity for all 4 capture events (event mode)
- log both event index and timestamp for each capture event
Event polarity, event indexes, and 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 v1:
	- Fix yaml issues (id and example)
	- Use regmap instead of writel/readl
	- Enable/Disable clock explicitly
	- Simplify power management (suspend/resume)
	- Remove unnecessary using of ev_mode variable

Userspace commands :
	cd /sys/devices/platform/bus@...00/23120000.capture/iio\:device2/

	# Configure/Enable data buffers
	echo 1 > scan_elements/in_index_en
	echo 1 > scan_elements/in_timestamp_en
	echo 100 > buffer/length
	echo 1 > buffer/enable

	# Set event mode in range [0 ; 15]
	# One bit for each CAPx register : 1 = falling edge / 0 = rising edge
	# e.g. mode = 13 = 0xd = 0b1101
	# -> falling edge for CAP1-3-4 / rising edge for CAP2
	echo 13 > events/change_falling_value

	# Run ECAP
	echo 1 > en

	# Get the number of available data
	cat buffer/data_available

	# Read data
	hexdump -v /dev/iio\:device2

	# Stop ECAP
	echo 0 > en

Julien Panis (2):
  dt-binding: iio: time: add capture-tiecap.yaml
  iio: time: capture-tiecap: capture driver support for ECAP

 .../bindings/iio/time/capture-tiecap.yaml     |  68 +++
 drivers/iio/Kconfig                           |   1 +
 drivers/iio/Makefile                          |   1 +
 drivers/iio/time/Kconfig                      |  22 +
 drivers/iio/time/Makefile                     |   6 +
 drivers/iio/time/capture-tiecap.c             | 521 ++++++++++++++++++
 6 files changed, 619 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/time/capture-tiecap.yaml
 create mode 100644 drivers/iio/time/Kconfig
 create mode 100644 drivers/iio/time/Makefile
 create mode 100644 drivers/iio/time/capture-tiecap.c

-- 
2.25.1