linux-kernel - [RFC PATCH 0/3] pwm: add support for duty

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Date: Thu,  4 Apr 2024 20:30:22 -0400
From: Trevor Gamblin <tgamblin@...libre.com>
To: linux-pwm@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	u.kleine-koenig@...gutronix.de,
	michael.hennerich@...log.com,
	nuno.sa@...log.com,
	tgamblin@...libre.com,
	dlechner@...libre.com
Subject: [RFC PATCH 0/3] pwm: add support for duty_offset

This series extends the PWM subsystem to support the duty_offset feature
found on some PWM devices. It includes a patch to enable this feature
for the axi-pwmgen driver, which can also serve as an example of how to
implement it for other devices. It also contains a patch adding a new
pwm_config_full() function mirroring the behavior of pwm_config() but
with duty_offset included, to help maintain compatibility for drivers
that don't support the feature.

The series was tested on actual hardware using a Zedboard. An
oscilloscope was used to validate that the generated PWM signals matched
the requested ones. The libpwm [1] tool was also used for testing the
char device functionality.

The series is marked RFC as there are some outstanding questions about
implementation:

1. In drivers/pwm/core.c, __pwm_apply() was modified to check that the
sum of state->duty_offset + state->duty_cycle does not exceed
state->period, but in the character device section these values are
being checked separately. Is this intentional? What is the intended
behavior?

2. Should __pwm_apply() explicitly disallow PWM_POLARITY_INVERSED and
duty_offset together?

3. Are there other places that would need duty_offset handling which
have been missed?

Note that in addition to the other patches in this series, the changes
to the axi-pwmgen driver rely on [2] and [3], which haven't been picked
up yet.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/ukleinek/libpwm.git/
[2] https://lore.kernel.org/linux-pwm/20240301173343.1086332-1-tgamblin@baylibre.com/
[3] https://lore.kernel.org/linux-pwm/20240314204722.1291993-1-tgamblin@baylibre.com/

Trevor Gamblin (3):
  pwm: add duty offset support
  pwm: axi-pwmgen: add duty offset support
  pwm: add pwm_config_full to pwm.h

 drivers/pwm/core.c           | 75 +++++++++++++++++++++++++++++++++---
 drivers/pwm/pwm-axi-pwmgen.c | 35 +++++++++++++----
 include/linux/pwm.h          | 52 ++++++++++++++++++++++---
 include/trace/events/pwm.h   |  6 ++-
 4 files changed, 147 insertions(+), 21 deletions(-)

-- 
2.44.0