linux-toradex.git/Documentation/driver-api/pwm.rst, branch v7.1-rc7

docs: pwm: Adapt Locking paragraph to reality

2025-07-07T06:39:36+00:00

We have the distinction between pwm_apply_atomic() and
pwm_apply_might_sleep() since commit c748a6d77c06 (pwm: Rename
pwm_apply_state() to pwm_apply_might_sleep()) contained in v6.8-rc1.

Locking in the core was introduced in commit 1cc2e1faafb3 ("pwm: Add
more locking", contained in v6.13-rc1) to serialize per-chip callbacks
and device removal.

Signed-off-by: Uwe Kleine-König 
Link: https://lore.kernel.org/r/20250624100500.1429163-2-u.kleine-koenig@baylibre.com
Signed-off-by: Uwe Kleine-König

pwm: Provide pwmchip_alloc() function and a devm variant of it

2024-02-15T11:59:15+00:00

This function allocates a struct pwm_chip and driver data. Compared to
the status quo the split into pwm_chip and driver data is new, otherwise
it doesn't change anything relevant (yet).

The intention is that after all drivers are switched to use this
allocation function, its possible to add a struct device to struct
pwm_chip to properly track the latter's lifetime without touching all
drivers again. Proper lifetime tracking is a necessary precondition to
introduce character device support for PWMs (that implements atomic
setting and doesn't suffer from the sysfs overhead of the /sys/class/pwm
userspace support).

The new function pwmchip_priv() (obviously?) only works for chips
allocated with pwmchip_alloc().

Link: https://lore.kernel.org/r/9577d6053a5a52536057dc8654ff567181c2da82.1707900770.git.u.kleine-koenig@pengutronix.de
Signed-off-by: Uwe Kleine-König

pwm: Make it possible to apply PWM changes in atomic context

2023-12-20T15:07:06+00:00

Some PWM devices require sleeping, for example if the pwm device is
connected over I2C. However, many PWM devices could be used from atomic
context, e.g. memory mapped PWM. This is useful for, for example, the
pwm-ir-tx driver which requires precise timing. Sleeping causes havoc
with the generated IR signal.

Since not all PWM devices can support atomic context, we also add a
pwm_might_sleep() function to check if is not supported.

Signed-off-by: Sean Young 
Reviewed-by: Uwe Kleine-König 
Signed-off-by: Thierry Reding

pwm: Rename pwm_apply_state() to pwm_apply_might_sleep()

2023-12-20T15:07:04+00:00

In order to introduce a pwm api which can be used from atomic context,
we will need two functions for applying pwm changes:

	int pwm_apply_might_sleep(struct pwm *, struct pwm_state *);
	int pwm_apply_atomic(struct pwm *, struct pwm_state *);

This commit just deals with renaming pwm_apply_state(), a following
commit will introduce the pwm_apply_atomic() function.

Acked-by: Uwe Kleine-König 
Acked-by: Guenter Roeck 
Acked-by: Mark Brown 
Acked-by: Dmitry Torokhov  # for input
Acked-by: Hans de Goede 
Acked-by: Jani Nikula 
Acked-by: Lee Jones 
Signed-off-by: Sean Young 
Signed-off-by: Thierry Reding

pwm: Adapt sysfs API documentation to reality

2023-10-10T19:35:54+00:00

Most low-level PWM drivers support duty_cycle == period, and so does the
sysfs API. Also polarity can be changed for enabled PWMs since commit
39100ceea79f ("pwm: Switch to the atomic API").

Reported-by: Jens Gehrlein 
Signed-off-by: Uwe Kleine-König 
Signed-off-by: Jonathan Corbet 
Link: https://lore.kernel.org/r/20230911154454.675057-1-u.kleine-koenig@pengutronix.de

pwm: Delete deprecated functions pwm_request() and pwm_free()

2023-04-13T12:27:53+00:00

Since commit 5a7fbe452ad9 ("backlight: pwm_bl: Drop support for legacy PWM
probing") the last user of pwm_request() and pwm_free() is gone. So remove
these functions that were deprecated over 10 years ago in commit
8138d2ddbcca ("pwm: Add table-based lookup for static mappings").

Signed-off-by: Uwe Kleine-König 
[thierry.reding@gmail.com: clean up a bit after removal]
Signed-off-by: Thierry Reding

pwm: core: Get rid of unused devm_of_pwm_get()

2022-09-19T13:17:05+00:00

The devm_of_pwm_get() has recently lost its single user, drop
the dead API as well.

Note, the new code should use either plain pwm_get() or managed
devm_pwm_get() or devm_fwnode_pwm_get() APIs.

Signed-off-by: Andy Shevchenko 
Acked-by: Uwe Kleine-König 
Link: https://lore.kernel.org/r/20220826172642.16404-2-andriy.shevchenko@linux.intel.com
Signed-off-by: Guenter Roeck

pwm: Document that the pinstate of a disabled PWM isn't reliable

2022-05-20T14:36:07+00:00

Some (most?) drivers emit the inactive state when the PWM is disabled.
However there are exceptions, so document that a consumer better doesn't
depend on this behaviour.

Some known exceptions:

  - imx27 emits 0 independent of the configured polarity
  - mxs just drives the output to the last emitted state.
  - iqs620a makes the output tristated on disable, so an external
    pull-down would be required.

Signed-off-by: Uwe Kleine-König 
Acked-by: Alexander Stein 
Signed-off-by: Thierry Reding

pwm: core: Remove unused devm_pwm_put()

2021-06-30T17:12:19+00:00

There are no users and seems no will come of the devm_pwm_put().
Remove the function.

While at it, slightly update documentation.

Signed-off-by: Andy Shevchenko 
Reviewed-by: Uwe Kleine-König 
Signed-off-by: Thierry Reding

pwm: core: Support new usage_power setting in PWM state

2021-06-04T09:43:52+00:00

If usage_power is set, the PWM driver is only required to maintain
the power output but has more freedom regarding signal form.

If supported, the signal can be optimized, for example to
improve EMI by phase shifting individual channels.

Signed-off-by: Clemens Gruber 
Signed-off-by: Thierry Reding