docs: pwm: Adapt Locking paragraph to reality

We have the distinction between pwm_apply_atomic() and
pwm_apply_might_sleep() since commit c748a6d (pwm: Rename
pwm_apply_state() to pwm_apply_might_sleep()) contained in v6.8-rc1.

Locking in the core was introduced in commit 1cc2e1f ("pwm: Add
more locking", contained in v6.13-rc1) to serialize per-chip callbacks
and device removal.

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

Author: ukleinek

Documentation/driver-api/pwm.rst

@@ -173,10 +173,15 @@ Locking
 -------
 
 The PWM core list manipulations are protected by a mutex, so pwm_get()
-and pwm_put() may not be called from an atomic context. Currently the
-PWM core does not enforce any locking to pwm_enable(), pwm_disable() and
-pwm_config(), so the calling context is currently driver specific. This
-is an issue derived from the former barebone API and should be fixed soon.
+and pwm_put() may not be called from an atomic context.
+Most functions in the PWM consumer API might sleep and so must not be called
+from atomic context. The notable exception is pwm_apply_atomic() which has the
+same semantics as pwm_apply_might_sleep() but can be called from atomic context.
+(The price for that is that it doesn't work for all PWM devices, use
+pwm_might_sleep() to check if a given PWM supports atomic operation.
+
+Locking in the PWM core ensures that callbacks related to a single chip are
+serialized.
 
 Helpers
 -------