pwm: Assume a disabled PWM to emit a constant inactive output

[ Upstream commit b2eaa11 ]

Some PWM hardwares (e.g. MC33XS2410) cannot implement a zero duty cycle
but can instead disable the hardware which also results in a constant
inactive output.

There are some checks (enabled with CONFIG_PWM_DEBUG) to help
implementing a driver without violating the normal rounding rules. Make
them less strict to let above described hardware pass without warning.

Reported-by: Dimitri Fedrau <dima.fedrau@gmail.com>
Link: https://lore.kernel.org/r/20241103205215.GA509903@debian
Fixes: 3ad1f3a ("pwm: Implement some checks for lowlevel drivers")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Reviewed-by: Dimitri Fedrau <dima.fedrau@gmail.com>
Tested-by: Dimitri Fedrau <dima.fedrau@gmail.com>
Link: https://lore.kernel.org/r/20241105153521.1001864-2-u.kleine-koenig@baylibre.com
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: ukleinek

drivers/pwm/core.c

@@ -75,15 +75,19 @@ static void pwm_apply_debug(struct pwm_device *pwm,
 	    state->duty_cycle < state->period)
 		dev_warn(pwmchip_parent(chip), ".apply ignored .polarity\n");
 
-	if (state->enabled &&
+	if (state->enabled && s2.enabled &&
 	    last->polarity == state->polarity &&
 	    last->period > s2.period &&
 	    last->period <= state->period)
 		dev_warn(pwmchip_parent(chip),
 			 ".apply didn't pick the best available period (requested: %llu, applied: %llu, possible: %llu)\n",
 			 state->period, s2.period, last->period);
 
-	if (state->enabled && state->period < s2.period)
+	/*
+	 * Rounding period up is fine only if duty_cycle is 0 then, because a
+	 * flat line doesn't have a characteristic period.
+	 */
+	if (state->enabled && s2.enabled && state->period < s2.period && s2.duty_cycle)
 		dev_warn(pwmchip_parent(chip),
 			 ".apply is supposed to round down period (requested: %llu, applied: %llu)\n",
 			 state->period, s2.period);
@@ -99,7 +103,7 @@ static void pwm_apply_debug(struct pwm_device *pwm,
 			 s2.duty_cycle, s2.period,
 			 last->duty_cycle, last->period);
 
-	if (state->enabled && state->duty_cycle < s2.duty_cycle)
+	if (state->enabled && s2.enabled && state->duty_cycle < s2.duty_cycle)
 		dev_warn(pwmchip_parent(chip),
 			 ".apply is supposed to round down duty_cycle (requested: %llu/%llu, applied: %llu/%llu)\n",
 			 state->duty_cycle, state->period,