pwm: Changes for v4.7-rc1

This set of changes introduces an atomic API to the PWM subsystem. This
 is influenced by the DRM atomic API that was introduced a while back,
 though it is obviously a lot simpler. The fundamental idea remains the
 same, though: drivers provide a single callback to implement the atomic
 configuration of a PWM channel.
 
 As a side-effect the PWM subsystem gains the ability for initial state
 retrieval, so that the logical state mirrors that of the hardware. Many
 use-cases don't care about this, but for others it is essential.
 
 These new features require changes in all users, which these patches
 take care of. The core is transitioned to use the atomic callback if
 available and provides a fallback mechanism for other drivers.
 
 Changes to transition users and drivers to the atomic API are postponed
 to v4.8.
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Merge tag 'pwm/for-4.7-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/thierry.reding/linux-pwm

Pull pwm updates from Thierry Reding:
 "This set of changes introduces an atomic API to the PWM subsystem.
  This is influenced by the DRM atomic API that was introduced a while
  back, though it is obviously a lot simpler.  The fundamental idea
  remains the same, though: drivers provide a single callback to
  implement the atomic configuration of a PWM channel.

  As a side-effect the PWM subsystem gains the ability for initial state
  retrieval, so that the logical state mirrors that of the hardware.
  Many use-cases don't care about this, but for others it is essential.

  These new features require changes in all users, which these patches
  take care of.  The core is transitioned to use the atomic callback if
  available and provides a fallback mechanism for other drivers.

  Changes to transition users and drivers to the atomic API are
  postponed to v4.8"

* tag 'pwm/for-4.7-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/thierry.reding/linux-pwm: (30 commits)
  pwm: Add information about polarity, duty cycle and period to debugfs
  pwm: Switch to the atomic API
  pwm: Update documentation
  pwm: Add core infrastructure to allow atomic updates
  pwm: Add hardware readout infrastructure
  pwm: Move the enabled/disabled info into pwm_state
  pwm: Introduce the pwm_state concept
  pwm: Keep PWM state in sync with hardware state
  ARM: Explicitly apply PWM config extracted from pwm_args
  drm: i915: Explicitly apply PWM config extracted from pwm_args
  input: misc: pwm-beeper: Explicitly apply PWM config extracted from pwm_args
  input: misc: max8997: Explicitly apply PWM config extracted from pwm_args
  backlight: lm3630a: explicitly apply PWM config extracted from pwm_args
  backlight: lp855x: Explicitly apply PWM config extracted from pwm_args
  backlight: lp8788: Explicitly apply PWM config extracted from pwm_args
  backlight: pwm_bl: Use pwm_get_args() where appropriate
  fbdev: ssd1307fb: Use pwm_get_args() where appropriate
  regulator: pwm: Use pwm_get_args() where appropriate
  leds: pwm: Use pwm_get_args() where appropriate
  input: misc: max77693: Use pwm_get_args() where appropriate
  ...

Documentation/pwm.txt

@@ -42,9 +42,26 @@ variants of these functions, devm_pwm_get() and devm_pwm_put(), also exist.
 
 After being requested, a PWM has to be configured using:
 
-int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns);
+int pwm_apply_state(struct pwm_device *pwm, struct pwm_state *state);
 
-To start/stop toggling the PWM output use pwm_enable()/pwm_disable().
+This API controls both the PWM period/duty_cycle config and the
+enable/disable state.
+
+The pwm_config(), pwm_enable() and pwm_disable() functions are just wrappers
+around pwm_apply_state() and should not be used if the user wants to change
+several parameter at once. For example, if you see pwm_config() and
+pwm_{enable,disable}() calls in the same function, this probably means you
+should switch to pwm_apply_state().
+
+The PWM user API also allows one to query the PWM state with pwm_get_state().
+
+In addition to the PWM state, the PWM API also exposes PWM arguments, which
+are the reference PWM config one should use on this PWM.
+PWM arguments are usually platform-specific and allows the PWM user to only
+care about dutycycle relatively to the full period (like, duty = 50% of the
+period). struct pwm_args contains 2 fields (period and polarity) and should
+be used to set the initial PWM config (usually done in the probe function
+of the PWM user). PWM arguments are retrieved with pwm_get_args().
 
 Using PWMs with the sysfs interface
 -----------------------------------
@@ -105,6 +122,15 @@ goes low for the remainder of the period. Conversely, a signal with inversed
 polarity starts low for the duration of the duty cycle and goes high for the
 remainder of the period.
 
+Drivers are encouraged to implement ->apply() instead of the legacy
+->enable(), ->disable() and ->config() methods. Doing that should provide
+atomicity in the PWM config workflow, which is required when the PWM controls
+a critical device (like a regulator).
+
+The implementation of ->get_state() (a method used to retrieve initial PWM
+state) is also encouraged for the same reason: letting the PWM user know
+about the current PWM state would allow him to avoid glitches.
+
 Locking
 -------
 

arch/arm/mach-s3c24xx/mach-rx1950.c

@@ -496,6 +496,12 @@ static int rx1950_backlight_init(struct device *dev)
 		return PTR_ERR(lcd_pwm);
 	}
 
+	/*
+	 * FIXME: pwm_apply_args() should be removed when switching to
+	 * the atomic PWM API.
+	 */
+	pwm_apply_args(lcd_pwm);
+
 	rx1950_lcd_power(1);
 	rx1950_bl_power(1);
 

drivers/clk/clk-pwm.c

@@ -59,6 +59,7 @@ static int clk_pwm_probe(struct platform_device *pdev)
 	struct clk_init_data init;
 	struct clk_pwm *clk_pwm;
 	struct pwm_device *pwm;
+	struct pwm_args pargs;
 	const char *clk_name;
 	struct clk *clk;
 	int ret;
@@ -71,22 +72,28 @@ static int clk_pwm_probe(struct platform_device *pdev)
 	if (IS_ERR(pwm))
 		return PTR_ERR(pwm);
 
-	if (!pwm->period) {
+	pwm_get_args(pwm, &pargs);
+	if (!pargs.period) {
 		dev_err(&pdev->dev, "invalid PWM period\n");
 		return -EINVAL;
 	}
 
 	if (of_property_read_u32(node, "clock-frequency", &clk_pwm->fixed_rate))
-		clk_pwm->fixed_rate = NSEC_PER_SEC / pwm->period;
+		clk_pwm->fixed_rate = NSEC_PER_SEC / pargs.period;
 
-	if (pwm->period != NSEC_PER_SEC / clk_pwm->fixed_rate &&
+	if (pargs.period != NSEC_PER_SEC / clk_pwm->fixed_rate &&
-	    pwm->period != DIV_ROUND_UP(NSEC_PER_SEC, clk_pwm->fixed_rate)) {
+	    pargs.period != DIV_ROUND_UP(NSEC_PER_SEC, clk_pwm->fixed_rate)) {
 		dev_err(&pdev->dev,
 			"clock-frequency does not match PWM period\n");
 		return -EINVAL;
 	}
 
-	ret = pwm_config(pwm, (pwm->period + 1) >> 1, pwm->period);
+	/*
+	 * FIXME: pwm_apply_args() should be removed when switching to the
+	 * atomic PWM API.
+	 */
+	pwm_apply_args(pwm);
+	ret = pwm_config(pwm, (pargs.period + 1) >> 1, pargs.period);
 	if (ret < 0)
 		return ret;
 

drivers/gpu/drm/i915/intel_panel.c

@@ -1638,6 +1638,12 @@ static int pwm_setup_backlight(struct intel_connector *connector,
 		return -ENODEV;
 	}
 
+	/*
+	 * FIXME: pwm_apply_args() should be removed when switching to
+	 * the atomic PWM API.
+	 */
+	pwm_apply_args(panel->backlight.pwm);
+
 	retval = pwm_config(panel->backlight.pwm, CRC_PMIC_PWM_PERIOD_NS,
 			    CRC_PMIC_PWM_PERIOD_NS);
 	if (retval < 0) {

drivers/hwmon/pwm-fan.c

@@ -40,15 +40,18 @@ struct pwm_fan_ctx {
 
 static int  __set_pwm(struct pwm_fan_ctx *ctx, unsigned long pwm)
 {
+	struct pwm_args pargs;
 	unsigned long duty;
 	int ret = 0;
 
+	pwm_get_args(ctx->pwm, &pargs);
+
 	mutex_lock(&ctx->lock);
 	if (ctx->pwm_value == pwm)
 		goto exit_set_pwm_err;
 
-	duty = DIV_ROUND_UP(pwm * (ctx->pwm->period - 1), MAX_PWM);
+	duty = DIV_ROUND_UP(pwm * (pargs.period - 1), MAX_PWM);
-	ret = pwm_config(ctx->pwm, duty, ctx->pwm->period);
+	ret = pwm_config(ctx->pwm, duty, pargs.period);
 	if (ret)
 		goto exit_set_pwm_err;
 
@@ -215,6 +218,7 @@ static int pwm_fan_probe(struct platform_device *pdev)
 {
 	struct thermal_cooling_device *cdev;
 	struct pwm_fan_ctx *ctx;
+	struct pwm_args pargs;
 	struct device *hwmon;
 	int duty_cycle;
 	int ret;
@@ -233,11 +237,19 @@ static int pwm_fan_probe(struct platform_device *pdev)
 
 	platform_set_drvdata(pdev, ctx);
 
+	/*
+	 * FIXME: pwm_apply_args() should be removed when switching to the
+	 * atomic PWM API.
+	 */
+	pwm_apply_args(ctx->pwm);
+
 	/* Set duty cycle to maximum allowed */
-	duty_cycle = ctx->pwm->period - 1;
+	pwm_get_args(ctx->pwm, &pargs);
+
+	duty_cycle = pargs.period - 1;
 	ctx->pwm_value = MAX_PWM;
 
-	ret = pwm_config(ctx->pwm, duty_cycle, ctx->pwm->period);
+	ret = pwm_config(ctx->pwm, duty_cycle, pargs.period);
 	if (ret) {
 		dev_err(&pdev->dev, "Failed to configure PWM\n");
 		return ret;
@@ -303,14 +315,16 @@ static int pwm_fan_suspend(struct device *dev)
 static int pwm_fan_resume(struct device *dev)
 {
 	struct pwm_fan_ctx *ctx = dev_get_drvdata(dev);
+	struct pwm_args pargs;
 	unsigned long duty;
 	int ret;
 
 	if (ctx->pwm_value == 0)
 		return 0;
 
-	duty = DIV_ROUND_UP(ctx->pwm_value * (ctx->pwm->period - 1), MAX_PWM);
+	pwm_get_args(ctx->pwm, &pargs);
-	ret = pwm_config(ctx->pwm, duty, ctx->pwm->period);
+	duty = DIV_ROUND_UP(ctx->pwm_value * (pargs.period - 1), MAX_PWM);
+	ret = pwm_config(ctx->pwm, duty, pargs.period);
 	if (ret)
 		return ret;
 	return pwm_enable(ctx->pwm);

drivers/input/misc/max77693-haptic.c

@@ -70,10 +70,13 @@ struct max77693_haptic {
 
 static int max77693_haptic_set_duty_cycle(struct max77693_haptic *haptic)
 {
-	int delta = (haptic->pwm_dev->period + haptic->pwm_duty) / 2;
+	struct pwm_args pargs;
+	int delta;
 	int error;
 
-	error = pwm_config(haptic->pwm_dev, delta, haptic->pwm_dev->period);
+	pwm_get_args(haptic->pwm_dev, &pargs);
+	delta = (pargs.period + haptic->pwm_duty) / 2;
+	error = pwm_config(haptic->pwm_dev, delta, pargs.period);
 	if (error) {
 		dev_err(haptic->dev, "failed to configure pwm: %d\n", error);
 		return error;
@@ -234,6 +237,7 @@ static int max77693_haptic_play_effect(struct input_dev *dev, void *data,
 				       struct ff_effect *effect)
 {
 	struct max77693_haptic *haptic = input_get_drvdata(dev);
+	struct pwm_args pargs;
 	u64 period_mag_multi;
 
 	haptic->magnitude = effect->u.rumble.strong_magnitude;
@@ -245,7 +249,8 @@ static int max77693_haptic_play_effect(struct input_dev *dev, void *data,
 	 * The formula to convert magnitude to pwm_duty as follows:
 	 * - pwm_duty = (magnitude * pwm_period) / MAX_MAGNITUDE(0xFFFF)
 	 */
-	period_mag_multi = (u64)haptic->pwm_dev->period * haptic->magnitude;
+	pwm_get_args(haptic->pwm_dev, &pargs);
+	period_mag_multi = (u64)pargs.period * haptic->magnitude;
 	haptic->pwm_duty = (unsigned int)(period_mag_multi >>
 						MAX_MAGNITUDE_SHIFT);
 
@@ -329,6 +334,12 @@ static int max77693_haptic_probe(struct platform_device *pdev)
 		return PTR_ERR(haptic->pwm_dev);
 	}
 
+	/*
+	 * FIXME: pwm_apply_args() should be removed when switching to the
+	 * atomic PWM API.
+	 */
+	pwm_apply_args(haptic->pwm_dev);
+
 	haptic->motor_reg = devm_regulator_get(&pdev->dev, "haptic");
 	if (IS_ERR(haptic->motor_reg)) {
 		dev_err(&pdev->dev, "failed to get regulator\n");

drivers/input/misc/max8997_haptic.c

@@ -306,6 +306,12 @@ static int max8997_haptic_probe(struct platform_device *pdev)
 				error);
 			goto err_free_mem;
 		}
+
+		/*
+		 * FIXME: pwm_apply_args() should be removed when switching to
+		 * the atomic PWM API.
+		 */
+		pwm_apply_args(chip->pwm);
 		break;
 
 	default:

drivers/input/misc/pwm-beeper.c

@@ -87,6 +87,12 @@ static int pwm_beeper_probe(struct platform_device *pdev)
 		goto err_free;
 	}
 
+	/*
+	 * FIXME: pwm_apply_args() should be removed when switching to
+	 * the atomic PWM API.
+	 */
+	pwm_apply_args(beeper->pwm);
+
 	beeper->input = input_allocate_device();
 	if (!beeper->input) {
 		dev_err(&pdev->dev, "Failed to allocate input device\n");

drivers/leds/leds-pwm.c

@@ -91,6 +91,7 @@ static int led_pwm_add(struct device *dev, struct led_pwm_priv *priv,
 		       struct led_pwm *led, struct device_node *child)
 {
 	struct led_pwm_data *led_data = &priv->leds[priv->num_leds];
+	struct pwm_args pargs;
 	int ret;
 
 	led_data->active_low = led->active_low;
@@ -117,7 +118,15 @@ static int led_pwm_add(struct device *dev, struct led_pwm_priv *priv,
 	else
 		led_data->cdev.brightness_set_blocking = led_pwm_set_blocking;
 
-	led_data->period = pwm_get_period(led_data->pwm);
+	/*
+	 * FIXME: pwm_apply_args() should be removed when switching to the
+	 * atomic PWM API.
+	 */
+	pwm_apply_args(led_data->pwm);
+
+	pwm_get_args(led_data->pwm, &pargs);
+
+	led_data->period = pargs.period;
 	if (!led_data->period && (led->pwm_period_ns > 0))
 		led_data->period = led->pwm_period_ns;
 

drivers/pwm/core.c

@@ -75,6 +75,7 @@ static void free_pwms(struct pwm_chip *chip)
 
 	for (i = 0; i < chip->npwm; i++) {
 		struct pwm_device *pwm = &chip->pwms[i];
+
 		radix_tree_delete(&pwm_tree, pwm->pwm);
 	}
 
@@ -128,13 +129,6 @@ static int pwm_device_request(struct pwm_device *pwm, const char *label)
 	set_bit(PWMF_REQUESTED, &pwm->flags);
 	pwm->label = label;
 
-	/*
-	 * FIXME: This should be removed once all PWM users properly make use
-	 * of struct pwm_args to initialize the PWM device. As long as this is
-	 * here, the PWM state and hardware state can get out of sync.
-	 */
-	pwm_apply_args(pwm);
-
 	return 0;
 }
 
@@ -233,6 +227,19 @@ void *pwm_get_chip_data(struct pwm_device *pwm)
 }
 EXPORT_SYMBOL_GPL(pwm_get_chip_data);
 
+static bool pwm_ops_check(const struct pwm_ops *ops)
+{
+	/* driver supports legacy, non-atomic operation */
+	if (ops->config && ops->enable && ops->disable)
+		return true;
+
+	/* driver supports atomic operation */
+	if (ops->apply)
+		return true;
+
+	return false;
+}
+
 /**
  * pwmchip_add_with_polarity() - register a new PWM chip
  * @chip: the PWM chip to add
@@ -251,8 +258,10 @@ int pwmchip_add_with_polarity(struct pwm_chip *chip,
 	unsigned int i;
 	int ret;
 
-	if (!chip || !chip->dev || !chip->ops || !chip->ops->config ||
+	if (!chip || !chip->dev || !chip->ops || !chip->npwm)
-	    !chip->ops->enable || !chip->ops->disable || !chip->npwm)
+		return -EINVAL;
+
+	if (!pwm_ops_check(chip->ops))
 		return -EINVAL;
 
 	mutex_lock(&pwm_lock);
@@ -261,7 +270,7 @@ int pwmchip_add_with_polarity(struct pwm_chip *chip,
 	if (ret < 0)
 		goto out;
 
-	chip->pwms = kzalloc(chip->npwm * sizeof(*pwm), GFP_KERNEL);
+	chip->pwms = kcalloc(chip->npwm, sizeof(*pwm), GFP_KERNEL);
 	if (!chip->pwms) {
 		ret = -ENOMEM;
 		goto out;
@@ -275,8 +284,10 @@ int pwmchip_add_with_polarity(struct pwm_chip *chip,
 		pwm->chip = chip;
 		pwm->pwm = chip->base + i;
 		pwm->hwpwm = i;
-		pwm->polarity = polarity;
+		pwm->state.polarity = polarity;
-		mutex_init(&pwm->lock);
+
+		if (chip->ops->get_state)
+			chip->ops->get_state(chip, pwm, &pwm->state);
 
 		radix_tree_insert(&pwm_tree, pwm->pwm, pwm);
 	}
@@ -436,107 +447,138 @@ void pwm_free(struct pwm_device *pwm)
 EXPORT_SYMBOL_GPL(pwm_free);
 
 /**
- * pwm_config() - change a PWM device configuration
+ * pwm_apply_state() - atomically apply a new state to a PWM device
  * @pwm: PWM device
- * @duty_ns: "on" time (in nanoseconds)
+ * @state: new state to apply. This can be adjusted by the PWM driver
- * @period_ns: duration (in nanoseconds) of one cycle
+ *	   if the requested config is not achievable, for example,
- *
+ *	   ->duty_cycle and ->period might be approximated.
- * Returns: 0 on success or a negative error code on failure.
  */
-int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns)
+int pwm_apply_state(struct pwm_device *pwm, struct pwm_state *state)
 {
 	int err;
 
-	if (!pwm || duty_ns < 0 || period_ns <= 0 || duty_ns > period_ns)
-		return -EINVAL;
-
-	err = pwm->chip->ops->config(pwm->chip, pwm, duty_ns, period_ns);
-	if (err)
-		return err;
-
-	pwm->duty_cycle = duty_ns;
-	pwm->period = period_ns;
-
-	return 0;
-}
-EXPORT_SYMBOL_GPL(pwm_config);
-
-/**
- * pwm_set_polarity() - configure the polarity of a PWM signal
- * @pwm: PWM device
- * @polarity: new polarity of the PWM signal
- *
- * Note that the polarity cannot be configured while the PWM device is
- * enabled.
- *
- * Returns: 0 on success or a negative error code on failure.
- */
-int pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity)
-{
-	int err;
-
-	if (!pwm || !pwm->chip->ops)
-		return -EINVAL;
-
-	if (!pwm->chip->ops->set_polarity)
-		return -ENOSYS;
-
-	mutex_lock(&pwm->lock);
-
-	if (pwm_is_enabled(pwm)) {
-		err = -EBUSY;
-		goto unlock;
-	}
-
-	err = pwm->chip->ops->set_polarity(pwm->chip, pwm, polarity);
-	if (err)
-		goto unlock;
-
-	pwm->polarity = polarity;
-
-unlock:
-	mutex_unlock(&pwm->lock);
-	return err;
-}
-EXPORT_SYMBOL_GPL(pwm_set_polarity);
-
-/**
- * pwm_enable() - start a PWM output toggling
- * @pwm: PWM device
- *
- * Returns: 0 on success or a negative error code on failure.
- */
-int pwm_enable(struct pwm_device *pwm)
-{
-	int err = 0;
-
 	if (!pwm)
 		return -EINVAL;
 
-	mutex_lock(&pwm->lock);
+	if (!memcmp(state, &pwm->state, sizeof(*state)))
+		return 0;
 
-	if (!test_and_set_bit(PWMF_ENABLED, &pwm->flags)) {
+	if (pwm->chip->ops->apply) {
-		err = pwm->chip->ops->enable(pwm->chip, pwm);
+		err = pwm->chip->ops->apply(pwm->chip, pwm, state);
 		if (err)
-			clear_bit(PWMF_ENABLED, &pwm->flags);
+			return err;
+
+		pwm->state = *state;
+	} else {
+		/*
+		 * FIXME: restore the initial state in case of error.
+		 */
+		if (state->polarity != pwm->state.polarity) {
+			if (!pwm->chip->ops->set_polarity)
+				return -ENOTSUPP;
+
+			/*
+			 * Changing the polarity of a running PWM is
+			 * only allowed when the PWM driver implements
+			 * ->apply().
+			 */
+			if (pwm->state.enabled) {
+				pwm->chip->ops->disable(pwm->chip, pwm);
+				pwm->state.enabled = false;
 			}
 
-	mutex_unlock(&pwm->lock);
+			err = pwm->chip->ops->set_polarity(pwm->chip, pwm,
-
+							   state->polarity);
+			if (err)
 				return err;
+
+			pwm->state.polarity = state->polarity;
+		}
+
+		if (state->period != pwm->state.period ||
+		    state->duty_cycle != pwm->state.duty_cycle) {
+			err = pwm->chip->ops->config(pwm->chip, pwm,
+						     state->duty_cycle,
+						     state->period);
+			if (err)
+				return err;
+
+			pwm->state.duty_cycle = state->duty_cycle;
+			pwm->state.period = state->period;
+		}
+
+		if (state->enabled != pwm->state.enabled) {
+			if (state->enabled) {
+				err = pwm->chip->ops->enable(pwm->chip, pwm);
+				if (err)
+					return err;
+			} else {
+				pwm->chip->ops->disable(pwm->chip, pwm);
+			}
+
+			pwm->state.enabled = state->enabled;
+		}
+	}
+
+	return 0;
 }
-EXPORT_SYMBOL_GPL(pwm_enable);
+EXPORT_SYMBOL_GPL(pwm_apply_state);
 
 /**
- * pwm_disable() - stop a PWM output toggling
+ * pwm_adjust_config() - adjust the current PWM config to the PWM arguments
  * @pwm: PWM device
+ *
+ * This function will adjust the PWM config to the PWM arguments provided
+ * by the DT or PWM lookup table. This is particularly useful to adapt
+ * the bootloader config to the Linux one.
  */
-void pwm_disable(struct pwm_device *pwm)
+int pwm_adjust_config(struct pwm_device *pwm)
 {
-	if (pwm && test_and_clear_bit(PWMF_ENABLED, &pwm->flags))
+	struct pwm_state state;
-		pwm->chip->ops->disable(pwm->chip, pwm);
+	struct pwm_args pargs;
+
+	pwm_get_args(pwm, &pargs);
+	pwm_get_state(pwm, &state);
+
+	/*
+	 * If the current period is zero it means that either the PWM driver
+	 * does not support initial state retrieval or the PWM has not yet
+	 * been configured.
+	 *
+	 * In either case, we setup the new period and polarity, and assign a
+	 * duty cycle of 0.
+	 */
+	if (!state.period) {
+		state.duty_cycle = 0;
+		state.period = pargs.period;
+		state.polarity = pargs.polarity;
+
+		return pwm_apply_state(pwm, &state);
+	}
+
+	/*
+	 * Adjust the PWM duty cycle/period based on the period value provided
+	 * in PWM args.
+	 */
+	if (pargs.period != state.period) {
+		u64 dutycycle = (u64)state.duty_cycle * pargs.period;
+
+		do_div(dutycycle, state.period);
+		state.duty_cycle = dutycycle;
+		state.period = pargs.period;
+	}
+
+	/*
+	 * If the polarity changed, we should also change the duty cycle.
+	 */
+	if (pargs.polarity != state.polarity) {
+		state.polarity = pargs.polarity;
+		state.duty_cycle = state.period - state.duty_cycle;
+	}
+
+	return pwm_apply_state(pwm, &state);
 }
-EXPORT_SYMBOL_GPL(pwm_disable);
+EXPORT_SYMBOL_GPL(pwm_adjust_config);
 
 static struct pwm_chip *of_node_to_pwmchip(struct device_node *np)
 {
@@ -754,13 +796,13 @@ struct pwm_device *pwm_get(struct device *dev, const char *con_id)
 	if (!chip)
 		goto out;
 
-	pwm->args.period = chosen->period;
-	pwm->args.polarity = chosen->polarity;
-
 	pwm = pwm_request_from_chip(chip, chosen->index, con_id ?: dev_id);
 	if (IS_ERR(pwm))
 		goto out;
 
+	pwm->args.period = chosen->period;
+	pwm->args.polarity = chosen->polarity;
+
 out:
 	mutex_unlock(&pwm_lookup_lock);
 	return pwm;
@@ -907,15 +949,23 @@ static void pwm_dbg_show(struct pwm_chip *chip, struct seq_file *s)
 
 	for (i = 0; i < chip->npwm; i++) {
 		struct pwm_device *pwm = &chip->pwms[i];
+		struct pwm_state state;
+
+		pwm_get_state(pwm, &state);
 
 		seq_printf(s, " pwm-%-3d (%-20.20s):", i, pwm->label);
 
 		if (test_bit(PWMF_REQUESTED, &pwm->flags))
 			seq_puts(s, " requested");
 
-		if (pwm_is_enabled(pwm))
+		if (state.enabled)
 			seq_puts(s, " enabled");
 
+		seq_printf(s, " period: %u ns", state.period);
+		seq_printf(s, " duty: %u ns", state.duty_cycle);
+		seq_printf(s, " polarity: %s",
+			   state.polarity ? "inverse" : "normal");
+
 		seq_puts(s, "\n");
 	}
 }

drivers/pwm/pwm-crc.c

@@ -75,7 +75,7 @@ static int crc_pwm_config(struct pwm_chip *c, struct pwm_device *pwm,
 		return -EINVAL;
 	}
 
-	if (pwm->period != period_ns) {
+	if (pwm_get_period(pwm) != period_ns) {
 		int clk_div;
 
 		/* changing the clk divisor, need to disable fisrt */

drivers/pwm/pwm-lpc18xx-sct.c

@@ -249,7 +249,7 @@ static int lpc18xx_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
 			   LPC18XX_PWM_EVSTATEMSK(lpc18xx_data->duty_event),
 			   LPC18XX_PWM_EVSTATEMSK_ALL);
 
-	if (pwm->polarity == PWM_POLARITY_NORMAL) {
+	if (pwm_get_polarity(pwm) == PWM_POLARITY_NORMAL) {
 		set_event = lpc18xx_pwm->period_event;
 		clear_event = lpc18xx_data->duty_event;
 		res_action = LPC18XX_PWM_RES_SET;

drivers/pwm/pwm-omap-dmtimer.c

@@ -192,7 +192,7 @@ static int pwm_omap_dmtimer_config(struct pwm_chip *chip,
 		load_value, load_value,	match_value, match_value);
 
 	omap->pdata->set_pwm(omap->dm_timer,
-			      pwm->polarity == PWM_POLARITY_INVERSED,
+			      pwm_get_polarity(pwm) == PWM_POLARITY_INVERSED,
 			      true,
 			      PWM_OMAP_DMTIMER_TRIGGER_OVERFLOW_AND_COMPARE);
 

drivers/pwm/pwm-rcar.c

@@ -157,7 +157,7 @@ static int rcar_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
 		return div;
 
 	/* Let the core driver set pwm->period if disabled and duty_ns == 0 */
-	if (!test_bit(PWMF_ENABLED, &pwm->flags) && !duty_ns)
+	if (!pwm_is_enabled(pwm) && !duty_ns)
 		return 0;
 
 	rcar_pwm_update(rp, RCAR_PWMCR_SYNC, RCAR_PWMCR_SYNC, RCAR_PWMCR);

drivers/pwm/pwm-sun4i.c

@@ -354,7 +354,8 @@ static int sun4i_pwm_probe(struct platform_device *pdev)
 	val = sun4i_pwm_readl(pwm, PWM_CTRL_REG);
 	for (i = 0; i < pwm->chip.npwm; i++)
 		if (!(val & BIT_CH(PWM_ACT_STATE, i)))
-			pwm->chip.pwms[i].polarity = PWM_POLARITY_INVERSED;
+			pwm_set_polarity(&pwm->chip.pwms[i],
+					 PWM_POLARITY_INVERSED);
 	clk_disable_unprepare(pwm->clk);
 
 	return 0;

drivers/pwm/sysfs.c

@@ -26,6 +26,7 @@
 struct pwm_export {
 	struct device child;
 	struct pwm_device *pwm;
+	struct mutex lock;
 };
 
 static struct pwm_export *child_to_pwm_export(struct device *child)
@@ -45,15 +46,20 @@ static ssize_t period_show(struct device *child,
 			   char *buf)
 {
 	const struct pwm_device *pwm = child_to_pwm_device(child);
+	struct pwm_state state;
 
-	return sprintf(buf, "%u\n", pwm_get_period(pwm));
+	pwm_get_state(pwm, &state);
+
+	return sprintf(buf, "%u\n", state.period);
 }
 
 static ssize_t period_store(struct device *child,
 			    struct device_attribute *attr,
 			    const char *buf, size_t size)
 {
-	struct pwm_device *pwm = child_to_pwm_device(child);
+	struct pwm_export *export = child_to_pwm_export(child);
+	struct pwm_device *pwm = export->pwm;
+	struct pwm_state state;
 	unsigned int val;
 	int ret;
 
@@ -61,7 +67,11 @@ static ssize_t period_store(struct device *child,
 	if (ret)
 		return ret;
 
-	ret = pwm_config(pwm, pwm_get_duty_cycle(pwm), val);
+	mutex_lock(&export->lock);
+	pwm_get_state(pwm, &state);
+	state.period = val;
+	ret = pwm_apply_state(pwm, &state);
+	mutex_unlock(&export->lock);
 
 	return ret ? : size;
 }
@@ -71,15 +81,20 @@ static ssize_t duty_cycle_show(struct device *child,
 			       char *buf)
 {
 	const struct pwm_device *pwm = child_to_pwm_device(child);
+	struct pwm_state state;
 
-	return sprintf(buf, "%u\n", pwm_get_duty_cycle(pwm));
+	pwm_get_state(pwm, &state);
+
+	return sprintf(buf, "%u\n", state.duty_cycle);
 }
 
 static ssize_t duty_cycle_store(struct device *child,
 				struct device_attribute *attr,
 				const char *buf, size_t size)
 {
-	struct pwm_device *pwm = child_to_pwm_device(child);
+	struct pwm_export *export = child_to_pwm_export(child);
+	struct pwm_device *pwm = export->pwm;
+	struct pwm_state state;
 	unsigned int val;
 	int ret;
 
@@ -87,7 +102,11 @@ static ssize_t duty_cycle_store(struct device *child,
 	if (ret)
 		return ret;
 
-	ret = pwm_config(pwm, val, pwm_get_period(pwm));
+	mutex_lock(&export->lock);
+	pwm_get_state(pwm, &state);
+	state.duty_cycle = val;
+	ret = pwm_apply_state(pwm, &state);
+	mutex_unlock(&export->lock);
 
 	return ret ? : size;
 }
@@ -97,33 +116,46 @@ static ssize_t enable_show(struct device *child,
 			   char *buf)
 {
 	const struct pwm_device *pwm = child_to_pwm_device(child);
+	struct pwm_state state;
 
-	return sprintf(buf, "%d\n", pwm_is_enabled(pwm));
+	pwm_get_state(pwm, &state);
+
+	return sprintf(buf, "%d\n", state.enabled);
 }
 
 static ssize_t enable_store(struct device *child,
 			    struct device_attribute *attr,
 			    const char *buf, size_t size)
 {
-	struct pwm_device *pwm = child_to_pwm_device(child);
+	struct pwm_export *export = child_to_pwm_export(child);
+	struct pwm_device *pwm = export->pwm;
+	struct pwm_state state;
 	int val, ret;
 
 	ret = kstrtoint(buf, 0, &val);
 	if (ret)
 		return ret;
 
+	mutex_lock(&export->lock);
+
+	pwm_get_state(pwm, &state);
+
 	switch (val) {
 	case 0:
-		pwm_disable(pwm);
+		state.enabled = false;
 		break;
 	case 1:
-		ret = pwm_enable(pwm);
+		state.enabled = true;
 		break;
 	default:
 		ret = -EINVAL;
-		break;
+		goto unlock;
 	}
 
+	pwm_apply_state(pwm, &state);
+
+unlock:
+	mutex_unlock(&export->lock);
 	return ret ? : size;
 }
 
@@ -133,8 +165,11 @@ static ssize_t polarity_show(struct device *child,
 {
 	const struct pwm_device *pwm = child_to_pwm_device(child);
 	const char *polarity = "unknown";
+	struct pwm_state state;
 
-	switch (pwm_get_polarity(pwm)) {
+	pwm_get_state(pwm, &state);
+
+	switch (state.polarity) {
 	case PWM_POLARITY_NORMAL:
 		polarity = "normal";
 		break;
@@ -151,8 +186,10 @@ static ssize_t polarity_store(struct device *child,
 			      struct device_attribute *attr,
 			      const char *buf, size_t size)
 {
-	struct pwm_device *pwm = child_to_pwm_device(child);
+	struct pwm_export *export = child_to_pwm_export(child);
+	struct pwm_device *pwm = export->pwm;
 	enum pwm_polarity polarity;
+	struct pwm_state state;
 	int ret;
 
 	if (sysfs_streq(buf, "normal"))
@@ -162,7 +199,11 @@ static ssize_t polarity_store(struct device *child,
 	else
 		return -EINVAL;
 
-	ret = pwm_set_polarity(pwm, polarity);
+	mutex_lock(&export->lock);
+	pwm_get_state(pwm, &state);
+	state.polarity = polarity;
+	ret = pwm_apply_state(pwm, &state);
+	mutex_unlock(&export->lock);
 
 	return ret ? : size;
 }
@@ -203,6 +244,7 @@ static int pwm_export_child(struct device *parent, struct pwm_device *pwm)
 	}
 
 	export->pwm = pwm;
+	mutex_init(&export->lock);
 
 	export->child.release = pwm_export_release;
 	export->child.parent = parent;

drivers/video/backlight/lm3630a_bl.c

@@ -162,7 +162,7 @@ static int lm3630a_intr_config(struct lm3630a_chip *pchip)
 
 static void lm3630a_pwm_ctrl(struct lm3630a_chip *pchip, int br, int br_max)
 {
-	unsigned int period = pwm_get_period(pchip->pwmd);
+	unsigned int period = pchip->pdata->pwm_period;
 	unsigned int duty = br * period / br_max;
 
 	pwm_config(pchip->pwmd, duty, period);
@@ -424,8 +424,13 @@ static int lm3630a_probe(struct i2c_client *client,
 			dev_err(&client->dev, "fail : get pwm device\n");
 			return PTR_ERR(pchip->pwmd);
 		}
+
+		/*
+		 * FIXME: pwm_apply_args() should be removed when switching to
+		 * the atomic PWM API.
+		 */
+		pwm_apply_args(pchip->pwmd);
 	}
-	pchip->pwmd->period = pdata->pwm_period;
 
 	/* interrupt enable  : irq 0 is not allowed */
 	pchip->irq = client->irq;

drivers/video/backlight/lp855x_bl.c

@@ -246,6 +246,12 @@ static void lp855x_pwm_ctrl(struct lp855x *lp, int br, int max_br)
 			return;
 
 		lp->pwm = pwm;
+
+		/*
+		 * FIXME: pwm_apply_args() should be removed when switching to
+		 * the atomic PWM API.
+		 */
+		pwm_apply_args(pwm);
 	}
 
 	pwm_config(lp->pwm, duty, period);

drivers/video/backlight/lp8788_bl.c

@@ -145,6 +145,12 @@ static void lp8788_pwm_ctrl(struct lp8788_bl *bl, int br, int max_br)
 		}
 
 		bl->pwm = pwm;
+
+		/*
+		 * FIXME: pwm_apply_args() should be removed when switching to
+		 * the atomic PWM API.
+		 */
+		pwm_apply_args(pwm);
 	}
 
 	pwm_config(bl->pwm, duty, period);

drivers/video/backlight/pwm_bl.c

@@ -201,6 +201,7 @@ static int pwm_backlight_probe(struct platform_device *pdev)
 	struct device_node *node = pdev->dev.of_node;
 	struct pwm_bl_data *pb;
 	int initial_blank = FB_BLANK_UNBLANK;
+	struct pwm_args pargs;
 	int ret;
 
 	if (!data) {
@@ -306,17 +307,22 @@ static int pwm_backlight_probe(struct platform_device *pdev)
 
 	dev_dbg(&pdev->dev, "got pwm for backlight\n");
 
+	/*
+	 * FIXME: pwm_apply_args() should be removed when switching to
+	 * the atomic PWM API.
+	 */
+	pwm_apply_args(pb->pwm);
+
 	/*
 	 * The DT case will set the pwm_period_ns field to 0 and store the
 	 * period, parsed from the DT, in the PWM device. For the non-DT case,
 	 * set the period from platform data if it has not already been set
 	 * via the PWM lookup table.
 	 */
-	pb->period = pwm_get_period(pb->pwm);
+	pwm_get_args(pb->pwm, &pargs);
-	if (!pb->period && (data->pwm_period_ns > 0)) {
+	pb->period = pargs.period;
+	if (!pb->period && (data->pwm_period_ns > 0))
 		pb->period = data->pwm_period_ns;
-		pwm_set_period(pb->pwm, data->pwm_period_ns);
-	}
 
 	pb->lth_brightness = data->lth_brightness * (pb->period / pb->scale);
 

drivers/video/fbdev/ssd1307fb.c

@@ -286,6 +286,7 @@ static int ssd1307fb_init(struct ssd1307fb_par *par)
 {
 	int ret;
 	u32 precharge, dclk, com_invdir, compins;
+	struct pwm_args pargs;
 
 	if (par->device_info->need_pwm) {
 		par->pwm = pwm_get(&par->client->dev, NULL);
@@ -294,7 +295,15 @@ static int ssd1307fb_init(struct ssd1307fb_par *par)
 			return PTR_ERR(par->pwm);
 		}
 
-		par->pwm_period = pwm_get_period(par->pwm);
+		/*
+		 * FIXME: pwm_apply_args() should be removed when switching to
+		 * the atomic PWM API.
+		 */
+		pwm_apply_args(par->pwm);
+
+		pwm_get_args(par->pwm, &pargs);
+
+		par->pwm_period = pargs.period;
 		/* Enable the PWM */
 		pwm_config(par->pwm, par->pwm_period / 2, par->pwm_period);
 		pwm_enable(par->pwm);

include/linux/pwm.h

@@ -5,59 +5,7 @@
 #include <linux/mutex.h>
 #include <linux/of.h>
 
-struct pwm_device;
 struct seq_file;
-
-#if IS_ENABLED(CONFIG_PWM)
-/*
- * pwm_request - request a PWM device
- */
-struct pwm_device *pwm_request(int pwm_id, const char *label);
-
-/*
- * pwm_free - free a PWM device
- */
-void pwm_free(struct pwm_device *pwm);
-
-/*
- * pwm_config - change a PWM device configuration
- */
-int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns);
-
-/*
- * pwm_enable - start a PWM output toggling
- */
-int pwm_enable(struct pwm_device *pwm);
-
-/*
- * pwm_disable - stop a PWM output toggling
- */
-void pwm_disable(struct pwm_device *pwm);
-#else
-static inline struct pwm_device *pwm_request(int pwm_id, const char *label)
-{
-	return ERR_PTR(-ENODEV);
-}
-
-static inline void pwm_free(struct pwm_device *pwm)
-{
-}
-
-static inline int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns)
-{
-	return -EINVAL;
-}
-
-static inline int pwm_enable(struct pwm_device *pwm)
-{
-	return -EINVAL;
-}
-
-static inline void pwm_disable(struct pwm_device *pwm)
-{
-}
-#endif
-
 struct pwm_chip;
 
 /**
@@ -94,8 +42,21 @@ struct pwm_args {
 
 enum {
 	PWMF_REQUESTED = 1 << 0,
-	PWMF_ENABLED = 1 << 1,
+	PWMF_EXPORTED = 1 << 1,
-	PWMF_EXPORTED = 1 << 2,
+};
+
+/*
+ * struct pwm_state - state of a PWM channel
+ * @period: PWM period (in nanoseconds)
+ * @duty_cycle: PWM duty cycle (in nanoseconds)
+ * @polarity: PWM polarity
+ * @enabled: PWM enabled status
+ */
+struct pwm_state {
+	unsigned int period;
+	unsigned int duty_cycle;
+	enum pwm_polarity polarity;
+	bool enabled;
 };
 
 /**
@@ -106,11 +67,8 @@ enum {
  * @pwm: global index of the PWM device
  * @chip: PWM chip providing this PWM device
  * @chip_data: chip-private data associated with the PWM device
- * @lock: used to serialize accesses to the PWM device where necessary
- * @period: period of the PWM signal (in nanoseconds)
- * @duty_cycle: duty cycle of the PWM signal (in nanoseconds)
- * @polarity: polarity of the PWM signal
  * @args: PWM arguments
+ * @state: curent PWM channel state
  */
 struct pwm_device {
 	const char *label;
@@ -119,50 +77,68 @@ struct pwm_device {
 	unsigned int pwm;
 	struct pwm_chip *chip;
 	void *chip_data;
-	struct mutex lock;
-
-	unsigned int period;
-	unsigned int duty_cycle;
-	enum pwm_polarity polarity;
 
 	struct pwm_args args;
+	struct pwm_state state;
 };
 
+/**
+ * pwm_get_state() - retrieve the current PWM state
+ * @pwm: PWM device
+ * @state: state to fill with the current PWM state
+ */
+static inline void pwm_get_state(const struct pwm_device *pwm,
+				 struct pwm_state *state)
+{
+	*state = pwm->state;
+}
+
 static inline bool pwm_is_enabled(const struct pwm_device *pwm)
 {
-	return test_bit(PWMF_ENABLED, &pwm->flags);
+	struct pwm_state state;
+
+	pwm_get_state(pwm, &state);
+
+	return state.enabled;
 }
 
 static inline void pwm_set_period(struct pwm_device *pwm, unsigned int period)
 {
 	if (pwm)
-		pwm->period = period;
+		pwm->state.period = period;
 }
 
 static inline unsigned int pwm_get_period(const struct pwm_device *pwm)
 {
-	return pwm ? pwm->period : 0;
+	struct pwm_state state;
+
+	pwm_get_state(pwm, &state);
+
+	return state.period;
 }
 
 static inline void pwm_set_duty_cycle(struct pwm_device *pwm, unsigned int duty)
 {
 	if (pwm)
-		pwm->duty_cycle = duty;
+		pwm->state.duty_cycle = duty;
 }
 
 static inline unsigned int pwm_get_duty_cycle(const struct pwm_device *pwm)
 {
-	return pwm ? pwm->duty_cycle : 0;
+	struct pwm_state state;
-}
 
-/*
+	pwm_get_state(pwm, &state);
- * pwm_set_polarity - configure the polarity of a PWM signal
+
- */
+	return state.duty_cycle;
-int pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity);
+}
 
 static inline enum pwm_polarity pwm_get_polarity(const struct pwm_device *pwm)
 {
-	return pwm ? pwm->polarity : PWM_POLARITY_NORMAL;
+	struct pwm_state state;
+
+	pwm_get_state(pwm, &state);
+
+	return state.polarity;
 }
 
 static inline void pwm_get_args(const struct pwm_device *pwm,
@@ -171,12 +147,6 @@ static inline void pwm_get_args(const struct pwm_device *pwm,
 	*args = pwm->args;
 }
 
-static inline void pwm_apply_args(struct pwm_device *pwm)
-{
-	pwm_set_period(pwm, pwm->args.period);
-	pwm_set_polarity(pwm, pwm->args.polarity);
-}
-
 /**
  * struct pwm_ops - PWM controller operations
  * @request: optional hook for requesting a PWM
@@ -185,6 +155,13 @@ static inline void pwm_apply_args(struct pwm_device *pwm)
  * @set_polarity: configure the polarity of this PWM
  * @enable: enable PWM output toggling
  * @disable: disable PWM output toggling
+ * @apply: atomically apply a new PWM config. The state argument
+ *	   should be adjusted with the real hardware config (if the
+ *	   approximate the period or duty_cycle value, state should
+ *	   reflect it)
+ * @get_state: get the current PWM state. This function is only
+ *	       called once per PWM device when the PWM chip is
+ *	       registered.
  * @dbg_show: optional routine to show contents in debugfs
  * @owner: helps prevent removal of modules exporting active PWMs
  */
@@ -197,6 +174,10 @@ struct pwm_ops {
 			    enum pwm_polarity polarity);
 	int (*enable)(struct pwm_chip *chip, struct pwm_device *pwm);
 	void (*disable)(struct pwm_chip *chip, struct pwm_device *pwm);
+	int (*apply)(struct pwm_chip *chip, struct pwm_device *pwm,
+		     struct pwm_state *state);
+	void (*get_state)(struct pwm_chip *chip, struct pwm_device *pwm,
+			  struct pwm_state *state);
 #ifdef CONFIG_DEBUG_FS
 	void (*dbg_show)(struct pwm_chip *chip, struct seq_file *s);
 #endif
@@ -232,6 +213,115 @@ struct pwm_chip {
 };
 
 #if IS_ENABLED(CONFIG_PWM)
+/* PWM user APIs */
+struct pwm_device *pwm_request(int pwm_id, const char *label);
+void pwm_free(struct pwm_device *pwm);
+int pwm_apply_state(struct pwm_device *pwm, struct pwm_state *state);
+int pwm_adjust_config(struct pwm_device *pwm);
+
+/**
+ * pwm_config() - change a PWM device configuration
+ * @pwm: PWM device
+ * @duty_ns: "on" time (in nanoseconds)
+ * @period_ns: duration (in nanoseconds) of one cycle
+ *
+ * Returns: 0 on success or a negative error code on failure.
+ */
+static inline int pwm_config(struct pwm_device *pwm, int duty_ns,
+			     int period_ns)
+{
+	struct pwm_state state;
+
+	if (!pwm)
+		return -EINVAL;
+
+	pwm_get_state(pwm, &state);
+	if (state.duty_cycle == duty_ns && state.period == period_ns)
+		return 0;
+
+	state.duty_cycle = duty_ns;
+	state.period = period_ns;
+	return pwm_apply_state(pwm, &state);
+}
+
+/**
+ * pwm_set_polarity() - configure the polarity of a PWM signal
+ * @pwm: PWM device
+ * @polarity: new polarity of the PWM signal
+ *
+ * Note that the polarity cannot be configured while the PWM device is
+ * enabled.
+ *
+ * Returns: 0 on success or a negative error code on failure.
+ */
+static inline int pwm_set_polarity(struct pwm_device *pwm,
+				   enum pwm_polarity polarity)
+{
+	struct pwm_state state;
+
+	if (!pwm)
+		return -EINVAL;
+
+	pwm_get_state(pwm, &state);
+	if (state.polarity == polarity)
+		return 0;
+
+	/*
+	 * Changing the polarity of a running PWM without adjusting the
+	 * dutycycle/period value is a bit risky (can introduce glitches).
+	 * Return -EBUSY in this case.
+	 * Note that this is allowed when using pwm_apply_state() because
+	 * the user specifies all the parameters.
+	 */
+	if (state.enabled)
+		return -EBUSY;
+
+	state.polarity = polarity;
+	return pwm_apply_state(pwm, &state);
+}
+
+/**
+ * pwm_enable() - start a PWM output toggling
+ * @pwm: PWM device
+ *
+ * Returns: 0 on success or a negative error code on failure.
+ */
+static inline int pwm_enable(struct pwm_device *pwm)
+{
+	struct pwm_state state;
+
+	if (!pwm)
+		return -EINVAL;
+
+	pwm_get_state(pwm, &state);
+	if (state.enabled)
+		return 0;
+
+	state.enabled = true;
+	return pwm_apply_state(pwm, &state);
+}
+
+/**
+ * pwm_disable() - stop a PWM output toggling
+ * @pwm: PWM device
+ */
+static inline void pwm_disable(struct pwm_device *pwm)
+{
+	struct pwm_state state;
+
+	if (!pwm)
+		return;
+
+	pwm_get_state(pwm, &state);
+	if (!state.enabled)
+		return;
+
+	state.enabled = false;
+	pwm_apply_state(pwm, &state);
+}
+
+
+/* PWM provider APIs */
 int pwm_set_chip_data(struct pwm_device *pwm, void *data);
 void *pwm_get_chip_data(struct pwm_device *pwm);
 
@@ -257,6 +347,47 @@ void devm_pwm_put(struct device *dev, struct pwm_device *pwm);
 
 bool pwm_can_sleep(struct pwm_device *pwm);
 #else
+static inline struct pwm_device *pwm_request(int pwm_id, const char *label)
+{
+	return ERR_PTR(-ENODEV);
+}
+
+static inline void pwm_free(struct pwm_device *pwm)
+{
+}
+
+static inline int pwm_apply_state(struct pwm_device *pwm,
+				  const struct pwm_state *state)
+{
+	return -ENOTSUPP;
+}
+
+static inline int pwm_adjust_config(struct pwm_device *pwm)
+{
+	return -ENOTSUPP;
+}
+
+static inline int pwm_config(struct pwm_device *pwm, int duty_ns,
+			     int period_ns)
+{
+	return -EINVAL;
+}
+
+static inline int pwm_set_polarity(struct pwm_device *pwm,
+				   enum pwm_polarity polarity)
+{
+	return -ENOTSUPP;
+}
+
+static inline int pwm_enable(struct pwm_device *pwm)
+{
+	return -EINVAL;
+}
+
+static inline void pwm_disable(struct pwm_device *pwm)
+{
+}
+
 static inline int pwm_set_chip_data(struct pwm_device *pwm, void *data)
 {
 	return -EINVAL;
@@ -328,6 +459,34 @@ static inline bool pwm_can_sleep(struct pwm_device *pwm)
 }
 #endif
 
+static inline void pwm_apply_args(struct pwm_device *pwm)
+{
+	/*
+	 * PWM users calling pwm_apply_args() expect to have a fresh config
+	 * where the polarity and period are set according to pwm_args info.
+	 * The problem is, polarity can only be changed when the PWM is
+	 * disabled.
+	 *
+	 * PWM drivers supporting hardware readout may declare the PWM device
+	 * as enabled, and prevent polarity setting, which changes from the
+	 * existing behavior, where all PWM devices are declared as disabled
+	 * at startup (even if they are actually enabled), thus authorizing
+	 * polarity setting.
+	 *
+	 * Instead of setting ->enabled to false, we call pwm_disable()
+	 * before pwm_set_polarity() to ensure that everything is configured
+	 * as expected, and the PWM is really disabled when the user request
+	 * it.
+	 *
+	 * Note that PWM users requiring a smooth handover between the
+	 * bootloader and the kernel (like critical regulators controlled by
+	 * PWM devices) will have to switch to the atomic API and avoid calling
+	 * pwm_apply_args().
+	 */
+	pwm_disable(pwm);
+	pwm_set_polarity(pwm, pwm->args.polarity);
+}
+
 struct pwm_lookup {
 	struct list_head list;
 	const char *provider;