drivers/pwm/pwm-sl28cpld.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * sl28cpld PWM driver
  *
  * Copyright (c) 2020 Michael Walle <michael@walle.cc>
  *
  * There is no public datasheet available for this PWM core. But it is easy
  * enough to be briefly explained. It consists of one 8-bit counter. The PWM
  * supports four distinct frequencies by selecting when to reset the counter.
  * With the prescaler setting you can select which bit of the counter is used
  * to reset it. This implies that the higher the frequency the less remaining
  * bits are available for the actual counter.
  *
  * Let cnt[7:0] be the counter, clocked at 32kHz:
  * +-----------+--------+--------------+-----------+---------------+
  * | prescaler |  reset | counter bits | frequency | period length |
  * +-----------+--------+--------------+-----------+---------------+
  * |         0 | cnt[7] |     cnt[6:0] |    250 Hz |    4000000 ns |
  * |         1 | cnt[6] |     cnt[5:0] |    500 Hz |    2000000 ns |
  * |         2 | cnt[5] |     cnt[4:0] |     1 kHz |    1000000 ns |
  * |         3 | cnt[4] |     cnt[3:0] |     2 kHz |     500000 ns |
  * +-----------+--------+--------------+-----------+---------------+
  *
  * Limitations:
  * - The hardware cannot generate a 100% duty cycle if the prescaler is 0.
  * - The hardware cannot atomically set the prescaler and the counter value,
  *   which might lead to glitches and inconsistent states if a write fails.
  * - The counter is not reset if you switch the prescaler which leads
  *   to glitches, too.
  * - The duty cycle will switch immediately and not after a complete cycle.
  * - Depending on the actual implementation, disabling the PWM might have
  *   side effects. For example, if the output pin is shared with a GPIO pin
  *   it will automatically switch back to GPIO mode.
  */

 #include <linux/bitfield.h>
 #include <linux/kernel.h>
 #include <linux/mod_devicetable.h>
 #include <linux/module.h>
 #include <linux/platform_device.h>
 #include <linux/property.h>
 #include <linux/pwm.h>
 #include <linux/regmap.h>

 /*
  * PWM timer block registers.
  */
 #define SL28CPLD_PWM_CTRL			0x00
 #define   SL28CPLD_PWM_CTRL_ENABLE		BIT(7)
 #define   SL28CPLD_PWM_CTRL_PRESCALER_MASK	GENMASK(1, 0)
 #define SL28CPLD_PWM_CYCLE			0x01
 #define   SL28CPLD_PWM_CYCLE_MAX		GENMASK(6, 0)

 #define SL28CPLD_PWM_CLK			32000 /* 32 kHz */
 #define SL28CPLD_PWM_MAX_DUTY_CYCLE(prescaler)	(1 << (7 - (prescaler)))
 #define SL28CPLD_PWM_PERIOD(prescaler) \
 	(NSEC_PER_SEC / SL28CPLD_PWM_CLK * SL28CPLD_PWM_MAX_DUTY_CYCLE(prescaler))

 /*
  * We calculate the duty cycle like this:
  *   duty_cycle_ns = pwm_cycle_reg * max_period_ns / max_duty_cycle
  *
  * With
  *   max_period_ns = 1 << (7 - prescaler) / SL28CPLD_PWM_CLK * NSEC_PER_SEC
  *   max_duty_cycle = 1 << (7 - prescaler)
  * this then simplifies to:
  *   duty_cycle_ns = pwm_cycle_reg / SL28CPLD_PWM_CLK * NSEC_PER_SEC
  *                 = NSEC_PER_SEC / SL28CPLD_PWM_CLK * pwm_cycle_reg
  *
  * NSEC_PER_SEC is a multiple of SL28CPLD_PWM_CLK, therefore we're not losing
  * precision by doing the divison first.
  */
 #define SL28CPLD_PWM_TO_DUTY_CYCLE(reg) \
 	(NSEC_PER_SEC / SL28CPLD_PWM_CLK * (reg))
 #define SL28CPLD_PWM_FROM_DUTY_CYCLE(duty_cycle) \
 	(DIV_ROUND_DOWN_ULL((duty_cycle), NSEC_PER_SEC / SL28CPLD_PWM_CLK))

 #define sl28cpld_pwm_read(priv, reg, val) \
 	regmap_read((priv)->regmap, (priv)->offset + (reg), (val))
 #define sl28cpld_pwm_write(priv, reg, val) \
 	regmap_write((priv)->regmap, (priv)->offset + (reg), (val))

 struct sl28cpld_pwm {
 	struct regmap *regmap;
 	u32 offset;
 };

 static inline struct sl28cpld_pwm *sl28cpld_pwm_from_chip(struct pwm_chip *chip)
 {
 	return pwmchip_get_drvdata(chip);
 }

 static int sl28cpld_pwm_get_state(struct pwm_chip *chip,
 				  struct pwm_device *pwm,
 				  struct pwm_state *state)
 {
 	struct sl28cpld_pwm *priv = sl28cpld_pwm_from_chip(chip);
 	unsigned int reg;
 	int prescaler;

 	sl28cpld_pwm_read(priv, SL28CPLD_PWM_CTRL, &reg);

 	state->enabled = reg & SL28CPLD_PWM_CTRL_ENABLE;

 	prescaler = FIELD_GET(SL28CPLD_PWM_CTRL_PRESCALER_MASK, reg);
 	state->period = SL28CPLD_PWM_PERIOD(prescaler);

 	sl28cpld_pwm_read(priv, SL28CPLD_PWM_CYCLE, &reg);
 	state->duty_cycle = SL28CPLD_PWM_TO_DUTY_CYCLE(reg);
 	state->polarity = PWM_POLARITY_NORMAL;

 	/*
 	 * Sanitize values for the PWM core. Depending on the prescaler it
 	 * might happen that we calculate a duty_cycle greater than the actual
 	 * period. This might happen if someone (e.g. the bootloader) sets an
 	 * invalid combination of values. The behavior of the hardware is
 	 * undefined in this case. But we need to report sane values back to
 	 * the PWM core.
 	 */
 	state->duty_cycle = min(state->duty_cycle, state->period);

 	return 0;
 }

 static int sl28cpld_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 			      const struct pwm_state *state)
 {
 	struct sl28cpld_pwm *priv = sl28cpld_pwm_from_chip(chip);
 	unsigned int cycle, prescaler;
 	bool write_duty_cycle_first;
 	int ret;
 	u8 ctrl;

 	/* Polarity inversion is not supported */
 	if (state->polarity != PWM_POLARITY_NORMAL)
 		return -EINVAL;

 	/*
 	 * Calculate the prescaler. Pick the biggest period that isn't
 	 * bigger than the requested period.
 	 */
 	prescaler = DIV_ROUND_UP_ULL(SL28CPLD_PWM_PERIOD(0), state->period);
 	prescaler = order_base_2(prescaler);

 	if (prescaler > field_max(SL28CPLD_PWM_CTRL_PRESCALER_MASK))
 		return -ERANGE;

 	ctrl = FIELD_PREP(SL28CPLD_PWM_CTRL_PRESCALER_MASK, prescaler);
 	if (state->enabled)
 		ctrl |= SL28CPLD_PWM_CTRL_ENABLE;

 	cycle = SL28CPLD_PWM_FROM_DUTY_CYCLE(state->duty_cycle);
 	cycle = min_t(unsigned int, cycle, SL28CPLD_PWM_MAX_DUTY_CYCLE(prescaler));

 	/*
 	 * Work around the hardware limitation. See also above. Trap 100% duty
 	 * cycle if the prescaler is 0. Set prescaler to 1 instead. We don't
 	 * care about the frequency because its "all-one" in either case.
 	 *
 	 * We don't need to check the actual prescaler setting, because only
 	 * if the prescaler is 0 we can have this particular value.
 	 */
 	if (cycle == SL28CPLD_PWM_MAX_DUTY_CYCLE(0)) {
 		ctrl &= ~SL28CPLD_PWM_CTRL_PRESCALER_MASK;
 		ctrl |= FIELD_PREP(SL28CPLD_PWM_CTRL_PRESCALER_MASK, 1);
 		cycle = SL28CPLD_PWM_MAX_DUTY_CYCLE(1);
 	}

 	/*
 	 * To avoid glitches when we switch the prescaler, we have to make sure
 	 * we have a valid duty cycle for the new mode.
 	 *
 	 * Take the current prescaler (or the current period length) into
 	 * account to decide whether we have to write the duty cycle or the new
 	 * prescaler first. If the period length is decreasing we have to
 	 * write the duty cycle first.
 	 */
 	write_duty_cycle_first = pwm->state.period > state->period;

 	if (write_duty_cycle_first) {
 		ret = sl28cpld_pwm_write(priv, SL28CPLD_PWM_CYCLE, cycle);
 		if (ret)
 			return ret;
 	}

 	ret = sl28cpld_pwm_write(priv, SL28CPLD_PWM_CTRL, ctrl);
 	if (ret)
 		return ret;

 	if (!write_duty_cycle_first) {
 		ret = sl28cpld_pwm_write(priv, SL28CPLD_PWM_CYCLE, cycle);
 		if (ret)
 			return ret;
 	}

 	return 0;
 }

 static const struct pwm_ops sl28cpld_pwm_ops = {
 	.apply = sl28cpld_pwm_apply,
 	.get_state = sl28cpld_pwm_get_state,
 };

 static int sl28cpld_pwm_probe(struct platform_device *pdev)
 {
 	struct sl28cpld_pwm *priv;
 	struct pwm_chip *chip;
 	int ret;

 	if (!pdev->dev.parent) {
 		dev_err(&pdev->dev, "no parent device\n");
 		return -ENODEV;
 	}

 	chip = devm_pwmchip_alloc(&pdev->dev, 1, sizeof(*priv));
 	if (IS_ERR(chip))
 		return PTR_ERR(chip);
 	priv = sl28cpld_pwm_from_chip(chip);

 	priv->regmap = dev_get_regmap(pdev->dev.parent, NULL);
 	if (!priv->regmap) {
 		dev_err(&pdev->dev, "could not get parent regmap\n");
 		return -ENODEV;
 	}

 	ret = device_property_read_u32(&pdev->dev, "reg", &priv->offset);
 	if (ret) {
 		dev_err(&pdev->dev, "no 'reg' property found (%pe)\n",
 			ERR_PTR(ret));
 		return -EINVAL;
 	}

 	/* Initialize the pwm_chip structure */
 	chip->ops = &sl28cpld_pwm_ops;

 	ret = devm_pwmchip_add(&pdev->dev, chip);
 	if (ret) {
 		dev_err(&pdev->dev, "failed to add PWM chip (%pe)",
 			ERR_PTR(ret));
 		return ret;
 	}

 	return 0;
 }

 static const struct of_device_id sl28cpld_pwm_of_match[] = {
 	{ .compatible = "kontron,sl28cpld-pwm" },
 	{}
 };
 MODULE_DEVICE_TABLE(of, sl28cpld_pwm_of_match);

 static struct platform_driver sl28cpld_pwm_driver = {
 	.probe = sl28cpld_pwm_probe,
 	.driver = {
 		.name = "sl28cpld-pwm",
 		.of_match_table = sl28cpld_pwm_of_match,
 	},
 };
 module_platform_driver(sl28cpld_pwm_driver);

 MODULE_DESCRIPTION("sl28cpld PWM Driver");
 MODULE_AUTHOR("Michael Walle <michael@walle.cc>");
 MODULE_LICENSE("GPL");
	// SPDX-License-Identifier: GPL-2.0-only
	/*
	* sl28cpld PWM driver
	*
	* Copyright (c) 2020 Michael Walle <michael@walle.cc>
	*
	* There is no public datasheet available for this PWM core. But it is easy
	* enough to be briefly explained. It consists of one 8-bit counter. The PWM
	* supports four distinct frequencies by selecting when to reset the counter.
	* With the prescaler setting you can select which bit of the counter is used
	* to reset it. This implies that the higher the frequency the less remaining
	* bits are available for the actual counter.
	*
	* Let cnt[7:0] be the counter, clocked at 32kHz:
	* +-----------+--------+--------------+-----------+---------------+
	* \| prescaler \| reset \| counter bits \| frequency \| period length \|
	* +-----------+--------+--------------+-----------+---------------+
	* \| 0 \| cnt[7] \| cnt[6:0] \| 250 Hz \| 4000000 ns \|
	* \| 1 \| cnt[6] \| cnt[5:0] \| 500 Hz \| 2000000 ns \|
	* \| 2 \| cnt[5] \| cnt[4:0] \| 1 kHz \| 1000000 ns \|
	* \| 3 \| cnt[4] \| cnt[3:0] \| 2 kHz \| 500000 ns \|
	* +-----------+--------+--------------+-----------+---------------+
	*
	* Limitations:
	* - The hardware cannot generate a 100% duty cycle if the prescaler is 0.
	* - The hardware cannot atomically set the prescaler and the counter value,
	* which might lead to glitches and inconsistent states if a write fails.
	* - The counter is not reset if you switch the prescaler which leads
	* to glitches, too.
	* - The duty cycle will switch immediately and not after a complete cycle.
	* - Depending on the actual implementation, disabling the PWM might have
	* side effects. For example, if the output pin is shared with a GPIO pin
	* it will automatically switch back to GPIO mode.
	*/

	#include <linux/bitfield.h>
	#include <linux/kernel.h>
	#include <linux/mod_devicetable.h>
	#include <linux/module.h>
	#include <linux/platform_device.h>
	#include <linux/property.h>
	#include <linux/pwm.h>
	#include <linux/regmap.h>

	/*
	* PWM timer block registers.
	*/
	#define SL28CPLD_PWM_CTRL 0x00
	#define SL28CPLD_PWM_CTRL_ENABLE BIT(7)
	#define SL28CPLD_PWM_CTRL_PRESCALER_MASK GENMASK(1, 0)
	#define SL28CPLD_PWM_CYCLE 0x01
	#define SL28CPLD_PWM_CYCLE_MAX GENMASK(6, 0)

	#define SL28CPLD_PWM_CLK 32000 /* 32 kHz */
	#define SL28CPLD_PWM_MAX_DUTY_CYCLE(prescaler) (1 << (7 - (prescaler)))
	#define SL28CPLD_PWM_PERIOD(prescaler) \
	(NSEC_PER_SEC / SL28CPLD_PWM_CLK * SL28CPLD_PWM_MAX_DUTY_CYCLE(prescaler))

	/*
	* We calculate the duty cycle like this:
	* duty_cycle_ns = pwm_cycle_reg * max_period_ns / max_duty_cycle
	*
	* With
	* max_period_ns = 1 << (7 - prescaler) / SL28CPLD_PWM_CLK * NSEC_PER_SEC
	* max_duty_cycle = 1 << (7 - prescaler)
	* this then simplifies to:
	* duty_cycle_ns = pwm_cycle_reg / SL28CPLD_PWM_CLK * NSEC_PER_SEC
	* = NSEC_PER_SEC / SL28CPLD_PWM_CLK * pwm_cycle_reg
	*
	* NSEC_PER_SEC is a multiple of SL28CPLD_PWM_CLK, therefore we're not losing
	* precision by doing the divison first.
	*/
	#define SL28CPLD_PWM_TO_DUTY_CYCLE(reg) \
	(NSEC_PER_SEC / SL28CPLD_PWM_CLK * (reg))
	#define SL28CPLD_PWM_FROM_DUTY_CYCLE(duty_cycle) \
	(DIV_ROUND_DOWN_ULL((duty_cycle), NSEC_PER_SEC / SL28CPLD_PWM_CLK))

	#define sl28cpld_pwm_read(priv, reg, val) \
	regmap_read((priv)->regmap, (priv)->offset + (reg), (val))
	#define sl28cpld_pwm_write(priv, reg, val) \
	regmap_write((priv)->regmap, (priv)->offset + (reg), (val))

	struct sl28cpld_pwm {
	struct regmap *regmap;
	u32 offset;
	};

	static inline struct sl28cpld_pwm sl28cpld_pwm_from_chip(struct pwm_chip chip)
	{
	return pwmchip_get_drvdata(chip);
	}

	static int sl28cpld_pwm_get_state(struct pwm_chip *chip,
	struct pwm_device *pwm,
	struct pwm_state *state)
	{
	struct sl28cpld_pwm *priv = sl28cpld_pwm_from_chip(chip);
	unsigned int reg;
	int prescaler;

	sl28cpld_pwm_read(priv, SL28CPLD_PWM_CTRL, &reg);

	state->enabled = reg & SL28CPLD_PWM_CTRL_ENABLE;

	prescaler = FIELD_GET(SL28CPLD_PWM_CTRL_PRESCALER_MASK, reg);
	state->period = SL28CPLD_PWM_PERIOD(prescaler);

	sl28cpld_pwm_read(priv, SL28CPLD_PWM_CYCLE, &reg);
	state->duty_cycle = SL28CPLD_PWM_TO_DUTY_CYCLE(reg);
	state->polarity = PWM_POLARITY_NORMAL;

	/*
	* Sanitize values for the PWM core. Depending on the prescaler it
	* might happen that we calculate a duty_cycle greater than the actual
	* period. This might happen if someone (e.g. the bootloader) sets an
	* invalid combination of values. The behavior of the hardware is
	* undefined in this case. But we need to report sane values back to
	* the PWM core.
	*/
	state->duty_cycle = min(state->duty_cycle, state->period);

	return 0;
	}

	static int sl28cpld_pwm_apply(struct pwm_chip chip, struct pwm_device pwm,
	const struct pwm_state *state)
	{
	struct sl28cpld_pwm *priv = sl28cpld_pwm_from_chip(chip);
	unsigned int cycle, prescaler;
	bool write_duty_cycle_first;
	int ret;
	u8 ctrl;

	/* Polarity inversion is not supported */
	if (state->polarity != PWM_POLARITY_NORMAL)
	return -EINVAL;

	/*
	* Calculate the prescaler. Pick the biggest period that isn't
	* bigger than the requested period.
	*/
	prescaler = DIV_ROUND_UP_ULL(SL28CPLD_PWM_PERIOD(0), state->period);
	prescaler = order_base_2(prescaler);

	if (prescaler > field_max(SL28CPLD_PWM_CTRL_PRESCALER_MASK))
	return -ERANGE;

	ctrl = FIELD_PREP(SL28CPLD_PWM_CTRL_PRESCALER_MASK, prescaler);
	if (state->enabled)
	ctrl \|= SL28CPLD_PWM_CTRL_ENABLE;

	cycle = SL28CPLD_PWM_FROM_DUTY_CYCLE(state->duty_cycle);
	cycle = min_t(unsigned int, cycle, SL28CPLD_PWM_MAX_DUTY_CYCLE(prescaler));

	/*
	* Work around the hardware limitation. See also above. Trap 100% duty
	* cycle if the prescaler is 0. Set prescaler to 1 instead. We don't
	* care about the frequency because its "all-one" in either case.
	*
	* We don't need to check the actual prescaler setting, because only
	* if the prescaler is 0 we can have this particular value.
	*/
	if (cycle == SL28CPLD_PWM_MAX_DUTY_CYCLE(0)) {
	ctrl &= ~SL28CPLD_PWM_CTRL_PRESCALER_MASK;
	ctrl \|= FIELD_PREP(SL28CPLD_PWM_CTRL_PRESCALER_MASK, 1);
	cycle = SL28CPLD_PWM_MAX_DUTY_CYCLE(1);
	}

	/*
	* To avoid glitches when we switch the prescaler, we have to make sure
	* we have a valid duty cycle for the new mode.
	*
	* Take the current prescaler (or the current period length) into
	* account to decide whether we have to write the duty cycle or the new
	* prescaler first. If the period length is decreasing we have to
	* write the duty cycle first.
	*/
	write_duty_cycle_first = pwm->state.period > state->period;

	if (write_duty_cycle_first) {
	ret = sl28cpld_pwm_write(priv, SL28CPLD_PWM_CYCLE, cycle);
	if (ret)
	return ret;
	}

	ret = sl28cpld_pwm_write(priv, SL28CPLD_PWM_CTRL, ctrl);
	if (ret)
	return ret;

	if (!write_duty_cycle_first) {
	ret = sl28cpld_pwm_write(priv, SL28CPLD_PWM_CYCLE, cycle);
	if (ret)
	return ret;
	}

	return 0;
	}

	static const struct pwm_ops sl28cpld_pwm_ops = {
	.apply = sl28cpld_pwm_apply,
	.get_state = sl28cpld_pwm_get_state,
	};

	static int sl28cpld_pwm_probe(struct platform_device *pdev)
	{
	struct sl28cpld_pwm *priv;
	struct pwm_chip *chip;
	int ret;

	if (!pdev->dev.parent) {
	dev_err(&pdev->dev, "no parent device\n");
	return -ENODEV;
	}

	chip = devm_pwmchip_alloc(&pdev->dev, 1, sizeof(*priv));
	if (IS_ERR(chip))
	return PTR_ERR(chip);
	priv = sl28cpld_pwm_from_chip(chip);

	priv->regmap = dev_get_regmap(pdev->dev.parent, NULL);
	if (!priv->regmap) {
	dev_err(&pdev->dev, "could not get parent regmap\n");
	return -ENODEV;
	}

	ret = device_property_read_u32(&pdev->dev, "reg", &priv->offset);
	if (ret) {
	dev_err(&pdev->dev, "no 'reg' property found (%pe)\n",
	ERR_PTR(ret));
	return -EINVAL;
	}

	/* Initialize the pwm_chip structure */
	chip->ops = &sl28cpld_pwm_ops;

	ret = devm_pwmchip_add(&pdev->dev, chip);
	if (ret) {
	dev_err(&pdev->dev, "failed to add PWM chip (%pe)",
	ERR_PTR(ret));
	return ret;
	}

	return 0;
	}

	static const struct of_device_id sl28cpld_pwm_of_match[] = {
	{ .compatible = "kontron,sl28cpld-pwm" },
	{}
	};
	MODULE_DEVICE_TABLE(of, sl28cpld_pwm_of_match);

	static struct platform_driver sl28cpld_pwm_driver = {
	.probe = sl28cpld_pwm_probe,
	.driver = {
	.name = "sl28cpld-pwm",
	.of_match_table = sl28cpld_pwm_of_match,
	},
	};
	module_platform_driver(sl28cpld_pwm_driver);

	MODULE_DESCRIPTION("sl28cpld PWM Driver");
	MODULE_AUTHOR("Michael Walle <michael@walle.cc>");
	MODULE_LICENSE("GPL");