drivers/pwm/pwm-microchip-core.c - third_party/kernel - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * corePWM driver for Microchip "soft" FPGA IP cores.
  *
  * Copyright (c) 2021-2023 Microchip Corporation. All rights reserved.
  * Author: Conor Dooley <conor.dooley@microchip.com>
  * Documentation:
  * https://www.microsemi.com/document-portal/doc_download/1245275-corepwm-hb
  *
  * Limitations:
  * - If the IP block is configured without "shadow registers", all register
  *   writes will take effect immediately, causing glitches on the output.
  *   If shadow registers *are* enabled, setting the "SYNC_UPDATE" register
  *   notifies the core that it needs to update the registers defining the
  *   waveform from the contents of the "shadow registers". Otherwise, changes
  *   will take effective immediately, even for those channels.
  *   As setting the period/duty cycle takes 4 register writes, there is a window
  *   in which this races against the start of a new period.
  * - The IP block has no concept of a duty cycle, only rising/falling edges of
  *   the waveform. Unfortunately, if the rising & falling edges registers have
  *   the same value written to them the IP block will do whichever of a rising
  *   or a falling edge is possible. I.E. a 50% waveform at twice the requested
  *   period. Therefore to get a 0% waveform, the output is set the max high/low
  *   time depending on polarity.
  *   If the duty cycle is 0%, and the requested period is less than the
  *   available period resolution, this will manifest as a ~100% waveform (with
  *   some output glitches) rather than 50%.
  * - The PWM period is set for the whole IP block not per channel. The driver
  *   will only change the period if no other PWM output is enabled.
  */

 #include <linux/clk.h>
 #include <linux/delay.h>
 #include <linux/err.h>
 #include <linux/io.h>
 #include <linux/ktime.h>
 #include <linux/math.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
 #include <linux/of.h>
 #include <linux/platform_device.h>
 #include <linux/pwm.h>

 #define MCHPCOREPWM_PRESCALE_MAX	0xff
 #define MCHPCOREPWM_PERIOD_STEPS_MAX	0xfe
 #define MCHPCOREPWM_PERIOD_MAX		0xff00

 #define MCHPCOREPWM_PRESCALE	0x00
 #define MCHPCOREPWM_PERIOD	0x04
 #define MCHPCOREPWM_EN(i)	(0x08 + 0x04 * (i)) /* 0x08, 0x0c */
 #define MCHPCOREPWM_POSEDGE(i)	(0x10 + 0x08 * (i)) /* 0x10, 0x18, ..., 0x88 */
 #define MCHPCOREPWM_NEGEDGE(i)	(0x14 + 0x08 * (i)) /* 0x14, 0x1c, ..., 0x8c */
 #define MCHPCOREPWM_SYNC_UPD	0xe4
 #define MCHPCOREPWM_TIMEOUT_MS	100u

 struct mchp_core_pwm_chip {
 	struct pwm_chip chip;
 	struct clk *clk;
 	void __iomem *base;
 	struct mutex lock; /* protects the shared period */
 	ktime_t update_timestamp;
 	u32 sync_update_mask;
 	u16 channel_enabled;
 };

 static inline struct mchp_core_pwm_chip *to_mchp_core_pwm(struct pwm_chip *chip)
 {
 	return container_of(chip, struct mchp_core_pwm_chip, chip);
 }

 static void mchp_core_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm,
 				 bool enable, u64 period)
 {
 	struct mchp_core_pwm_chip *mchp_core_pwm = to_mchp_core_pwm(chip);
 	u8 channel_enable, reg_offset, shift;

 	/*
 	 * There are two adjacent 8 bit control regs, the lower reg controls
 	 * 0-7 and the upper reg 8-15. Check if the pwm is in the upper reg
 	 * and if so, offset by the bus width.
 	 */
 	reg_offset = MCHPCOREPWM_EN(pwm->hwpwm >> 3);
 	shift = pwm->hwpwm & 7;

 	channel_enable = readb_relaxed(mchp_core_pwm->base + reg_offset);
 	channel_enable &= ~(1 << shift);
 	channel_enable |= (enable << shift);

 	writel_relaxed(channel_enable, mchp_core_pwm->base + reg_offset);
 	mchp_core_pwm->channel_enabled &= ~BIT(pwm->hwpwm);
 	mchp_core_pwm->channel_enabled |= enable << pwm->hwpwm;

 	/*
 	 * The updated values will not appear on the bus until they have been
 	 * applied to the waveform at the beginning of the next period.
 	 * This is a NO-OP if the channel does not have shadow registers.
 	 */
 	if (mchp_core_pwm->sync_update_mask & (1 << pwm->hwpwm))
 		mchp_core_pwm->update_timestamp = ktime_add_ns(ktime_get(), period);
 }

 static void mchp_core_pwm_wait_for_sync_update(struct mchp_core_pwm_chip *mchp_core_pwm,
 					       unsigned int channel)
 {
 	/*
 	 * If a shadow register is used for this PWM channel, and iff there is
 	 * a pending update to the waveform, we must wait for it to be applied
 	 * before attempting to read its state. Reading the registers yields
 	 * the currently implemented settings & the new ones are only readable
 	 * once the current period has ended.
 	 */

 	if (mchp_core_pwm->sync_update_mask & (1 << channel)) {
 		ktime_t current_time = ktime_get();
 		s64 remaining_ns;
 		u32 delay_us;

 		remaining_ns = ktime_to_ns(ktime_sub(mchp_core_pwm->update_timestamp,
 						     current_time));

 		/*
 		 * If the update has gone through, don't bother waiting for
 		 * obvious reasons. Otherwise wait around for an appropriate
 		 * amount of time for the update to go through.
 		 */
 		if (remaining_ns <= 0)
 			return;

 		delay_us = DIV_ROUND_UP_ULL(remaining_ns, NSEC_PER_USEC);
 		fsleep(delay_us);
 	}
 }

 static u64 mchp_core_pwm_calc_duty(const struct pwm_state *state, u64 clk_rate,
 				   u8 prescale, u8 period_steps)
 {
 	u64 duty_steps, tmp;

 	/*
 	 * Calculate the duty cycle in multiples of the prescaled period:
 	 * duty_steps = duty_in_ns / step_in_ns
 	 * step_in_ns = (prescale * NSEC_PER_SEC) / clk_rate
 	 * The code below is rearranged slightly to only divide once.
 	 */
 	tmp = (((u64)prescale) + 1) * NSEC_PER_SEC;
 	duty_steps = mul_u64_u64_div_u64(state->duty_cycle, clk_rate, tmp);

 	return duty_steps;
 }

 static void mchp_core_pwm_apply_duty(struct pwm_chip *chip, struct pwm_device *pwm,
 				     const struct pwm_state *state, u64 duty_steps,
 				     u16 period_steps)
 {
 	struct mchp_core_pwm_chip *mchp_core_pwm = to_mchp_core_pwm(chip);
 	u8 posedge, negedge;
 	u8 first_edge = 0, second_edge = duty_steps;

 	/*
 	 * Setting posedge == negedge doesn't yield a constant output,
 	 * so that's an unsuitable setting to model duty_steps = 0.
 	 * In that case set the unwanted edge to a value that never
 	 * triggers.
 	 */
 	if (duty_steps == 0)
 		first_edge = period_steps + 1;

 	if (state->polarity == PWM_POLARITY_INVERSED) {
 		negedge = first_edge;
 		posedge = second_edge;
 	} else {
 		posedge = first_edge;
 		negedge = second_edge;
 	}

 	/*
 	 * Set the sync bit which ensures that periods that already started are
 	 * completed unaltered. At each counter reset event the values are
 	 * updated from the shadow registers.
 	 */
 	writel_relaxed(posedge, mchp_core_pwm->base + MCHPCOREPWM_POSEDGE(pwm->hwpwm));
 	writel_relaxed(negedge, mchp_core_pwm->base + MCHPCOREPWM_NEGEDGE(pwm->hwpwm));
 }

 static int mchp_core_pwm_calc_period(const struct pwm_state *state, unsigned long clk_rate,
 				     u16 *prescale, u16 *period_steps)
 {
 	u64 tmp;

 	/*
 	 * Calculate the period cycles and prescale values.
 	 * The registers are each 8 bits wide & multiplied to compute the period
 	 * using the formula:
 	 *           (prescale + 1) * (period_steps + 1)
 	 * period = -------------------------------------
 	 *                      clk_rate
 	 * so the maximum period that can be generated is 0x10000 times the
 	 * period of the input clock.
 	 * However, due to the design of the "hardware", it is not possible to
 	 * attain a 100% duty cycle if the full range of period_steps is used.
 	 * Therefore period_steps is restricted to 0xfe and the maximum multiple
 	 * of the clock period attainable is (0xff + 1) * (0xfe + 1) = 0xff00
 	 *
 	 * The prescale and period_steps registers operate similarly to
 	 * CLK_DIVIDER_ONE_BASED, where the value used by the hardware is that
 	 * in the register plus one.
 	 * It's therefore not possible to set a period lower than 1/clk_rate, so
 	 * if tmp is 0, abort. Without aborting, we will set a period that is
 	 * greater than that requested and, more importantly, will trigger the
 	 * neg-/pos-edge issue described in the limitations.
 	 */
 	tmp = mul_u64_u64_div_u64(state->period, clk_rate, NSEC_PER_SEC);
 	if (tmp >= MCHPCOREPWM_PERIOD_MAX) {
 		*prescale = MCHPCOREPWM_PRESCALE_MAX;
 		*period_steps = MCHPCOREPWM_PERIOD_STEPS_MAX;

 		return 0;
 	}

 	/*
 	 * There are multiple strategies that could be used to choose the
 	 * prescale & period_steps values.
 	 * Here the idea is to pick values so that the selection of duty cycles
 	 * is as finegrain as possible, while also keeping the period less than
 	 * that requested.
 	 *
 	 * A simple way to satisfy the first condition is to always set
 	 * period_steps to its maximum value. This neatly also satisfies the
 	 * second condition too, since using the maximum value of period_steps
 	 * to calculate prescale actually calculates its upper bound.
 	 * Integer division will ensure a round down, so the period will thereby
 	 * always be less than that requested.
 	 *
 	 * The downside of this approach is a significant degree of inaccuracy,
 	 * especially as tmp approaches integer multiples of
 	 * MCHPCOREPWM_PERIOD_STEPS_MAX.
 	 *
 	 * As we must produce a period less than that requested, and for the
 	 * sake of creating a simple algorithm, disallow small values of tmp
 	 * that would need special handling.
 	 */
 	if (tmp < MCHPCOREPWM_PERIOD_STEPS_MAX + 1)
 		return -EINVAL;

 	/*
 	 * This "optimal" value for prescale is be calculated using the maximum
 	 * permitted value of period_steps, 0xfe.
 	 *
 	 *                period * clk_rate
 	 * prescale = ------------------------- - 1
 	 *            NSEC_PER_SEC * (0xfe + 1)
 	 *
 	 *
 	 *  period * clk_rate
 	 * ------------------- was precomputed as `tmp`
 	 *    NSEC_PER_SEC
 	 */
 	*prescale = ((u16)tmp) / (MCHPCOREPWM_PERIOD_STEPS_MAX + 1) - 1;

 	/*
 	 * period_steps can be computed from prescale:
 	 *                      period * clk_rate
 	 * period_steps = ----------------------------- - 1
 	 *                NSEC_PER_SEC * (prescale + 1)
 	 *
 	 * However, in this approximation, we simply use the maximum value that
 	 * was used to compute prescale.
 	 */
 	*period_steps = MCHPCOREPWM_PERIOD_STEPS_MAX;

 	return 0;
 }

 static int mchp_core_pwm_apply_locked(struct pwm_chip *chip, struct pwm_device *pwm,
 				      const struct pwm_state *state)
 {
 	struct mchp_core_pwm_chip *mchp_core_pwm = to_mchp_core_pwm(chip);
 	bool period_locked;
 	unsigned long clk_rate;
 	u64 duty_steps;
 	u16 prescale, period_steps;
 	int ret;

 	if (!state->enabled) {
 		mchp_core_pwm_enable(chip, pwm, false, pwm->state.period);
 		return 0;
 	}

 	/*
 	 * If clk_rate is too big, the following multiplication might overflow.
 	 * However this is implausible, as the fabric of current FPGAs cannot
 	 * provide clocks at a rate high enough.
 	 */
 	clk_rate = clk_get_rate(mchp_core_pwm->clk);
 	if (clk_rate >= NSEC_PER_SEC)
 		return -EINVAL;

 	ret = mchp_core_pwm_calc_period(state, clk_rate, &prescale, &period_steps);
 	if (ret)
 		return ret;

 	/*
 	 * If the only thing that has changed is the duty cycle or the polarity,
 	 * we can shortcut the calculations and just compute/apply the new duty
 	 * cycle pos & neg edges
 	 * As all the channels share the same period, do not allow it to be
 	 * changed if any other channels are enabled.
 	 * If the period is locked, it may not be possible to use a period
 	 * less than that requested. In that case, we just abort.
 	 */
 	period_locked = mchp_core_pwm->channel_enabled & ~(1 << pwm->hwpwm);

 	if (period_locked) {
 		u16 hw_prescale;
 		u16 hw_period_steps;

 		hw_prescale = readb_relaxed(mchp_core_pwm->base + MCHPCOREPWM_PRESCALE);
 		hw_period_steps = readb_relaxed(mchp_core_pwm->base + MCHPCOREPWM_PERIOD);

 		if ((period_steps + 1) * (prescale + 1) <
 		    (hw_period_steps + 1) * (hw_prescale + 1))
 			return -EINVAL;

 		/*
 		 * It is possible that something could have set the period_steps
 		 * register to 0xff, which would prevent us from setting a 100%
 		 * or 0% relative duty cycle, as explained above in
 		 * mchp_core_pwm_calc_period().
 		 * The period is locked and we cannot change this, so we abort.
 		 */
 		if (hw_period_steps > MCHPCOREPWM_PERIOD_STEPS_MAX)
 			return -EINVAL;

 		prescale = hw_prescale;
 		period_steps = hw_period_steps;
 	}

 	duty_steps = mchp_core_pwm_calc_duty(state, clk_rate, prescale, period_steps);

 	/*
 	 * Because the period is not per channel, it is possible that the
 	 * requested duty cycle is longer than the period, in which case cap it
 	 * to the period, IOW a 100% duty cycle.
 	 */
 	if (duty_steps > period_steps)
 		duty_steps = period_steps + 1;

 	if (!period_locked) {
 		writel_relaxed(prescale, mchp_core_pwm->base + MCHPCOREPWM_PRESCALE);
 		writel_relaxed(period_steps, mchp_core_pwm->base + MCHPCOREPWM_PERIOD);
 	}

 	mchp_core_pwm_apply_duty(chip, pwm, state, duty_steps, period_steps);

 	mchp_core_pwm_enable(chip, pwm, true, pwm->state.period);

 	return 0;
 }

 static int mchp_core_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 			       const struct pwm_state *state)
 {
 	struct mchp_core_pwm_chip *mchp_core_pwm = to_mchp_core_pwm(chip);
 	int ret;

 	mutex_lock(&mchp_core_pwm->lock);

 	mchp_core_pwm_wait_for_sync_update(mchp_core_pwm, pwm->hwpwm);

 	ret = mchp_core_pwm_apply_locked(chip, pwm, state);

 	mutex_unlock(&mchp_core_pwm->lock);

 	return ret;
 }

 static int mchp_core_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
 				   struct pwm_state *state)
 {
 	struct mchp_core_pwm_chip *mchp_core_pwm = to_mchp_core_pwm(chip);
 	u64 rate;
 	u16 prescale, period_steps;
 	u8 duty_steps, posedge, negedge;

 	mutex_lock(&mchp_core_pwm->lock);

 	mchp_core_pwm_wait_for_sync_update(mchp_core_pwm, pwm->hwpwm);

 	if (mchp_core_pwm->channel_enabled & (1 << pwm->hwpwm))
 		state->enabled = true;
 	else
 		state->enabled = false;

 	rate = clk_get_rate(mchp_core_pwm->clk);

 	/*
 	 * Calculating the period:
 	 * The registers are each 8 bits wide & multiplied to compute the period
 	 * using the formula:
 	 *           (prescale + 1) * (period_steps + 1)
 	 * period = -------------------------------------
 	 *                      clk_rate
 	 *
 	 * Note:
 	 * The prescale and period_steps registers operate similarly to
 	 * CLK_DIVIDER_ONE_BASED, where the value used by the hardware is that
 	 * in the register plus one.
 	 */
 	prescale = readb_relaxed(mchp_core_pwm->base + MCHPCOREPWM_PRESCALE);
 	period_steps = readb_relaxed(mchp_core_pwm->base + MCHPCOREPWM_PERIOD);

 	state->period = (period_steps + 1) * (prescale + 1);
 	state->period *= NSEC_PER_SEC;
 	state->period = DIV64_U64_ROUND_UP(state->period, rate);

 	posedge = readb_relaxed(mchp_core_pwm->base + MCHPCOREPWM_POSEDGE(pwm->hwpwm));
 	negedge = readb_relaxed(mchp_core_pwm->base + MCHPCOREPWM_NEGEDGE(pwm->hwpwm));

 	mutex_unlock(&mchp_core_pwm->lock);

 	if (negedge == posedge) {
 		state->duty_cycle = state->period;
 		state->period *= 2;
 	} else {
 		duty_steps = abs((s16)posedge - (s16)negedge);
 		state->duty_cycle = duty_steps * (prescale + 1) * NSEC_PER_SEC;
 		state->duty_cycle = DIV64_U64_ROUND_UP(state->duty_cycle, rate);
 	}

 	state->polarity = negedge < posedge ? PWM_POLARITY_INVERSED : PWM_POLARITY_NORMAL;

 	return 0;
 }

 static const struct pwm_ops mchp_core_pwm_ops = {
 	.apply = mchp_core_pwm_apply,
 	.get_state = mchp_core_pwm_get_state,
 	.owner = THIS_MODULE,
 };

 static const struct of_device_id mchp_core_of_match[] = {
 	{
 		.compatible = "microchip,corepwm-rtl-v4",
 	},
 	{ /* sentinel */ }
 };
 MODULE_DEVICE_TABLE(of, mchp_core_of_match);

 static int mchp_core_pwm_probe(struct platform_device *pdev)
 {
 	struct mchp_core_pwm_chip *mchp_core_pwm;
 	struct resource *regs;
 	int ret;

 	mchp_core_pwm = devm_kzalloc(&pdev->dev, sizeof(*mchp_core_pwm), GFP_KERNEL);
 	if (!mchp_core_pwm)
 		return -ENOMEM;

 	mchp_core_pwm->base = devm_platform_get_and_ioremap_resource(pdev, 0, &regs);
 	if (IS_ERR(mchp_core_pwm->base))
 		return PTR_ERR(mchp_core_pwm->base);

 	mchp_core_pwm->clk = devm_clk_get_enabled(&pdev->dev, NULL);
 	if (IS_ERR(mchp_core_pwm->clk))
 		return dev_err_probe(&pdev->dev, PTR_ERR(mchp_core_pwm->clk),
 				     "failed to get PWM clock\n");

 	if (of_property_read_u32(pdev->dev.of_node, "microchip,sync-update-mask",
 				 &mchp_core_pwm->sync_update_mask))
 		mchp_core_pwm->sync_update_mask = 0;

 	mutex_init(&mchp_core_pwm->lock);

 	mchp_core_pwm->chip.dev = &pdev->dev;
 	mchp_core_pwm->chip.ops = &mchp_core_pwm_ops;
 	mchp_core_pwm->chip.npwm = 16;

 	mchp_core_pwm->channel_enabled = readb_relaxed(mchp_core_pwm->base + MCHPCOREPWM_EN(0));
 	mchp_core_pwm->channel_enabled |=
 		readb_relaxed(mchp_core_pwm->base + MCHPCOREPWM_EN(1)) << 8;

 	/*
 	 * Enable synchronous update mode for all channels for which shadow
 	 * registers have been synthesised.
 	 */
 	writel_relaxed(1U, mchp_core_pwm->base + MCHPCOREPWM_SYNC_UPD);
 	mchp_core_pwm->update_timestamp = ktime_get();

 	ret = devm_pwmchip_add(&pdev->dev, &mchp_core_pwm->chip);
 	if (ret)
 		return dev_err_probe(&pdev->dev, ret, "Failed to add pwmchip\n");

 	return 0;
 }

 static struct platform_driver mchp_core_pwm_driver = {
 	.driver = {
 		.name = "mchp-core-pwm",
 		.of_match_table = mchp_core_of_match,
 	},
 	.probe = mchp_core_pwm_probe,
 };
 module_platform_driver(mchp_core_pwm_driver);

 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Conor Dooley <conor.dooley@microchip.com>");
 MODULE_DESCRIPTION("corePWM driver for Microchip FPGAs");
	// SPDX-License-Identifier: GPL-2.0
	/*
	* corePWM driver for Microchip "soft" FPGA IP cores.
	*
	* Copyright (c) 2021-2023 Microchip Corporation. All rights reserved.
	* Author: Conor Dooley <conor.dooley@microchip.com>
	* Documentation:
	* https://www.microsemi.com/document-portal/doc_download/1245275-corepwm-hb
	*
	* Limitations:
	* - If the IP block is configured without "shadow registers", all register
	* writes will take effect immediately, causing glitches on the output.
	* If shadow registers are enabled, setting the "SYNC_UPDATE" register
	* notifies the core that it needs to update the registers defining the
	* waveform from the contents of the "shadow registers". Otherwise, changes
	* will take effective immediately, even for those channels.
	* As setting the period/duty cycle takes 4 register writes, there is a window
	* in which this races against the start of a new period.
	* - The IP block has no concept of a duty cycle, only rising/falling edges of
	* the waveform. Unfortunately, if the rising & falling edges registers have
	* the same value written to them the IP block will do whichever of a rising
	* or a falling edge is possible. I.E. a 50% waveform at twice the requested
	* period. Therefore to get a 0% waveform, the output is set the max high/low
	* time depending on polarity.
	* If the duty cycle is 0%, and the requested period is less than the
	* available period resolution, this will manifest as a ~100% waveform (with
	* some output glitches) rather than 50%.
	* - The PWM period is set for the whole IP block not per channel. The driver
	* will only change the period if no other PWM output is enabled.
	*/

	#include <linux/clk.h>
	#include <linux/delay.h>
	#include <linux/err.h>
	#include <linux/io.h>
	#include <linux/ktime.h>
	#include <linux/math.h>
	#include <linux/module.h>
	#include <linux/mutex.h>
	#include <linux/of.h>
	#include <linux/platform_device.h>
	#include <linux/pwm.h>

	#define MCHPCOREPWM_PRESCALE_MAX 0xff
	#define MCHPCOREPWM_PERIOD_STEPS_MAX 0xfe
	#define MCHPCOREPWM_PERIOD_MAX 0xff00

	#define MCHPCOREPWM_PRESCALE 0x00
	#define MCHPCOREPWM_PERIOD 0x04
	#define MCHPCOREPWM_EN(i) (0x08 + 0x04 * (i)) /* 0x08, 0x0c */
	#define MCHPCOREPWM_POSEDGE(i) (0x10 + 0x08 * (i)) /* 0x10, 0x18, ..., 0x88 */
	#define MCHPCOREPWM_NEGEDGE(i) (0x14 + 0x08 * (i)) /* 0x14, 0x1c, ..., 0x8c */
	#define MCHPCOREPWM_SYNC_UPD 0xe4
	#define MCHPCOREPWM_TIMEOUT_MS 100u

	struct mchp_core_pwm_chip {
	struct pwm_chip chip;
	struct clk *clk;
	void __iomem *base;
	struct mutex lock; /* protects the shared period */
	ktime_t update_timestamp;
	u32 sync_update_mask;
	u16 channel_enabled;
	};

	static inline struct mchp_core_pwm_chip to_mchp_core_pwm(struct pwm_chip chip)
	{
	return container_of(chip, struct mchp_core_pwm_chip, chip);
	}

	static void mchp_core_pwm_enable(struct pwm_chip chip, struct pwm_device pwm,
	bool enable, u64 period)
	{
	struct mchp_core_pwm_chip *mchp_core_pwm = to_mchp_core_pwm(chip);
	u8 channel_enable, reg_offset, shift;

	/*
	* There are two adjacent 8 bit control regs, the lower reg controls
	* 0-7 and the upper reg 8-15. Check if the pwm is in the upper reg
	* and if so, offset by the bus width.
	*/
	reg_offset = MCHPCOREPWM_EN(pwm->hwpwm >> 3);
	shift = pwm->hwpwm & 7;

	channel_enable = readb_relaxed(mchp_core_pwm->base + reg_offset);
	channel_enable &= ~(1 << shift);
	channel_enable \|= (enable << shift);

	writel_relaxed(channel_enable, mchp_core_pwm->base + reg_offset);
	mchp_core_pwm->channel_enabled &= ~BIT(pwm->hwpwm);
	mchp_core_pwm->channel_enabled \|= enable << pwm->hwpwm;

	/*
	* The updated values will not appear on the bus until they have been
	* applied to the waveform at the beginning of the next period.
	* This is a NO-OP if the channel does not have shadow registers.
	*/
	if (mchp_core_pwm->sync_update_mask & (1 << pwm->hwpwm))
	mchp_core_pwm->update_timestamp = ktime_add_ns(ktime_get(), period);
	}

	static void mchp_core_pwm_wait_for_sync_update(struct mchp_core_pwm_chip *mchp_core_pwm,
	unsigned int channel)
	{
	/*
	* If a shadow register is used for this PWM channel, and iff there is
	* a pending update to the waveform, we must wait for it to be applied
	* before attempting to read its state. Reading the registers yields
	* the currently implemented settings & the new ones are only readable
	* once the current period has ended.
	*/

	if (mchp_core_pwm->sync_update_mask & (1 << channel)) {
	ktime_t current_time = ktime_get();
	s64 remaining_ns;
	u32 delay_us;

	remaining_ns = ktime_to_ns(ktime_sub(mchp_core_pwm->update_timestamp,
	current_time));

	/*
	* If the update has gone through, don't bother waiting for
	* obvious reasons. Otherwise wait around for an appropriate
	* amount of time for the update to go through.
	*/
	if (remaining_ns <= 0)
	return;

	delay_us = DIV_ROUND_UP_ULL(remaining_ns, NSEC_PER_USEC);
	fsleep(delay_us);
	}
	}

	static u64 mchp_core_pwm_calc_duty(const struct pwm_state *state, u64 clk_rate,
	u8 prescale, u8 period_steps)
	{
	u64 duty_steps, tmp;

	/*
	* Calculate the duty cycle in multiples of the prescaled period:
	* duty_steps = duty_in_ns / step_in_ns
	* step_in_ns = (prescale * NSEC_PER_SEC) / clk_rate
	* The code below is rearranged slightly to only divide once.
	*/
	tmp = (((u64)prescale) + 1) * NSEC_PER_SEC;
	duty_steps = mul_u64_u64_div_u64(state->duty_cycle, clk_rate, tmp);

	return duty_steps;
	}

	static void mchp_core_pwm_apply_duty(struct pwm_chip chip, struct pwm_device pwm,
	const struct pwm_state *state, u64 duty_steps,
	u16 period_steps)
	{
	struct mchp_core_pwm_chip *mchp_core_pwm = to_mchp_core_pwm(chip);
	u8 posedge, negedge;
	u8 first_edge = 0, second_edge = duty_steps;

	/*
	* Setting posedge == negedge doesn't yield a constant output,
	* so that's an unsuitable setting to model duty_steps = 0.
	* In that case set the unwanted edge to a value that never
	* triggers.
	*/
	if (duty_steps == 0)
	first_edge = period_steps + 1;

	if (state->polarity == PWM_POLARITY_INVERSED) {
	negedge = first_edge;
	posedge = second_edge;
	} else {
	posedge = first_edge;
	negedge = second_edge;
	}

	/*
	* Set the sync bit which ensures that periods that already started are
	* completed unaltered. At each counter reset event the values are
	* updated from the shadow registers.
	*/
	writel_relaxed(posedge, mchp_core_pwm->base + MCHPCOREPWM_POSEDGE(pwm->hwpwm));
	writel_relaxed(negedge, mchp_core_pwm->base + MCHPCOREPWM_NEGEDGE(pwm->hwpwm));
	}

	static int mchp_core_pwm_calc_period(const struct pwm_state *state, unsigned long clk_rate,
	u16 prescale, u16 period_steps)
	{
	u64 tmp;

	/*
	* Calculate the period cycles and prescale values.
	* The registers are each 8 bits wide & multiplied to compute the period
	* using the formula:
	* (prescale + 1) * (period_steps + 1)
	* period = -------------------------------------
	* clk_rate
	* so the maximum period that can be generated is 0x10000 times the
	* period of the input clock.
	* However, due to the design of the "hardware", it is not possible to
	* attain a 100% duty cycle if the full range of period_steps is used.
	* Therefore period_steps is restricted to 0xfe and the maximum multiple
	* of the clock period attainable is (0xff + 1) * (0xfe + 1) = 0xff00
	*
	* The prescale and period_steps registers operate similarly to
	* CLK_DIVIDER_ONE_BASED, where the value used by the hardware is that
	* in the register plus one.
	* It's therefore not possible to set a period lower than 1/clk_rate, so
	* if tmp is 0, abort. Without aborting, we will set a period that is
	* greater than that requested and, more importantly, will trigger the
	* neg-/pos-edge issue described in the limitations.
	*/
	tmp = mul_u64_u64_div_u64(state->period, clk_rate, NSEC_PER_SEC);
	if (tmp >= MCHPCOREPWM_PERIOD_MAX) {
	*prescale = MCHPCOREPWM_PRESCALE_MAX;
	*period_steps = MCHPCOREPWM_PERIOD_STEPS_MAX;

	return 0;
	}

	/*
	* There are multiple strategies that could be used to choose the
	* prescale & period_steps values.
	* Here the idea is to pick values so that the selection of duty cycles
	* is as finegrain as possible, while also keeping the period less than
	* that requested.
	*
	* A simple way to satisfy the first condition is to always set
	* period_steps to its maximum value. This neatly also satisfies the
	* second condition too, since using the maximum value of period_steps
	* to calculate prescale actually calculates its upper bound.
	* Integer division will ensure a round down, so the period will thereby
	* always be less than that requested.
	*
	* The downside of this approach is a significant degree of inaccuracy,
	* especially as tmp approaches integer multiples of
	* MCHPCOREPWM_PERIOD_STEPS_MAX.
	*
	* As we must produce a period less than that requested, and for the
	* sake of creating a simple algorithm, disallow small values of tmp
	* that would need special handling.
	*/
	if (tmp < MCHPCOREPWM_PERIOD_STEPS_MAX + 1)
	return -EINVAL;

	/*
	* This "optimal" value for prescale is be calculated using the maximum
	* permitted value of period_steps, 0xfe.
	*
	* period * clk_rate
	* prescale = ------------------------- - 1
	* NSEC_PER_SEC * (0xfe + 1)
	*
	*
	* period * clk_rate
	* ------------------- was precomputed as `tmp`
	* NSEC_PER_SEC
	*/
	*prescale = ((u16)tmp) / (MCHPCOREPWM_PERIOD_STEPS_MAX + 1) - 1;

	/*
	* period_steps can be computed from prescale:
	* period * clk_rate
	* period_steps = ----------------------------- - 1
	* NSEC_PER_SEC * (prescale + 1)
	*
	* However, in this approximation, we simply use the maximum value that
	* was used to compute prescale.
	*/
	*period_steps = MCHPCOREPWM_PERIOD_STEPS_MAX;

	return 0;
	}

	static int mchp_core_pwm_apply_locked(struct pwm_chip chip, struct pwm_device pwm,
	const struct pwm_state *state)
	{
	struct mchp_core_pwm_chip *mchp_core_pwm = to_mchp_core_pwm(chip);
	bool period_locked;
	unsigned long clk_rate;
	u64 duty_steps;
	u16 prescale, period_steps;
	int ret;

	if (!state->enabled) {
	mchp_core_pwm_enable(chip, pwm, false, pwm->state.period);
	return 0;
	}

	/*
	* If clk_rate is too big, the following multiplication might overflow.
	* However this is implausible, as the fabric of current FPGAs cannot
	* provide clocks at a rate high enough.
	*/
	clk_rate = clk_get_rate(mchp_core_pwm->clk);
	if (clk_rate >= NSEC_PER_SEC)
	return -EINVAL;

	ret = mchp_core_pwm_calc_period(state, clk_rate, &prescale, &period_steps);
	if (ret)
	return ret;

	/*
	* If the only thing that has changed is the duty cycle or the polarity,
	* we can shortcut the calculations and just compute/apply the new duty
	* cycle pos & neg edges
	* As all the channels share the same period, do not allow it to be
	* changed if any other channels are enabled.
	* If the period is locked, it may not be possible to use a period
	* less than that requested. In that case, we just abort.
	*/
	period_locked = mchp_core_pwm->channel_enabled & ~(1 << pwm->hwpwm);

	if (period_locked) {
	u16 hw_prescale;
	u16 hw_period_steps;

	hw_prescale = readb_relaxed(mchp_core_pwm->base + MCHPCOREPWM_PRESCALE);
	hw_period_steps = readb_relaxed(mchp_core_pwm->base + MCHPCOREPWM_PERIOD);

	if ((period_steps + 1) * (prescale + 1) <
	(hw_period_steps + 1) * (hw_prescale + 1))
	return -EINVAL;

	/*
	* It is possible that something could have set the period_steps
	* register to 0xff, which would prevent us from setting a 100%
	* or 0% relative duty cycle, as explained above in
	* mchp_core_pwm_calc_period().
	* The period is locked and we cannot change this, so we abort.
	*/
	if (hw_period_steps > MCHPCOREPWM_PERIOD_STEPS_MAX)
	return -EINVAL;

	prescale = hw_prescale;
	period_steps = hw_period_steps;
	}

	duty_steps = mchp_core_pwm_calc_duty(state, clk_rate, prescale, period_steps);

	/*
	* Because the period is not per channel, it is possible that the
	* requested duty cycle is longer than the period, in which case cap it
	* to the period, IOW a 100% duty cycle.
	*/
	if (duty_steps > period_steps)
	duty_steps = period_steps + 1;

	if (!period_locked) {
	writel_relaxed(prescale, mchp_core_pwm->base + MCHPCOREPWM_PRESCALE);
	writel_relaxed(period_steps, mchp_core_pwm->base + MCHPCOREPWM_PERIOD);
	}

	mchp_core_pwm_apply_duty(chip, pwm, state, duty_steps, period_steps);

	mchp_core_pwm_enable(chip, pwm, true, pwm->state.period);

	return 0;
	}

	static int mchp_core_pwm_apply(struct pwm_chip chip, struct pwm_device pwm,
	const struct pwm_state *state)
	{
	struct mchp_core_pwm_chip *mchp_core_pwm = to_mchp_core_pwm(chip);
	int ret;

	mutex_lock(&mchp_core_pwm->lock);

	mchp_core_pwm_wait_for_sync_update(mchp_core_pwm, pwm->hwpwm);

	ret = mchp_core_pwm_apply_locked(chip, pwm, state);

	mutex_unlock(&mchp_core_pwm->lock);

	return ret;
	}

	static int mchp_core_pwm_get_state(struct pwm_chip chip, struct pwm_device pwm,
	struct pwm_state *state)
	{
	struct mchp_core_pwm_chip *mchp_core_pwm = to_mchp_core_pwm(chip);
	u64 rate;
	u16 prescale, period_steps;
	u8 duty_steps, posedge, negedge;

	mutex_lock(&mchp_core_pwm->lock);

	mchp_core_pwm_wait_for_sync_update(mchp_core_pwm, pwm->hwpwm);

	if (mchp_core_pwm->channel_enabled & (1 << pwm->hwpwm))
	state->enabled = true;
	else
	state->enabled = false;

	rate = clk_get_rate(mchp_core_pwm->clk);

	/*
	* Calculating the period:
	* The registers are each 8 bits wide & multiplied to compute the period
	* using the formula:
	* (prescale + 1) * (period_steps + 1)
	* period = -------------------------------------
	* clk_rate
	*
	* Note:
	* The prescale and period_steps registers operate similarly to
	* CLK_DIVIDER_ONE_BASED, where the value used by the hardware is that
	* in the register plus one.
	*/
	prescale = readb_relaxed(mchp_core_pwm->base + MCHPCOREPWM_PRESCALE);
	period_steps = readb_relaxed(mchp_core_pwm->base + MCHPCOREPWM_PERIOD);

	state->period = (period_steps + 1) * (prescale + 1);
	state->period *= NSEC_PER_SEC;
	state->period = DIV64_U64_ROUND_UP(state->period, rate);

	posedge = readb_relaxed(mchp_core_pwm->base + MCHPCOREPWM_POSEDGE(pwm->hwpwm));
	negedge = readb_relaxed(mchp_core_pwm->base + MCHPCOREPWM_NEGEDGE(pwm->hwpwm));

	mutex_unlock(&mchp_core_pwm->lock);

	if (negedge == posedge) {
	state->duty_cycle = state->period;
	state->period *= 2;
	} else {
	duty_steps = abs((s16)posedge - (s16)negedge);
	state->duty_cycle = duty_steps * (prescale + 1) * NSEC_PER_SEC;
	state->duty_cycle = DIV64_U64_ROUND_UP(state->duty_cycle, rate);
	}

	state->polarity = negedge < posedge ? PWM_POLARITY_INVERSED : PWM_POLARITY_NORMAL;

	return 0;
	}

	static const struct pwm_ops mchp_core_pwm_ops = {
	.apply = mchp_core_pwm_apply,
	.get_state = mchp_core_pwm_get_state,
	.owner = THIS_MODULE,
	};

	static const struct of_device_id mchp_core_of_match[] = {
	{
	.compatible = "microchip,corepwm-rtl-v4",
	},
	{ /* sentinel */ }
	};
	MODULE_DEVICE_TABLE(of, mchp_core_of_match);

	static int mchp_core_pwm_probe(struct platform_device *pdev)
	{
	struct mchp_core_pwm_chip *mchp_core_pwm;
	struct resource *regs;
	int ret;

	mchp_core_pwm = devm_kzalloc(&pdev->dev, sizeof(*mchp_core_pwm), GFP_KERNEL);
	if (!mchp_core_pwm)
	return -ENOMEM;

	mchp_core_pwm->base = devm_platform_get_and_ioremap_resource(pdev, 0, &regs);
	if (IS_ERR(mchp_core_pwm->base))
	return PTR_ERR(mchp_core_pwm->base);

	mchp_core_pwm->clk = devm_clk_get_enabled(&pdev->dev, NULL);
	if (IS_ERR(mchp_core_pwm->clk))
	return dev_err_probe(&pdev->dev, PTR_ERR(mchp_core_pwm->clk),
	"failed to get PWM clock\n");

	if (of_property_read_u32(pdev->dev.of_node, "microchip,sync-update-mask",
	&mchp_core_pwm->sync_update_mask))
	mchp_core_pwm->sync_update_mask = 0;

	mutex_init(&mchp_core_pwm->lock);

	mchp_core_pwm->chip.dev = &pdev->dev;
	mchp_core_pwm->chip.ops = &mchp_core_pwm_ops;
	mchp_core_pwm->chip.npwm = 16;

	mchp_core_pwm->channel_enabled = readb_relaxed(mchp_core_pwm->base + MCHPCOREPWM_EN(0));
	mchp_core_pwm->channel_enabled \|=
	readb_relaxed(mchp_core_pwm->base + MCHPCOREPWM_EN(1)) << 8;

	/*
	* Enable synchronous update mode for all channels for which shadow
	* registers have been synthesised.
	*/
	writel_relaxed(1U, mchp_core_pwm->base + MCHPCOREPWM_SYNC_UPD);
	mchp_core_pwm->update_timestamp = ktime_get();

	ret = devm_pwmchip_add(&pdev->dev, &mchp_core_pwm->chip);
	if (ret)
	return dev_err_probe(&pdev->dev, ret, "Failed to add pwmchip\n");

	return 0;
	}

	static struct platform_driver mchp_core_pwm_driver = {
	.driver = {
	.name = "mchp-core-pwm",
	.of_match_table = mchp_core_of_match,
	},
	.probe = mchp_core_pwm_probe,
	};
	module_platform_driver(mchp_core_pwm_driver);

	MODULE_LICENSE("GPL");
	MODULE_AUTHOR("Conor Dooley <conor.dooley@microchip.com>");
	MODULE_DESCRIPTION("corePWM driver for Microchip FPGAs");