--- /dev/null
+// 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_device.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, ®s);
+ 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");
projects / platform / kernel / linux-starfive.git / commitdiff