diff options
Diffstat (limited to 'drivers/pwm/pwm-microchip-core.c')
| -rw-r--r-- | drivers/pwm/pwm-microchip-core.c | 507 |
1 files changed, 507 insertions, 0 deletions
diff --git a/drivers/pwm/pwm-microchip-core.c b/drivers/pwm/pwm-microchip-core.c new file mode 100644 index 000000000000..8750b57684a9 --- /dev/null +++ b/drivers/pwm/pwm-microchip-core.c @@ -0,0 +1,507 @@ +// 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"); |