diff options
Diffstat (limited to 'drivers/pwm/pwm-sl28cpld.c')
| -rw-r--r-- | drivers/pwm/pwm-sl28cpld.c | 267 |
1 files changed, 267 insertions, 0 deletions
diff --git a/drivers/pwm/pwm-sl28cpld.c b/drivers/pwm/pwm-sl28cpld.c new file mode 100644 index 0000000000..9e42e3a74a --- /dev/null +++ b/drivers/pwm/pwm-sl28cpld.c @@ -0,0 +1,267 @@ +// 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 pwm_chip chip; + struct regmap *regmap; + u32 offset; +}; + +static inline struct sl28cpld_pwm *sl28cpld_pwm_from_chip(struct pwm_chip *chip) +{ + return container_of(chip, struct sl28cpld_pwm, 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, ®); + + 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, ®); + 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, + .owner = THIS_MODULE, +}; + +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; + } + + priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL); + if (!priv) + return -ENOMEM; + + 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 = &priv->chip; + chip->dev = &pdev->dev; + chip->ops = &sl28cpld_pwm_ops; + chip->npwm = 1; + + 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"); |