// 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/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 pwm_chip;
struct regmap *regmap;
u32 offset;
};
#define sl28cpld_pwm_from_chip(_chip) \
container_of(_chip, struct sl28cpld_pwm, 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->pwm_chip;
chip->dev = &pdev->dev;
chip->ops = &sl28cpld_pwm_ops;
chip->npwm = 1;
ret = devm_pwmchip_add(&pdev->dev, &priv->pwm_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");
