f9a8ee8c8b
Since commit 5e5da1e9fb ("pwm: ab8500: Explicitly allocate pwm chip
base dynamically") all drivers use dynamic ID allocation explicitly. New
drivers are supposed to do the same, so remove support for driver
specified base IDs and drop all assignments in the low-level drivers.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
272 lines
8.5 KiB
C
272 lines
8.5 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* sl28cpld PWM driver
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*
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* Copyright (c) 2020 Michael Walle <michael@walle.cc>
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*
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* There is no public datasheet available for this PWM core. But it is easy
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* enough to be briefly explained. It consists of one 8-bit counter. The PWM
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* supports four distinct frequencies by selecting when to reset the counter.
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* With the prescaler setting you can select which bit of the counter is used
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* to reset it. This implies that the higher the frequency the less remaining
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* bits are available for the actual counter.
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*
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* Let cnt[7:0] be the counter, clocked at 32kHz:
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* +-----------+--------+--------------+-----------+---------------+
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* | prescaler | reset | counter bits | frequency | period length |
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* +-----------+--------+--------------+-----------+---------------+
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* | 0 | cnt[7] | cnt[6:0] | 250 Hz | 4000000 ns |
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* | 1 | cnt[6] | cnt[5:0] | 500 Hz | 2000000 ns |
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* | 2 | cnt[5] | cnt[4:0] | 1 kHz | 1000000 ns |
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* | 3 | cnt[4] | cnt[3:0] | 2 kHz | 500000 ns |
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* +-----------+--------+--------------+-----------+---------------+
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*
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* Limitations:
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* - The hardware cannot generate a 100% duty cycle if the prescaler is 0.
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* - The hardware cannot atomically set the prescaler and the counter value,
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* which might lead to glitches and inconsistent states if a write fails.
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* - The counter is not reset if you switch the prescaler which leads
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* to glitches, too.
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* - The duty cycle will switch immediately and not after a complete cycle.
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* - Depending on the actual implementation, disabling the PWM might have
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* side effects. For example, if the output pin is shared with a GPIO pin
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* it will automatically switch back to GPIO mode.
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*/
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#include <linux/bitfield.h>
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#include <linux/kernel.h>
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#include <linux/mod_devicetable.h>
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#include <linux/module.h>
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#include <linux/platform_device.h>
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#include <linux/pwm.h>
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#include <linux/regmap.h>
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/*
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* PWM timer block registers.
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*/
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#define SL28CPLD_PWM_CTRL 0x00
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#define SL28CPLD_PWM_CTRL_ENABLE BIT(7)
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#define SL28CPLD_PWM_CTRL_PRESCALER_MASK GENMASK(1, 0)
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#define SL28CPLD_PWM_CYCLE 0x01
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#define SL28CPLD_PWM_CYCLE_MAX GENMASK(6, 0)
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#define SL28CPLD_PWM_CLK 32000 /* 32 kHz */
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#define SL28CPLD_PWM_MAX_DUTY_CYCLE(prescaler) (1 << (7 - (prescaler)))
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#define SL28CPLD_PWM_PERIOD(prescaler) \
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(NSEC_PER_SEC / SL28CPLD_PWM_CLK * SL28CPLD_PWM_MAX_DUTY_CYCLE(prescaler))
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/*
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* We calculate the duty cycle like this:
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* duty_cycle_ns = pwm_cycle_reg * max_period_ns / max_duty_cycle
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*
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* With
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* max_period_ns = 1 << (7 - prescaler) / SL28CPLD_PWM_CLK * NSEC_PER_SEC
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* max_duty_cycle = 1 << (7 - prescaler)
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* this then simplifies to:
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* duty_cycle_ns = pwm_cycle_reg / SL28CPLD_PWM_CLK * NSEC_PER_SEC
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* = NSEC_PER_SEC / SL28CPLD_PWM_CLK * pwm_cycle_reg
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*
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* NSEC_PER_SEC is a multiple of SL28CPLD_PWM_CLK, therefore we're not losing
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* precision by doing the divison first.
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*/
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#define SL28CPLD_PWM_TO_DUTY_CYCLE(reg) \
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(NSEC_PER_SEC / SL28CPLD_PWM_CLK * (reg))
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#define SL28CPLD_PWM_FROM_DUTY_CYCLE(duty_cycle) \
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(DIV_ROUND_DOWN_ULL((duty_cycle), NSEC_PER_SEC / SL28CPLD_PWM_CLK))
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#define sl28cpld_pwm_read(priv, reg, val) \
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regmap_read((priv)->regmap, (priv)->offset + (reg), (val))
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#define sl28cpld_pwm_write(priv, reg, val) \
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regmap_write((priv)->regmap, (priv)->offset + (reg), (val))
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struct sl28cpld_pwm {
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struct pwm_chip pwm_chip;
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struct regmap *regmap;
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u32 offset;
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};
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#define sl28cpld_pwm_from_chip(_chip) \
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container_of(_chip, struct sl28cpld_pwm, pwm_chip)
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static void sl28cpld_pwm_get_state(struct pwm_chip *chip,
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struct pwm_device *pwm,
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struct pwm_state *state)
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{
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struct sl28cpld_pwm *priv = sl28cpld_pwm_from_chip(chip);
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unsigned int reg;
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int prescaler;
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sl28cpld_pwm_read(priv, SL28CPLD_PWM_CTRL, ®);
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state->enabled = reg & SL28CPLD_PWM_CTRL_ENABLE;
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prescaler = FIELD_GET(SL28CPLD_PWM_CTRL_PRESCALER_MASK, reg);
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state->period = SL28CPLD_PWM_PERIOD(prescaler);
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sl28cpld_pwm_read(priv, SL28CPLD_PWM_CYCLE, ®);
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state->duty_cycle = SL28CPLD_PWM_TO_DUTY_CYCLE(reg);
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state->polarity = PWM_POLARITY_NORMAL;
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/*
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* Sanitize values for the PWM core. Depending on the prescaler it
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* might happen that we calculate a duty_cycle greater than the actual
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* period. This might happen if someone (e.g. the bootloader) sets an
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* invalid combination of values. The behavior of the hardware is
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* undefined in this case. But we need to report sane values back to
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* the PWM core.
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*/
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state->duty_cycle = min(state->duty_cycle, state->period);
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}
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static int sl28cpld_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
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const struct pwm_state *state)
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{
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struct sl28cpld_pwm *priv = sl28cpld_pwm_from_chip(chip);
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unsigned int cycle, prescaler;
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bool write_duty_cycle_first;
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int ret;
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u8 ctrl;
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/* Polarity inversion is not supported */
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if (state->polarity != PWM_POLARITY_NORMAL)
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return -EINVAL;
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/*
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* Calculate the prescaler. Pick the biggest period that isn't
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* bigger than the requested period.
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*/
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prescaler = DIV_ROUND_UP_ULL(SL28CPLD_PWM_PERIOD(0), state->period);
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prescaler = order_base_2(prescaler);
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if (prescaler > field_max(SL28CPLD_PWM_CTRL_PRESCALER_MASK))
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return -ERANGE;
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ctrl = FIELD_PREP(SL28CPLD_PWM_CTRL_PRESCALER_MASK, prescaler);
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if (state->enabled)
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ctrl |= SL28CPLD_PWM_CTRL_ENABLE;
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cycle = SL28CPLD_PWM_FROM_DUTY_CYCLE(state->duty_cycle);
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cycle = min_t(unsigned int, cycle, SL28CPLD_PWM_MAX_DUTY_CYCLE(prescaler));
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/*
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* Work around the hardware limitation. See also above. Trap 100% duty
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* cycle if the prescaler is 0. Set prescaler to 1 instead. We don't
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* care about the frequency because its "all-one" in either case.
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*
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* We don't need to check the actual prescaler setting, because only
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* if the prescaler is 0 we can have this particular value.
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*/
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if (cycle == SL28CPLD_PWM_MAX_DUTY_CYCLE(0)) {
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ctrl &= ~SL28CPLD_PWM_CTRL_PRESCALER_MASK;
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ctrl |= FIELD_PREP(SL28CPLD_PWM_CTRL_PRESCALER_MASK, 1);
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cycle = SL28CPLD_PWM_MAX_DUTY_CYCLE(1);
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}
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/*
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* To avoid glitches when we switch the prescaler, we have to make sure
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* we have a valid duty cycle for the new mode.
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*
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* Take the current prescaler (or the current period length) into
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* account to decide whether we have to write the duty cycle or the new
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* prescaler first. If the period length is decreasing we have to
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* write the duty cycle first.
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*/
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write_duty_cycle_first = pwm->state.period > state->period;
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if (write_duty_cycle_first) {
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ret = sl28cpld_pwm_write(priv, SL28CPLD_PWM_CYCLE, cycle);
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if (ret)
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return ret;
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}
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ret = sl28cpld_pwm_write(priv, SL28CPLD_PWM_CTRL, ctrl);
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if (ret)
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return ret;
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if (!write_duty_cycle_first) {
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ret = sl28cpld_pwm_write(priv, SL28CPLD_PWM_CYCLE, cycle);
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if (ret)
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return ret;
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}
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return 0;
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}
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static const struct pwm_ops sl28cpld_pwm_ops = {
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.apply = sl28cpld_pwm_apply,
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.get_state = sl28cpld_pwm_get_state,
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.owner = THIS_MODULE,
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};
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static int sl28cpld_pwm_probe(struct platform_device *pdev)
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{
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struct sl28cpld_pwm *priv;
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struct pwm_chip *chip;
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int ret;
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if (!pdev->dev.parent) {
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dev_err(&pdev->dev, "no parent device\n");
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return -ENODEV;
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}
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priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
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if (!priv)
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return -ENOMEM;
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priv->regmap = dev_get_regmap(pdev->dev.parent, NULL);
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if (!priv->regmap) {
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dev_err(&pdev->dev, "could not get parent regmap\n");
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return -ENODEV;
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}
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ret = device_property_read_u32(&pdev->dev, "reg", &priv->offset);
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if (ret) {
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dev_err(&pdev->dev, "no 'reg' property found (%pe)\n",
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ERR_PTR(ret));
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return -EINVAL;
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}
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/* Initialize the pwm_chip structure */
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chip = &priv->pwm_chip;
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chip->dev = &pdev->dev;
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chip->ops = &sl28cpld_pwm_ops;
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chip->npwm = 1;
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platform_set_drvdata(pdev, priv);
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ret = pwmchip_add(&priv->pwm_chip);
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if (ret) {
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dev_err(&pdev->dev, "failed to add PWM chip (%pe)",
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ERR_PTR(ret));
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return ret;
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}
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return 0;
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}
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static int sl28cpld_pwm_remove(struct platform_device *pdev)
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{
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struct sl28cpld_pwm *priv = platform_get_drvdata(pdev);
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return pwmchip_remove(&priv->pwm_chip);
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}
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static const struct of_device_id sl28cpld_pwm_of_match[] = {
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{ .compatible = "kontron,sl28cpld-pwm" },
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{}
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};
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MODULE_DEVICE_TABLE(of, sl28cpld_pwm_of_match);
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static struct platform_driver sl28cpld_pwm_driver = {
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.probe = sl28cpld_pwm_probe,
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.remove = sl28cpld_pwm_remove,
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.driver = {
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.name = "sl28cpld-pwm",
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.of_match_table = sl28cpld_pwm_of_match,
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},
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};
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module_platform_driver(sl28cpld_pwm_driver);
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MODULE_DESCRIPTION("sl28cpld PWM Driver");
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MODULE_AUTHOR("Michael Walle <michael@walle.cc>");
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MODULE_LICENSE("GPL");
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