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![Uwe Kleine-König](/assets/img/avatar_default.png)
Compared to overwriting pdev->dev.of_node directly, this takes care of
reference counting. It also prevents that the parent device matches this
driver. See commit 9b22c17a3c
("of: Check 'of_node_reused' flag on
of_match_device()") for further details.
Suggested-by: Rob Herring <robh@kernel.org>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
170 lines
4.9 KiB
C
170 lines
4.9 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* The Netronix embedded controller is a microcontroller found in some
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* e-book readers designed by the original design manufacturer Netronix, Inc.
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* It contains RTC, battery monitoring, system power management, and PWM
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* functionality.
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*
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* This driver implements PWM output.
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*
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* Copyright 2020 Jonathan Neuschäfer <j.neuschaefer@gmx.net>
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*
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* Limitations:
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* - The get_state callback is not implemented, because the current state of
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* the PWM output can't be read back from the hardware.
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* - The hardware can only generate normal polarity output.
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* - The period and duty cycle can't be changed together in one atomic action.
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*/
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#include <linux/mfd/ntxec.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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#include <linux/types.h>
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struct ntxec_pwm {
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struct ntxec *ec;
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struct pwm_chip chip;
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};
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static struct ntxec_pwm *ntxec_pwm_from_chip(struct pwm_chip *chip)
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{
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return container_of(chip, struct ntxec_pwm, chip);
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}
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#define NTXEC_REG_AUTO_OFF_HI 0xa1
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#define NTXEC_REG_AUTO_OFF_LO 0xa2
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#define NTXEC_REG_ENABLE 0xa3
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#define NTXEC_REG_PERIOD_LOW 0xa4
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#define NTXEC_REG_PERIOD_HIGH 0xa5
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#define NTXEC_REG_DUTY_LOW 0xa6
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#define NTXEC_REG_DUTY_HIGH 0xa7
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/*
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* The time base used in the EC is 8MHz, or 125ns. Period and duty cycle are
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* measured in this unit.
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*/
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#define TIME_BASE_NS 125
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/*
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* The maximum input value (in nanoseconds) is determined by the time base and
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* the range of the hardware registers that hold the converted value.
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* It fits into 32 bits, so we can do our calculations in 32 bits as well.
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*/
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#define MAX_PERIOD_NS (TIME_BASE_NS * 0xffff)
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static int ntxec_pwm_set_raw_period_and_duty_cycle(struct pwm_chip *chip,
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int period, int duty)
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{
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struct ntxec_pwm *priv = ntxec_pwm_from_chip(chip);
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/*
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* Changes to the period and duty cycle take effect as soon as the
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* corresponding low byte is written, so the hardware may be configured
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* to an inconsistent state after the period is written and before the
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* duty cycle is fully written. If, in such a case, the old duty cycle
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* is longer than the new period, the EC may output 100% for a moment.
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*
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* To minimize the time between the changes to period and duty cycle
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* taking effect, the writes are interleaved.
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*/
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struct reg_sequence regs[] = {
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{ NTXEC_REG_PERIOD_HIGH, ntxec_reg8(period >> 8) },
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{ NTXEC_REG_DUTY_HIGH, ntxec_reg8(duty >> 8) },
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{ NTXEC_REG_PERIOD_LOW, ntxec_reg8(period) },
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{ NTXEC_REG_DUTY_LOW, ntxec_reg8(duty) },
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};
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return regmap_multi_reg_write(priv->ec->regmap, regs, ARRAY_SIZE(regs));
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}
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static int ntxec_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm_dev,
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const struct pwm_state *state)
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{
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struct ntxec_pwm *priv = ntxec_pwm_from_chip(chip);
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unsigned int period, duty;
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int res;
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if (state->polarity != PWM_POLARITY_NORMAL)
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return -EINVAL;
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period = min_t(u64, state->period, MAX_PERIOD_NS);
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duty = min_t(u64, state->duty_cycle, period);
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period /= TIME_BASE_NS;
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duty /= TIME_BASE_NS;
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/*
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* Writing a duty cycle of zero puts the device into a state where
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* writing a higher duty cycle doesn't result in the brightness that it
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* usually results in. This can be fixed by cycling the ENABLE register.
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*
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* As a workaround, write ENABLE=0 when the duty cycle is zero.
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* The case that something has previously set the duty cycle to zero
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* but ENABLE=1, is not handled.
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*/
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if (state->enabled && duty != 0) {
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res = ntxec_pwm_set_raw_period_and_duty_cycle(chip, period, duty);
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if (res)
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return res;
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res = regmap_write(priv->ec->regmap, NTXEC_REG_ENABLE, ntxec_reg8(1));
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if (res)
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return res;
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/* Disable the auto-off timer */
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res = regmap_write(priv->ec->regmap, NTXEC_REG_AUTO_OFF_HI, ntxec_reg8(0xff));
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if (res)
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return res;
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return regmap_write(priv->ec->regmap, NTXEC_REG_AUTO_OFF_LO, ntxec_reg8(0xff));
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} else {
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return regmap_write(priv->ec->regmap, NTXEC_REG_ENABLE, ntxec_reg8(0));
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}
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}
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static const struct pwm_ops ntxec_pwm_ops = {
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.owner = THIS_MODULE,
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.apply = ntxec_pwm_apply,
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/*
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* No .get_state callback, because the current state cannot be read
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* back from the hardware.
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*/
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};
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static int ntxec_pwm_probe(struct platform_device *pdev)
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{
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struct ntxec *ec = dev_get_drvdata(pdev->dev.parent);
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struct ntxec_pwm *priv;
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struct pwm_chip *chip;
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device_set_of_node_from_dev(&pdev->dev, pdev->dev.parent);
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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->ec = ec;
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chip = &priv->chip;
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chip->dev = &pdev->dev;
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chip->ops = &ntxec_pwm_ops;
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chip->npwm = 1;
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return devm_pwmchip_add(&pdev->dev, chip);
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}
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static struct platform_driver ntxec_pwm_driver = {
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.driver = {
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.name = "ntxec-pwm",
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},
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.probe = ntxec_pwm_probe,
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};
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module_platform_driver(ntxec_pwm_driver);
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MODULE_AUTHOR("Jonathan Neuschäfer <j.neuschaefer@gmx.net>");
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MODULE_DESCRIPTION("PWM driver for Netronix EC");
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MODULE_LICENSE("GPL");
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MODULE_ALIAS("platform:ntxec-pwm");
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