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![Jeff LaBundy](/assets/img/avatar_default.png)
If duty cycle is first set to a value that is sufficiently high to enable the output (e.g. 10000 ns) but then lowered to a value that is quantized to zero (e.g. 1000 ns), the output is disabled as the device cannot drive a constant zero (as expected). However if the device is later re-initialized due to watchdog bite, the output is re-enabled at the next-to-last duty cycle (10000 ns). This is because the iqs620_pwm->out_en flag unconditionally tracks state->enabled instead of what was actually written to the device. To solve this problem, use one state variable that encodes all 257 states of the output (duty_scale) with 0 representing tri-state, 1 representing the minimum available duty cycle and 256 representing 100% duty cycle. Signed-off-by: Jeff LaBundy <jeff@labundy.com> Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de> Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
259 lines
6.7 KiB
C
259 lines
6.7 KiB
C
// SPDX-License-Identifier: GPL-2.0+
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/*
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* Azoteq IQS620A PWM Generator
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*
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* Copyright (C) 2019 Jeff LaBundy <jeff@labundy.com>
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*
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* Limitations:
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* - The period is fixed to 1 ms and is generated continuously despite changes
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* to the duty cycle or enable/disable state.
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* - Changes to the duty cycle or enable/disable state take effect immediately
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* and may result in a glitch during the period in which the change is made.
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* - The device cannot generate a 0% duty cycle. For duty cycles below 1 / 256
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* ms, the output is disabled and relies upon an external pull-down resistor
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* to hold the GPIO3/LTX pin low.
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*/
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#include <linux/device.h>
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#include <linux/kernel.h>
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#include <linux/mfd/iqs62x.h>
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#include <linux/module.h>
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#include <linux/mutex.h>
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#include <linux/notifier.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/slab.h>
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#define IQS620_PWR_SETTINGS 0xd2
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#define IQS620_PWR_SETTINGS_PWM_OUT BIT(7)
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#define IQS620_PWM_DUTY_CYCLE 0xd8
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#define IQS620_PWM_PERIOD_NS 1000000
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struct iqs620_pwm_private {
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struct iqs62x_core *iqs62x;
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struct pwm_chip chip;
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struct notifier_block notifier;
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struct mutex lock;
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unsigned int duty_scale;
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};
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static int iqs620_pwm_init(struct iqs620_pwm_private *iqs620_pwm,
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unsigned int duty_scale)
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{
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struct iqs62x_core *iqs62x = iqs620_pwm->iqs62x;
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int ret;
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if (!duty_scale)
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return regmap_update_bits(iqs62x->regmap, IQS620_PWR_SETTINGS,
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IQS620_PWR_SETTINGS_PWM_OUT, 0);
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ret = regmap_write(iqs62x->regmap, IQS620_PWM_DUTY_CYCLE,
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duty_scale - 1);
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if (ret)
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return ret;
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return regmap_update_bits(iqs62x->regmap, IQS620_PWR_SETTINGS,
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IQS620_PWR_SETTINGS_PWM_OUT, 0xff);
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}
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static int iqs620_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 iqs620_pwm_private *iqs620_pwm;
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unsigned int duty_cycle;
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unsigned int duty_scale;
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int ret;
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if (state->polarity != PWM_POLARITY_NORMAL)
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return -EINVAL;
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if (state->period < IQS620_PWM_PERIOD_NS)
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return -EINVAL;
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iqs620_pwm = container_of(chip, struct iqs620_pwm_private, chip);
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/*
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* The duty cycle generated by the device is calculated as follows:
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*
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* duty_cycle = (IQS620_PWM_DUTY_CYCLE + 1) / 256 * 1 ms
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*
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* ...where IQS620_PWM_DUTY_CYCLE is a register value between 0 and 255
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* (inclusive). Therefore the lowest duty cycle the device can generate
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* while the output is enabled is 1 / 256 ms.
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*
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* For lower duty cycles (e.g. 0), the PWM output is simply disabled to
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* allow an external pull-down resistor to hold the GPIO3/LTX pin low.
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*/
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duty_cycle = min_t(u64, state->duty_cycle, IQS620_PWM_PERIOD_NS);
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duty_scale = duty_cycle * 256 / IQS620_PWM_PERIOD_NS;
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if (!state->enabled)
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duty_scale = 0;
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mutex_lock(&iqs620_pwm->lock);
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ret = iqs620_pwm_init(iqs620_pwm, duty_scale);
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if (!ret)
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iqs620_pwm->duty_scale = duty_scale;
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mutex_unlock(&iqs620_pwm->lock);
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return ret;
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}
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static void iqs620_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
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struct pwm_state *state)
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{
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struct iqs620_pwm_private *iqs620_pwm;
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iqs620_pwm = container_of(chip, struct iqs620_pwm_private, chip);
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mutex_lock(&iqs620_pwm->lock);
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/*
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* Since the device cannot generate a 0% duty cycle, requests to do so
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* cause subsequent calls to iqs620_pwm_get_state to report the output
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* as disabled. This is not ideal, but is the best compromise based on
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* the capabilities of the device.
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*/
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state->enabled = iqs620_pwm->duty_scale > 0;
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state->duty_cycle = DIV_ROUND_UP(iqs620_pwm->duty_scale *
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IQS620_PWM_PERIOD_NS, 256);
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mutex_unlock(&iqs620_pwm->lock);
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state->period = IQS620_PWM_PERIOD_NS;
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}
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static int iqs620_pwm_notifier(struct notifier_block *notifier,
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unsigned long event_flags, void *context)
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{
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struct iqs620_pwm_private *iqs620_pwm;
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int ret;
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if (!(event_flags & BIT(IQS62X_EVENT_SYS_RESET)))
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return NOTIFY_DONE;
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iqs620_pwm = container_of(notifier, struct iqs620_pwm_private,
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notifier);
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mutex_lock(&iqs620_pwm->lock);
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/*
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* The parent MFD driver already prints an error message in the event
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* of a device reset, so nothing else is printed here unless there is
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* an additional failure.
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*/
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ret = iqs620_pwm_init(iqs620_pwm, iqs620_pwm->duty_scale);
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mutex_unlock(&iqs620_pwm->lock);
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if (ret) {
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dev_err(iqs620_pwm->chip.dev,
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"Failed to re-initialize device: %d\n", ret);
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return NOTIFY_BAD;
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}
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return NOTIFY_OK;
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}
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static const struct pwm_ops iqs620_pwm_ops = {
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.apply = iqs620_pwm_apply,
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.get_state = iqs620_pwm_get_state,
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.owner = THIS_MODULE,
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};
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static void iqs620_pwm_notifier_unregister(void *context)
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{
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struct iqs620_pwm_private *iqs620_pwm = context;
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int ret;
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ret = blocking_notifier_chain_unregister(&iqs620_pwm->iqs62x->nh,
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&iqs620_pwm->notifier);
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if (ret)
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dev_err(iqs620_pwm->chip.dev,
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"Failed to unregister notifier: %d\n", ret);
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}
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static int iqs620_pwm_probe(struct platform_device *pdev)
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{
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struct iqs62x_core *iqs62x = dev_get_drvdata(pdev->dev.parent);
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struct iqs620_pwm_private *iqs620_pwm;
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unsigned int val;
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int ret;
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iqs620_pwm = devm_kzalloc(&pdev->dev, sizeof(*iqs620_pwm), GFP_KERNEL);
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if (!iqs620_pwm)
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return -ENOMEM;
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platform_set_drvdata(pdev, iqs620_pwm);
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iqs620_pwm->iqs62x = iqs62x;
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ret = regmap_read(iqs62x->regmap, IQS620_PWR_SETTINGS, &val);
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if (ret)
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return ret;
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if (val & IQS620_PWR_SETTINGS_PWM_OUT) {
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ret = regmap_read(iqs62x->regmap, IQS620_PWM_DUTY_CYCLE, &val);
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if (ret)
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return ret;
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iqs620_pwm->duty_scale = val + 1;
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}
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iqs620_pwm->chip.dev = &pdev->dev;
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iqs620_pwm->chip.ops = &iqs620_pwm_ops;
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iqs620_pwm->chip.base = -1;
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iqs620_pwm->chip.npwm = 1;
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mutex_init(&iqs620_pwm->lock);
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iqs620_pwm->notifier.notifier_call = iqs620_pwm_notifier;
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ret = blocking_notifier_chain_register(&iqs620_pwm->iqs62x->nh,
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&iqs620_pwm->notifier);
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if (ret) {
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dev_err(&pdev->dev, "Failed to register notifier: %d\n", ret);
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return ret;
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}
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ret = devm_add_action_or_reset(&pdev->dev,
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iqs620_pwm_notifier_unregister,
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iqs620_pwm);
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if (ret)
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return ret;
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ret = pwmchip_add(&iqs620_pwm->chip);
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if (ret)
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dev_err(&pdev->dev, "Failed to add device: %d\n", ret);
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return ret;
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}
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static int iqs620_pwm_remove(struct platform_device *pdev)
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{
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struct iqs620_pwm_private *iqs620_pwm = platform_get_drvdata(pdev);
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int ret;
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ret = pwmchip_remove(&iqs620_pwm->chip);
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if (ret)
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dev_err(&pdev->dev, "Failed to remove device: %d\n", ret);
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return ret;
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}
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static struct platform_driver iqs620_pwm_platform_driver = {
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.driver = {
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.name = "iqs620a-pwm",
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},
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.probe = iqs620_pwm_probe,
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.remove = iqs620_pwm_remove,
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};
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module_platform_driver(iqs620_pwm_platform_driver);
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MODULE_AUTHOR("Jeff LaBundy <jeff@labundy.com>");
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MODULE_DESCRIPTION("Azoteq IQS620A PWM Generator");
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MODULE_LICENSE("GPL");
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MODULE_ALIAS("platform:iqs620a-pwm");
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