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// SPDX-License-Identifier: GPL-2.0
/*
* Clock based PWM controller
*
* Copyright (c) 2021 Nikita Travkin <nikita@trvn.ru>
*
* This is an "adapter" driver that allows PWM consumers to use
* system clocks with duty cycle control as PWM outputs.
*
* Limitations:
* - Due to the fact that exact behavior depends on the underlying
* clock driver, various limitations are possible.
* - Underlying clock may not be able to give 0% or 100% duty cycle
* (constant off or on), exact behavior will depend on the clock.
* - When the PWM is disabled, the clock will be disabled as well,
* line state will depend on the clock.
* - The clk API doesn't expose the necessary calls to implement
* .get_state().
*/
#include <linux/kernel.h>
#include <linux/math64.h>
#include <linux/err.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/platform_device.h>
#include <linux/clk.h>
#include <linux/pwm.h>
struct pwm_clk_chip {
struct clk *clk;
bool clk_enabled;
};
static inline struct pwm_clk_chip *to_pwm_clk_chip(struct pwm_chip *chip)
{
return pwmchip_get_drvdata(chip);
}
static int pwm_clk_apply(struct pwm_chip *chip, struct pwm_device *pwm,
const struct pwm_state *state)
{
struct pwm_clk_chip *pcchip = to_pwm_clk_chip(chip);
int ret;
u32 rate;
u64 period = state->period;
u64 duty_cycle = state->duty_cycle;
if (!state->enabled) {
if (pwm->state.enabled) {
clk_disable(pcchip->clk);
pcchip->clk_enabled = false;
}
return 0;
} else if (!pwm->state.enabled) {
ret = clk_enable(pcchip->clk);
if (ret)
return ret;
pcchip->clk_enabled = true;
}
/*
* We have to enable the clk before setting the rate and duty_cycle,
* that however results in a window where the clk is on with a
* (potentially) different setting. Also setting period and duty_cycle
* are two separate calls, so that probably isn't atomic either.
*/
rate = DIV64_U64_ROUND_UP(NSEC_PER_SEC, period);
ret = clk_set_rate(pcchip->clk, rate);
if (ret)
return ret;
if (state->polarity == PWM_POLARITY_INVERSED)
duty_cycle = period - duty_cycle;
return clk_set_duty_cycle(pcchip->clk, duty_cycle, period);
}
static const struct pwm_ops pwm_clk_ops = {
.apply = pwm_clk_apply,
};
static int pwm_clk_probe(struct platform_device *pdev)
{
struct pwm_chip *chip;
struct pwm_clk_chip *pcchip;
int ret;
chip = devm_pwmchip_alloc(&pdev->dev, 1, sizeof(*pcchip));
if (IS_ERR(chip))
return PTR_ERR(chip);
pcchip = to_pwm_clk_chip(chip);
pcchip->clk = devm_clk_get_prepared(&pdev->dev, NULL);
if (IS_ERR(pcchip->clk))
return dev_err_probe(&pdev->dev, PTR_ERR(pcchip->clk),
"Failed to get clock\n");
chip->ops = &pwm_clk_ops;
ret = pwmchip_add(chip);
if (ret < 0)
return dev_err_probe(&pdev->dev, ret, "Failed to add pwm chip\n");
platform_set_drvdata(pdev, chip);
return 0;
}
static void pwm_clk_remove(struct platform_device *pdev)
{
struct pwm_chip *chip = platform_get_drvdata(pdev);
struct pwm_clk_chip *pcchip = to_pwm_clk_chip(chip);
pwmchip_remove(chip);
if (pcchip->clk_enabled)
clk_disable(pcchip->clk);
}
static const struct of_device_id pwm_clk_dt_ids[] = {
{ .compatible = "clk-pwm", },
{ /* sentinel */ }
};
MODULE_DEVICE_TABLE(of, pwm_clk_dt_ids);
static struct platform_driver pwm_clk_driver = {
.driver = {
.name = "pwm-clk",
.of_match_table = pwm_clk_dt_ids,
},
.probe = pwm_clk_probe,
.remove = pwm_clk_remove,
};
module_platform_driver(pwm_clk_driver);
MODULE_ALIAS("platform:pwm-clk");
MODULE_AUTHOR("Nikita Travkin <nikita@trvn.ru>");
MODULE_DESCRIPTION("Clock based PWM driver");
MODULE_LICENSE("GPL");
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