diff options
Diffstat (limited to 'drivers/pwm/pwm-clk.c')
| -rw-r--r-- | drivers/pwm/pwm-clk.c | 148 |
1 files changed, 148 insertions, 0 deletions
diff --git a/drivers/pwm/pwm-clk.c b/drivers/pwm/pwm-clk.c new file mode 100644 index 000000000..c2a503d68 --- /dev/null +++ b/drivers/pwm/pwm-clk.c @@ -0,0 +1,148 @@ +// 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 pwm_chip chip; + struct clk *clk; + bool clk_enabled; +}; + +#define to_pwm_clk_chip(_chip) container_of(_chip, struct pwm_clk_chip, 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, + .owner = THIS_MODULE, +}; + +static int pwm_clk_probe(struct platform_device *pdev) +{ + struct pwm_clk_chip *pcchip; + int ret; + + pcchip = devm_kzalloc(&pdev->dev, sizeof(*pcchip), GFP_KERNEL); + if (!pcchip) + return -ENOMEM; + + pcchip->clk = devm_clk_get(&pdev->dev, NULL); + if (IS_ERR(pcchip->clk)) + return dev_err_probe(&pdev->dev, PTR_ERR(pcchip->clk), + "Failed to get clock\n"); + + pcchip->chip.dev = &pdev->dev; + pcchip->chip.ops = &pwm_clk_ops; + pcchip->chip.npwm = 1; + + ret = clk_prepare(pcchip->clk); + if (ret < 0) + return dev_err_probe(&pdev->dev, ret, "Failed to prepare clock\n"); + + ret = pwmchip_add(&pcchip->chip); + if (ret < 0) { + clk_unprepare(pcchip->clk); + return dev_err_probe(&pdev->dev, ret, "Failed to add pwm chip\n"); + } + + platform_set_drvdata(pdev, pcchip); + return 0; +} + +static int pwm_clk_remove(struct platform_device *pdev) +{ + struct pwm_clk_chip *pcchip = platform_get_drvdata(pdev); + + pwmchip_remove(&pcchip->chip); + + if (pcchip->clk_enabled) + clk_disable(pcchip->clk); + + clk_unprepare(pcchip->clk); + + return 0; +} + +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"); |