drivers/pwm/pwm-clk.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Clock based PWM controller
   4  *
   5  * Copyright (c) 2021 Nikita Travkin <nikita@trvn.ru>
   6  *
   7  * This is an "adapter" driver that allows PWM consumers to use
   8  * system clocks with duty cycle control as PWM outputs.
   9  *
  10  * Limitations:
  11  * - Due to the fact that exact behavior depends on the underlying
  12  *   clock driver, various limitations are possible.
  13  * - Underlying clock may not be able to give 0% or 100% duty cycle
  14  *   (constant off or on), exact behavior will depend on the clock.
  15  * - When the PWM is disabled, the clock will be disabled as well,
  16  *   line state will depend on the clock.
  17  * - The clk API doesn't expose the necessary calls to implement
  18  *   .get_state().
  19  */
  20
  21 #include <linux/kernel.h>
  22 #include <linux/math64.h>
  23 #include <linux/err.h>
  24 #include <linux/module.h>
  25 #include <linux/of.h>
  26 #include <linux/platform_device.h>
  27 #include <linux/clk.h>
  28 #include <linux/pwm.h>
  29
  30 struct pwm_clk_chip {
  31         struct clk *clk;
  32         bool clk_enabled;
  33 };
  34
  35 static inline struct pwm_clk_chip *to_pwm_clk_chip(struct pwm_chip *chip)
  36 {
  37         return pwmchip_get_drvdata(chip);
  38 }
  39
  40 static int pwm_clk_apply(struct pwm_chip *chip, struct pwm_device *pwm,
  41                          const struct pwm_state *state)
  42 {
  43         struct pwm_clk_chip *pcchip = to_pwm_clk_chip(chip);
  44         int ret;
  45         u32 rate;
  46         u64 period = state->period;
  47         u64 duty_cycle = state->duty_cycle;
  48
  49         if (!state->enabled) {
  50                 if (pwm->state.enabled) {
  51                         clk_disable(pcchip->clk);
  52                         pcchip->clk_enabled = false;
  53                 }
  54                 return 0;
  55         } else if (!pwm->state.enabled) {
  56                 ret = clk_enable(pcchip->clk);
  57                 if (ret)
  58                         return ret;
  59                 pcchip->clk_enabled = true;
  60         }
  61
  62         /*
  63          * We have to enable the clk before setting the rate and duty_cycle,
  64          * that however results in a window where the clk is on with a
  65          * (potentially) different setting. Also setting period and duty_cycle
  66          * are two separate calls, so that probably isn't atomic either.
  67          */
  68
  69         rate = DIV64_U64_ROUND_UP(NSEC_PER_SEC, period);
  70         ret = clk_set_rate(pcchip->clk, rate);
  71         if (ret)
  72                 return ret;
  73
  74         if (state->polarity == PWM_POLARITY_INVERSED)
  75                 duty_cycle = period - duty_cycle;
  76
  77         return clk_set_duty_cycle(pcchip->clk, duty_cycle, period);
  78 }
  79
  80 static const struct pwm_ops pwm_clk_ops = {
  81         .apply = pwm_clk_apply,
  82 };
  83
  84 static int pwm_clk_probe(struct platform_device *pdev)
  85 {
  86         struct pwm_chip *chip;
  87         struct pwm_clk_chip *pcchip;
  88         int ret;
  89
  90         chip = devm_pwmchip_alloc(&pdev->dev, 1, sizeof(*pcchip));
  91         if (IS_ERR(chip))
  92                 return PTR_ERR(chip);
  93         pcchip = to_pwm_clk_chip(chip);
  94
  95         pcchip->clk = devm_clk_get_prepared(&pdev->dev, NULL);
  96         if (IS_ERR(pcchip->clk))
  97                 return dev_err_probe(&pdev->dev, PTR_ERR(pcchip->clk),
  98                                      "Failed to get clock\n");
  99
 100         chip->ops = &pwm_clk_ops;
 101
 102         ret = pwmchip_add(chip);
 103         if (ret < 0)
 104                 return dev_err_probe(&pdev->dev, ret, "Failed to add pwm chip\n");
 105
 106         platform_set_drvdata(pdev, chip);
 107         return 0;
 108 }
 109
 110 static void pwm_clk_remove(struct platform_device *pdev)
 111 {
 112         struct pwm_chip *chip = platform_get_drvdata(pdev);
 113         struct pwm_clk_chip *pcchip = to_pwm_clk_chip(chip);
 114
 115         pwmchip_remove(chip);
 116
 117         if (pcchip->clk_enabled)
 118                 clk_disable(pcchip->clk);
 119 }
 120
 121 static const struct of_device_id pwm_clk_dt_ids[] = {
 122         { .compatible = "clk-pwm", },
 123         { /* sentinel */ }
 124 };
 125 MODULE_DEVICE_TABLE(of, pwm_clk_dt_ids);
 126
 127 static struct platform_driver pwm_clk_driver = {
 128         .driver = {
 129                 .name = "pwm-clk",
 130                 .of_match_table = pwm_clk_dt_ids,
 131         },
 132         .probe = pwm_clk_probe,
 133         .remove = pwm_clk_remove,
 134 };
 135 module_platform_driver(pwm_clk_driver);
 136
 137 MODULE_ALIAS("platform:pwm-clk");
 138 MODULE_AUTHOR("Nikita Travkin <nikita@trvn.ru>");
 139 MODULE_DESCRIPTION("Clock based PWM driver");
 140 MODULE_LICENSE("GPL");