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 pwm_chip chip;
  32         struct clk *clk;
  33         bool clk_enabled;
  34 };
  35
  36 #define to_pwm_clk_chip(_chip) container_of(_chip, struct pwm_clk_chip, chip)
  37
  38 static int pwm_clk_apply(struct pwm_chip *chip, struct pwm_device *pwm,
  39                          const struct pwm_state *state)
  40 {
  41         struct pwm_clk_chip *pcchip = to_pwm_clk_chip(chip);
  42         int ret;
  43         u32 rate;
  44         u64 period = state->period;
  45         u64 duty_cycle = state->duty_cycle;
  46
  47         if (!state->enabled) {
  48                 if (pwm->state.enabled) {
  49                         clk_disable(pcchip->clk);
  50                         pcchip->clk_enabled = false;
  51                 }
  52                 return 0;
  53         } else if (!pwm->state.enabled) {
  54                 ret = clk_enable(pcchip->clk);
  55                 if (ret)
  56                         return ret;
  57                 pcchip->clk_enabled = true;
  58         }
  59
  60         /*
  61          * We have to enable the clk before setting the rate and duty_cycle,
  62          * that however results in a window where the clk is on with a
  63          * (potentially) different setting. Also setting period and duty_cycle
  64          * are two separate calls, so that probably isn't atomic either.
  65          */
  66
  67         rate = DIV64_U64_ROUND_UP(NSEC_PER_SEC, period);
  68         ret = clk_set_rate(pcchip->clk, rate);
  69         if (ret)
  70                 return ret;
  71
  72         if (state->polarity == PWM_POLARITY_INVERSED)
  73                 duty_cycle = period - duty_cycle;
  74
  75         return clk_set_duty_cycle(pcchip->clk, duty_cycle, period);
  76 }
  77
  78 static const struct pwm_ops pwm_clk_ops = {
  79         .apply = pwm_clk_apply,
  80         .owner = THIS_MODULE,
  81 };
  82
  83 static int pwm_clk_probe(struct platform_device *pdev)
  84 {
  85         struct pwm_clk_chip *pcchip;
  86         int ret;
  87
  88         pcchip = devm_kzalloc(&pdev->dev, sizeof(*pcchip), GFP_KERNEL);
  89         if (!pcchip)
  90                 return -ENOMEM;
  91
  92         pcchip->clk = devm_clk_get_prepared(&pdev->dev, NULL);
  93         if (IS_ERR(pcchip->clk))
  94                 return dev_err_probe(&pdev->dev, PTR_ERR(pcchip->clk),
  95                                      "Failed to get clock\n");
  96
  97         pcchip->chip.dev = &pdev->dev;
  98         pcchip->chip.ops = &pwm_clk_ops;
  99         pcchip->chip.npwm = 1;
 100
 101         ret = pwmchip_add(&pcchip->chip);
 102         if (ret < 0)
 103                 return dev_err_probe(&pdev->dev, ret, "Failed to add pwm chip\n");
 104
 105         platform_set_drvdata(pdev, pcchip);
 106         return 0;
 107 }
 108
 109 static void pwm_clk_remove(struct platform_device *pdev)
 110 {
 111         struct pwm_clk_chip *pcchip = platform_get_drvdata(pdev);
 112
 113         pwmchip_remove(&pcchip->chip);
 114
 115         if (pcchip->clk_enabled)
 116                 clk_disable(pcchip->clk);
 117 }
 118
 119 static const struct of_device_id pwm_clk_dt_ids[] = {
 120         { .compatible = "clk-pwm", },
 121         { /* sentinel */ }
 122 };
 123 MODULE_DEVICE_TABLE(of, pwm_clk_dt_ids);
 124
 125 static struct platform_driver pwm_clk_driver = {
 126         .driver = {
 127                 .name = "pwm-clk",
 128                 .of_match_table = pwm_clk_dt_ids,
 129         },
 130         .probe = pwm_clk_probe,
 131         .remove_new = pwm_clk_remove,
 132 };
 133 module_platform_driver(pwm_clk_driver);
 134
 135 MODULE_ALIAS("platform:pwm-clk");
 136 MODULE_AUTHOR("Nikita Travkin <nikita@trvn.ru>");
 137 MODULE_DESCRIPTION("Clock based PWM driver");
 138 MODULE_LICENSE("GPL");