linux驱动编写（pwm驱动）

pwm方波可以用来控制很多的设备，比如它可以被用来控制电机。简单来说，就是单位时间内的方波越多，那么电机的转速就会越快；反之就越慢。通过这个特性，soc就可以轻松地利用pwm对外设进行自动控制。所以，今天的主题就是pwm驱动。

1、驱动目录

drivers/pwm

2、查看对应目录下的Kconfig

config PWM_SAMSUNG
  tristate "Samsung PWM support"
  depends on PLAT_SAMSUNG || ARCH_EXYNOS
  help
    Generic PWM framework driver for Samsung.

    To compile this driver as a module, choose M here: the module
    will be called pwm-samsung.

3、确认PWM_SAMSUNG只依赖于自己之外，继续看Makefile

obj-$(CONFIG_PWM)   += core.o

obj-$(CONFIG_PWM_SAMSUNG) += pwm-samsung.o

4、根据Makefile查阅pwm-samsung.c文件，结构比较清楚

static struct platform_driver pwm_samsung_driver = {
  .driver   = {
    .name = "samsung-pwm",
    .pm = &pwm_samsung_pm_ops,
    .of_match_table = of_match_ptr(samsung_pwm_matches),
  },
  .probe    = pwm_samsung_probe,
  .remove   = pwm_samsung_remove,
};
module_platform_driver(pwm_samsung_driver);

5、soc设备大多数是platform设备，继续寻找probe函数中的有用信息

ret = pwmchip_add(&chip->chip);
  if (ret < 0) {
    dev_err(dev, "failed to register PWM chip\n");
    clk_disable_unprepare(chip->base_clk);
    return ret;
  }

6、找到注册函数后，接续看看函数接口点在什么地方

static const struct pwm_ops pwm_samsung_ops = {
  .request  = pwm_samsung_request,
  .free   = pwm_samsung_free,
  .enable   = pwm_samsung_enable,
  .disable  = pwm_samsung_disable,
  .config   = pwm_samsung_config,
  .set_polarity = pwm_samsung_set_polarity,
  .owner    = THIS_MODULE,
};

7、pwm设备没有中断函数，一般是立马生效，除此之外，代码中还是有设备树的内容，可以看看

static const struct of_device_id samsung_pwm_matches[] = {
  { .compatible = "samsung,s3c2410-pwm", .data = &s3c24xx_variant },
  { .compatible = "samsung,s3c6400-pwm", .data = &s3c64xx_variant },
  { .compatible = "samsung,s5p6440-pwm", .data = &s5p64x0_variant },
  { .compatible = "samsung,s5pc100-pwm", .data = &s5pc100_variant },
  { .compatible = "samsung,exynos4210-pwm", .data = &s5p64x0_variant },
  {},
};
MODULE_DEVICE_TABLE(of, samsung_pwm_matches);

static int pwm_samsung_parse_dt(struct samsung_pwm_chip *chip)
{
  struct device_node *np = chip->chip.dev->of_node;
  const struct of_device_id *match;
  struct property *prop;
  const __be32 *cur;
  u32 val;

  match = of_match_node(samsung_pwm_matches, np);
  if (!match)
    return -ENODEV;

  memcpy(&chip->variant, match->data, sizeof(chip->variant));

  of_property_for_each_u32(np, "samsung,pwm-outputs", prop, cur, val) {
    if (val >= SAMSUNG_PWM_NUM) {
      dev_err(chip->chip.dev,
        "%s: invalid channel index in samsung,pwm-outputs property\n",
                __func__);
      continue;
    }
    chip->variant.output_mask |= BIT(val);
  }

  return 0;
}

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linux驱动编写（pwm驱动）

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