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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