linux中pwm驱动编写的示例分析

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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。

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-$(CONFIG_PWM) += core.oobj-$(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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