详解linux pwm驱动编写

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

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1	drivers/pwm

2、查看对应目录下的Kconfig

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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

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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

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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

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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

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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

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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; }

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持服务器之家。

原文链接：https://blog.csdn.net/feixiaoxing/article/details/79889240