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詳解linux pwm驅(qū)動(dòng)編寫(xiě)

更新時(shí)間：2018年04月11日 09:33:05 作者：feixiaoxing

這篇文章主要介紹了詳解linux pwm驅(qū)動(dòng)編寫(xiě)，小編覺(jué)得挺不錯(cuò)的，現(xiàn)在分享給大家，也給大家做個(gè)參考。一起跟隨小編過(guò)來(lái)看看吧

pwm方波可以用來(lái)控制很多的設(shè)備，比如它可以被用來(lái)控制電機(jī)。簡(jiǎn)單來(lái)說(shuō)，就是單位時(shí)間內(nèi)的方波越多，那么電機(jī)的轉(zhuǎn)速就會(huì)越快；反之就越慢。通過(guò)這個(gè)特性，soc就可以輕松地利用pwm對(duì)外設(shè)進(jìn)行自動(dòng)控制。所以，今天的主題就是pwm驅(qū)動(dòng)。

1、驅(qū)動(dòng)目錄

drivers/pwm

2、查看對(duì)應(yīng)目錄下的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、確認(rèn)PWM_SAMSUNG只依賴于自己之外，繼續(xù)看Makefile

obj-$(CONFIG_PWM) += core.o

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

4、根據(jù)Makefile查閱pwm-samsung.c文件，結(jié)構(gòu)比較清楚

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設(shè)備大多數(shù)是platform設(shè)備，繼續(xù)尋找probe函數(shù)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、找到注冊(cè)函數(shù)后，接續(xù)看看函數(shù)接口點(diǎn)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設(shè)備沒(méi)有中斷函數(shù)，一般是立馬生效，除此之外，代碼中還是有設(shè)備樹(shù)的內(nèi)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;
}

以上就是本文的全部?jī)?nèi)容，希望對(duì)大家的學(xué)習(xí)有所幫助，也希望大家多多支持腳本之家。

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