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(lài)于自己之外，繼續(xù)看Makefile
obj-$(CONFIG_PWM) += core.oobj-$(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VEVB武林網(wǎng)。
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