詳解linux pwm驅(qū)動(dòng)編寫
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;
}
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