开发板：tiny4412SDK + S702 + 4GB Flash
要移植的内核版本：Linux-4.4.0 （支持device tree）
u-boot版本：友善之臂自带的 U-Boot 2010.12
busybox版本：busybox 1.25
目标：
学习设备树中 Clock 的使用，使能 PWM CLOCK 输出 PWM 脉冲，写简单的字符设备驱动程序，使蜂鸣器发出响声。
原理图：
tiny4412 底板上有一颗有源蜂鸣器，有源蜂鸣器的特点是给它一个高电平它就发出响声，无源蜂鸣器才是真正需要脉冲才能发声的。这里仅仅是学习设备树中 clock 资源的使用，使能 PWM 发出间歇性的响声。
设备树：
pwm_demo@139D0000{ compatible = "tiny4412,pwm_demo"; reg = <0x139D0000 0x14>; pinctrl-names = "pwm_pin"; //这里可以设置为pinctrl-names = "default";代码中就免去 devm_pinctrl_get ...等等操作了 pinctrl-0 = <&pwm_pin>; //PWM ADC 等等模块都需要使能时钟模块才能工作,CLK_PWM定义在Exynos4.h (include\dt-bindings\clock) clock-names = "timers";};pwm_pin: pwm_pin{ samsung,pins = "gpd0-0"; samsung,pin-function = <2>; samsung,pin-pud = <0>; samsung,pin-drv = <0>;};
首先，我们需要配置 gpd0_0 引脚为 pwm 输出功能，然后使能 pwm clock，这里多说一句，clock 也是电源管理的一种方式，设备不工作时关闭它的时钟，待其需要工作时再开启。
此外，这里 reg 中指定的是 pwm 相关的寄存器的地址范围，我们在代码中需要设置寄存器，分频系数等等。和平台设备驱动一样，我们可以使用 platform_get_resource(pdev, IORESOURCE_MEM, 0);来获取该类资源。
代码片段：
static int pwm_probe(struct platform_device *pdev) { dev_t devid; struct device *dev = &pdev->dev; struct resource *res = NULL; struct pinctrl *pctrl; struct pinctrl_state *pstate; struct clk *base_clk; int ret; printk("enter %s\n",__func__); pctrl = devm_pinctrl_get(dev); if(pctrl == NULL) { printk("devm_pinctrl_get error\n"); return -EINVAL; } pstate = pinctrl_lookup_state(pctrl, "pwm_pin"); if(pstate == NULL) { printk("pinctrl_lookup_state error\n"); return -EINVAL; } pinctrl_select_state(pctrl, pstate); res = platform_get_resource(pdev, IORESOURCE_MEM, 0); if(res == NULL) { printk("platform_get_resource error\n"); return -EINVAL; } printk("res: %x\n",(unsigned int)res->start); base_clk = devm_clk_get(&pdev->dev, "timers"); if (IS_ERR(base_clk)) { dev_err(dev, "failed to get timer base clk\n"); return PTR_ERR(base_clk); } ret = clk_prepare_enable(base_clk); if (ret < 0) { dev_err(dev, "failed to enable base clock\n"); return ret; } timer = devm_ioremap_resource(&pdev->dev, res); if(timer == NULL) { printk("devm_ioremap_resource error\n"); return -EINVAL; } printk("timer: %x\n",(unsigned int)timer); timer->TCFG0 = (timer->TCFG0 &~(0xff << 0)) | (0xfa << 0); timer->TCFG1 = (timer->TCFG1 &~(0x0f << 0)) | (0x02 << 0); timer->TCNTB0 = 100000; timer->TCMPB0 = 90000; timer->TCON = (timer->TCON &~(0x0f << 0)) | (0x06 << 0); printk("%x %x %x %x %x\n",timer->TCFG0,timer->TCFG1,timer->TCNTB0,timer->TCMPB0,timer->TCON);
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完整代码：
#include <linux/module.h>#include <linux/kernel.h>#include <linux/cdev.h>#include <linux/device.h>#include <linux/platform_device.h>#include <linux/gpio.h>#include <linux/of.h>#include <linux/of_gpio.h>#include <linux/fs.h>#include <asm/uaccess.h>#include <linux/bitops.h>#include <linux/clk.h>#include <linux/export.h>#include <linux/err.h>#include <linux/io.h>#include <linux/pwm.h>#include <linux/slab.h>#include <linux/spinlock.h>#include <linux/time.h>#define MAGIC_NUMBER 'k' #define BEEP_ON _IO(MAGIC_NUMBER ,0) #define BEEP_OFF _IO(MAGIC_NUMBER ,1) #define BEEP_FREQ _IO(MAGIC_NUMBER ,2) static int major;static struct cdev pwm_cdev; static struct class *cls;struct TIMER_BASE{ unsigned int TCFG0; unsigned int TCFG1; unsigned int TCON; unsigned int TCNTB0; unsigned int TCMPB0; };volatile static struct TIMER_BASE * timer = NULL;#define BEPP_IN_FREQ 100000 static void beep_freq(unsigned long arg) { printk("ioctl %d\n",(unsigned int)arg); timer->TCNTB0 = BEPP_IN_FREQ; timer->TCMPB0 = BEPP_IN_FREQ / arg; timer->TCON = (timer->TCON &~(0x0f << 0)) | (0x06 << 0); timer->TCON = (timer->TCON &~(0xff))| 0x0d;} static void beep_on(void){ printk("beep on\n"); timer->TCON = (timer->TCON &~(0xff))| 0x0d; printk("%x\n",timer->TCON);}static void beep_off(void){ timer->TCON = timer->TCON & ~(0x01);}static long pwm_ioctl(struct file *filep, unsigned int cmd, unsigned long arg) { switch(cmd) { case BEEP_ON: beep_on(); break; case BEEP_OFF: beep_off(); break; case BEEP_FREQ: beep_freq(arg); break; default : return -EINVAL; }; return 0;} static int pwm_open(struct inode *inode, struct file *file){ printk("pwm_open\n"); return 0;}static int pwm_release(struct inode *inode, struct file *file){ printk("pwm_exit\n"); return 0;}static struct file_operations pwm_fops = { .owner = THIS_MODULE, .open = pwm_open, .release = pwm_release, .unlocked_ioctl = pwm_ioctl, };static int pwm_probe(struct platform_device *pdev) { dev_t devid; struct device *dev = &pdev->dev; struct resource *res = NULL; struct pinctrl *pctrl; struct pinctrl_state *pstate; struct clk *base_clk; int ret; printk("enter %s\n",__func__); pctrl = devm_pinctrl_get(dev); if(pctrl == NULL) { printk("devm_pinctrl_get error\n"); return -EINVAL; } pstate = pinctrl_lookup_state(pctrl, "pwm_pin"); if(pstate == NULL) { printk("pinctrl_lookup_state error\n"); return -EINVAL; } pinctrl_select_state(pctrl, pstate); res = platform_get_resource(pdev, IORESOURCE_MEM, 0); if(res == NULL) { printk("platform_get_resource error\n"); return -EINVAL; } printk("res: %x\n",(unsigned int)res->start); base_clk = devm_clk_get(&pdev->dev, "timers"); if (IS_ERR(base_clk)) { dev_err(dev, "failed to get timer base clk\n"); return PTR_ERR(base_clk); } ret = clk_prepare_enable(base_clk); if (ret < 0) { dev_err(dev, "failed to enable base clock\n"); return ret; } timer = devm_ioremap_resource(&pdev->dev, res); if(timer == NULL) { printk("devm_ioremap_resource error\n"); return -EINVAL; } printk("timer: %x\n",(unsigned int)timer); timer->TCFG0 = (timer->TCFG0 &~(0xff << 0)) | (0xfa << 0); timer->TCFG1 = (timer->TCFG1 &~(0x0f << 0)) | (0x02 << 0); timer->TCNTB0 = 100000; timer->TCMPB0 = 90000; timer->TCON = (timer->TCON &~(0x0f << 0)) | (0x06 << 0); printk("%x %x %x %x %x\n",timer->TCFG0,timer->TCFG1,timer->TCNTB0,timer->TCMPB0,timer->TCON); if(alloc_chrdev_region(&devid, 0, 1, "pwm") < 0) { printk("%s ERROR\n",__func__); goto error; } major = MAJOR(devid); cdev_init(&pwm_cdev, &pwm_fops); cdev_add(&pwm_cdev, devid, 1); cls = class_create(THIS_MODULE, "mypwm"); device_create(cls, NULL, MKDEV(major, 0), NULL, "pwm0"); error: unregister_chrdev_region(MKDEV(major, 0), 1); return 0;}static int pwm_remove(struct platform_device *pdev){ printk("enter %s\n",__func__); device_destroy(cls, MKDEV(major, 0)); class_destroy(cls); cdev_del(&pwm_cdev); unregister_chrdev_region(MKDEV(major, 0), 1); printk("%s enter.\n", __func__); return 0;}static const struct of_device_id pwm_dt_ids[] = { { .compatible = "tiny4412,pwm_demo", }, {},};MODULE_DEVICE_TABLE(of, pwm_dt_ids);static struct platform_driver pwm_driver = { .driver = { .name = "pwm_demo", .of_match_table = of_match_ptr(pwm_dt_ids), }, .probe = pwm_probe, .remove = pwm_remove,};static int pwm_init(void){ int ret; printk("enter %s\n",__func__); ret = platform_driver_register(&pwm_driver); if (ret) printk(KERN_ERR "pwm demo: probe faipwm: %d\n", ret); return ret; }static void pwm_exit(void){ printk("enter %s\n",__func__); platform_driver_unregister(&pwm_driver);}module_init(pwm_init);module_exit(pwm_exit);MODULE_LICENSE("GPL");
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