设备树学习之（三）Clock

本文主要是介绍设备树学习之（三）Clock，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

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>;
};
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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;}//设置引脚功能    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>/*PWM 时钟频率 100M100M / 250 / 4 = 1000001/100000 = 10us
*/#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;}//设置引脚功能    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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