关于mini2440触摸屏驱动中信号量作用的最新解释

这几天仔细分析了下触摸屏驱动程序，对触摸屏驱动程序stylus_action函数中的mod_timer()不是很理解，于是在触摸屏驱动程序中加上了debug信息，进行了测试。添加debug信息后的去驱动代码如下：

/*************************************NAME:gt2440.cCOPYRIGHT:www.e-online.cc*************************************/#include <linux/errno.h>#include <linux/kernel.h>#include <linux/module.h>#include <linux/slab.h>#include <linux/input.h>#include <linux/init.h>#include <linux/serio.h>#include <linux/delay.h>#include <linux/platform_device.h>#include <linux/clk.h>#include <asm/io.h>#include <asm/irq.h>#include <plat/regs-adc.h>#include <mach/regs-gpio.h>/* For ts.dev.id.version */#define TSDEBUG#ifdef TSDEBUG#define TPDEBUG(fmt,args...) printk("gt2440 ts:" fmt,##args)#else#define TPDEBUG(fmt,args...)#endif#define S3C2410TSVERSION0x0101#define WAIT4INT(x)  (((x)<<8) | \     S3C2410_ADCTSC_YM_SEN | S3C2410_ADCTSC_YP_SEN | S3C2410_ADCTSC_XP_SEN | \     S3C2410_ADCTSC_XY_PST(3))#define AUTOPST     (S3C2410_ADCTSC_YM_SEN | S3C2410_ADCTSC_YP_SEN | S3C2410_ADCTSC_XP_SEN | \     S3C2410_ADCTSC_AUTO_PST | S3C2410_ADCTSC_XY_PST(0))static char *gt2440ts_name = "GT2440 TouchScreen";staticstruct input_dev *dev;staticlong xp;staticlong yp;staticint count;extern struct semaphore ADC_LOCK;static int OwnADC = 0;static void __iomem *base_addr;static inline void gt2440_ts_connect(void){s3c2410_gpio_cfgpin(S3C2410_GPG12, S3C2410_GPG12_XMON);s3c2410_gpio_cfgpin(S3C2410_GPG13, S3C2410_GPG13_nXPON);s3c2410_gpio_cfgpin(S3C2410_GPG14, S3C2410_GPG14_YMON);s3c2410_gpio_cfgpin(S3C2410_GPG15, S3C2410_GPG15_nYPON);}static void touch_timer_fire(unsigned long data){  unsigned long data0;  unsigned long data1;int updown;  data0 = ioread32(base_addr+S3C2410_ADCDAT0);  data1 = ioread32(base_addr+S3C2410_ADCDAT1); updown = (!(data0 & S3C2410_ADCDAT0_UPDOWN)) && (!(data1 & S3C2410_ADCDAT0_UPDOWN)); if (updown) { if (count != 0) {                        xp >>= 2;                        yp >>= 2; input_report_abs(dev, ABS_X, xp); input_report_abs(dev, ABS_Y, yp); input_report_key(dev, BTN_TOUCH, 1); input_report_abs(dev, ABS_PRESSURE, 1); input_sync(dev);TPDEBUG("touch_timer_fire func report key:%d,%d\n",xp,yp); } xp = 0; yp = 0; count = 0; iowrite32(S3C2410_ADCTSC_PULL_UP_DISABLE | AUTOPST, base_addr+S3C2410_ADCTSC); iowrite32(ioread32(base_addr+S3C2410_ADCCON) | S3C2410_ADCCON_ENABLE_START, base_addr+S3C2410_ADCCON);TPDEBUG("touch_timer_fire func start ADC\n"); } else { count = 0; input_report_key(dev, BTN_TOUCH, 0); input_report_abs(dev, ABS_PRESSURE, 0); input_sync(dev); iowrite32(WAIT4INT(0), base_addr+S3C2410_ADCTSC);if (OwnADC){OwnADC = 0;up(&ADC_LOCK);}TPDEBUG("touch_timer_fire func stylus up\n"); }}static struct timer_list touch_timer =TIMER_INITIALIZER(touch_timer_fire, 0, 0);static irqreturn_t stylus_updown(int irq, void *dev_id){unsigned long data0;unsigned long data1;int updown;TPDEBUG("stylus_updown func init\n");if (down_trylock(&ADC_LOCK) == 0){OwnADC = 1;data0 = ioread32(base_addr+S3C2410_ADCDAT0);data1 = ioread32(base_addr+S3C2410_ADCDAT1);updown = (!(data0 & S3C2410_ADCDAT0_UPDOWN)) && (!(data1 & S3C2410_ADCDAT0_UPDOWN));if (updown){TPDEBUG("stylus_updown func:stylus down\n");touch_timer_fire(0);}else{TPDEBUG("stylus_updown func:stylus up\n");OwnADC = 0;up(&ADC_LOCK);}}return IRQ_HANDLED;}static irqreturn_t stylus_action(int irq, void *dev_id){unsigned long data0;unsigned long data1;if (OwnADC){data0 = ioread32(base_addr+S3C2410_ADCDAT0);data1 = ioread32(base_addr+S3C2410_ADCDAT1);xp += data0 & S3C2410_ADCDAT0_XPDATA_MASK;yp += data1 & S3C2410_ADCDAT1_YPDATA_MASK;count++;if (count < (1<<4)){iowrite32(S3C2410_ADCTSC_PULL_UP_DISABLE | AUTOPST, base_addr+S3C2410_ADCTSC);iowrite32(ioread32(base_addr+S3C2410_ADCCON) | S3C2410_ADCCON_ENABLE_START, base_addr+S3C2410_ADCCON);TPDEBUG("stylus_action func still adc\n");}else{TPDEBUG("stylus_action func report key\n");mod_timer(&touch_timer, jiffies+1);iowrite32(WAIT4INT(1), base_addr+S3C2410_ADCTSC);TPDEBUG("stylus_action func wait interrupt\n");}}return IRQ_HANDLED;}static struct clk*adc_clock;static int __init gt2440ts_init(void){struct input_dev *input_dev;adc_clock = clk_get(NULL, "adc");if (!adc_clock){printk(KERN_ERR "failed to get adc clock source\n");return -ENOENT;}clk_enable(adc_clock);base_addr=ioremap(S3C2410_PA_ADC,0x20);if (base_addr == NULL){printk(KERN_ERR "Failed to remap register block\n");return -ENOMEM;}/* Configure GPIOs *///gt2440_ts_connect();iowrite32(S3C2410_ADCCON_PRSCEN | S3C2410_ADCCON_PRSCVL(100),base_addr+S3C2410_ADCCON);iowrite32(0x4fff, base_addr+S3C2410_ADCDLY);iowrite32(WAIT4INT(0), base_addr+S3C2410_ADCTSC);/* Initialise input stuff */input_dev = input_allocate_device();if (!input_dev){printk(KERN_ERR "Unable to allocate the input device !!\n");return -ENOMEM;}dev = input_dev;dev->evbit[0] = BIT(EV_SYN) | BIT(EV_KEY) | BIT(EV_ABS);dev->keybit[BITS_TO_LONGS(BTN_TOUCH)] = BIT(BTN_TOUCH);input_set_abs_params(dev, ABS_X, 0, 0x3FF, 0, 0);input_set_abs_params(dev, ABS_Y, 0, 0x3FF, 0, 0);input_set_abs_params(dev, ABS_PRESSURE, 0, 1, 0, 0);dev->name = gt2440ts_name;dev->id.bustype = BUS_RS232;dev->id.vendor = 0xDEAD;dev->id.product = 0xBEEF;dev->id.version = S3C2410TSVERSION;if (request_irq(IRQ_ADC, stylus_action, IRQF_SHARED|IRQF_SAMPLE_RANDOM, gt2440ts_name, dev)){printk(KERN_ERR "gt2440_ts.c: Could not allocate ts IRQ_ADC !\n");iounmap(base_addr);return -EIO;}if (request_irq(IRQ_TC, stylus_updown, IRQF_SAMPLE_RANDOM, gt2440ts_name, dev)){printk(KERN_ERR "gt2440_ts.c: Could not allocate ts IRQ_ADC !\n");iounmap(base_addr);return -EIO;}printk(KERN_INFO "%s successfully loaded\n", gt2440ts_name);input_register_device(dev);return 0;}static void __exit gt2440ts_exit(void){disable_irq(IRQ_ADC);disable_irq(IRQ_TC);free_irq(IRQ_TC,dev);free_irq(IRQ_ADC,dev);if (adc_clock){clk_disable(adc_clock);clk_put(adc_clock);adc_clock = NULL;}input_unregister_device(dev);iounmap(base_addr);}module_init(gt2440ts_init);module_exit(gt2440ts_exit);

驱动程序测试结果输入：

gt2440 ts: stylus_updown func initgt2440 ts: stylus_updown func:stylus downgt2440 ts: touch_timer_fire func start ADCgt2440 ts: stylus_action func still adcgt2440 ts: stylus_action func still adcgt2440 ts: stylus_action func still adcgt2440 ts: stylus_action func still adcgt2440 ts: stylus_action func still adcgt2440 ts: stylus_action func still adcgt2440 ts: stylus_action func still adcgt2440 ts: stylus_action func still adcgt2440 ts: stylus_action func still adcgt2440 ts: stylus_action func still adcgt2440 ts: stylus_action func still adcgt2440 ts: stylus_action func still adcgt2440 ts: stylus_action func still adcgt2440 ts: stylus_action func still adcgt2440 ts: stylus_action func still adcgt2440 ts: stylus_action func report keygt2440 ts: stylus_action func wait interruptgt2440 ts: stylus_updown func inigt2440 ts: touch_timer_fire func report key 676,,4347 

根据后面的三条输出结果我们在分析一遍程序stylus_updown()->touch_timer_fire()->stylus_action()->stylus_updown()->touch_timer_fire(),因此，stylus_updown函数中的if (down_trylock(&ADC_LOCK) == 0)不仅仅是保证任何时候都只有一个驱动程序使用ADC，同时还有一个重要作用就是保证当触摸屏一直被按下时，不重复进入终端触发定时器函数。