col作为输出，row作为输入检测，低电平有效
col A~D轮流输出低电平，通过rol 1~4上的低电平可以检测是哪个按键按下了但是存在这样的问题，A1，A2，B1同时按下，会造成B2按下的假象，称为鬼影（这3个键导通，colB打开，row2处也会检测到低电平）

可以通过增加二极管的方式防止鬼影问题

keypad@10010000 {compatible = "mediatek,mt6755-keypad", "mediatek,kp";reg = <0x10010000 0x1000>;interrupts = <0x0 0xa4 0x2>;mediatek,kpd-key-debounce = <0x400>;mediatek,kpd-sw-pwrkey = <0x74>;mediatek,kpd-hw-pwrkey = <0x8>;mediatek,kpd-sw-rstkey = <0x73>;mediatek,kpd-hw-rstkey = <0x11>;mediatek,kpd-use-extend-type = <0x0>;mediatek,kpd-hw-map-num = <0x48>;mediatek,kpd-hw-init-map = <0x72 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0>;mediatek,kpd-pwrkey-eint-gpio = <0x0>;mediatek,kpd-pwkey-gpio-din = <0x0>;mediatek,kpd-hw-dl-key0 = <0x11>;mediatek,kpd-hw-dl-key1 = <0x0>;mediatek,kpd-hw-dl-key2 = <0x8>;mediatek,kpd-hw-recovery-key = <0x11>;mediatek,kpd-hw-factory-key = <0x0>;status = "okay";};

static int kpd_pdrv_probe(struct platform_device *pdev)
{int i, r;int err = 0;struct clk *kpd_clk = NULL;
//获取clk，这里kpd-clk是通过ccf设置的kpd_clk = devm_clk_get(&pdev->dev, "kpd-clk");if (!IS_ERR(kpd_clk)) {int ret_prepare, ret_enable;ret_prepare = clk_prepare(kpd_clk);if (ret_prepare)kpd_print("clk_prepare returned %d\n", ret_prepare);ret_enable = clk_enable(kpd_clk);if (ret_enable)kpd_print("clk_enable returned %d\n", ret_prepare);} else {kpd_print("get kpd-clk fail, but not return, maybe kpd-clk is set by ccf.\n");}
//reg重映射kp_base = of_iomap(pdev->dev.of_node, 0);if (!kp_base) {kpd_info("KP iomap failed\n");return -ENODEV;};
//irq映射kp_irqnr = irq_of_parse_and_map(pdev->dev.of_node, 0);if (!kp_irqnr) {kpd_info("KP get irqnr failed\n");return -ENODEV;}
//申请input设备kpd_input_dev = input_allocate_device();if (!kpd_input_dev) {kpd_print("input allocate device fail.\n");return -ENOMEM;}
//input设备初始化kpd_input_dev->name = KPD_NAME;kpd_input_dev->id.bustype = BUS_HOST;kpd_input_dev->id.vendor = 0x2454;kpd_input_dev->id.product = 0x6500;kpd_input_dev->id.version = 0x0010;kpd_input_dev->open = kpd_open;
//解析dts中keypad节点的信息，赋值给kpd_dts_data结构体kpd_get_dts_info(pdev->dev.of_node);
//分配内存空间，用于存放键值和按键状态寄存器kpd_memory_setting();
//input设备支持EV_KEY事件__set_bit(EV_KEY, kpd_input_dev->evbit);
//powerkey连接PMIC，kpd_keymap[8]设置为空
#if defined(CONFIG_KPD_PWRKEY_USE_EINT) || defined(CONFIG_KPD_PWRKEY_USE_PMIC)__set_bit(kpd_dts_data.kpd_sw_pwrkey, kpd_input_dev->keybit);kpd_keymap[8] = 0;
#endif//powerkey列除[8]外，其余都清空    if (!kpd_dts_data.kpd_use_extend_type) {for (i = 17; i < KPD_NUM_KEYS; i += 9)    /* only [8] works for Power key */kpd_keymap[i] = 0;}//设置设备支持的键值for (i = 0; i < KPD_NUM_KEYS; i++) {if (kpd_keymap[i] != 0)__set_bit(kpd_keymap[i], kpd_input_dev->keybit);}
//reset按键if (kpd_dts_data.kpd_sw_rstkey)__set_bit(kpd_dts_data.kpd_sw_rstkey, kpd_input_dev->keybit);
kpd_input_dev->dev.parent = &pdev->dev;//注册input设备r = input_register_device(kpd_input_dev);if (r) {kpd_info("register input device failed (%d)\n", r);input_free_device(kpd_input_dev);return r;}/* register device (/dev/mt6575-kpd) */kpd_dev.parent = &pdev->dev;r = misc_register(&kpd_dev);if (r) {kpd_info("register device failed (%d)\n", r);input_unregister_device(kpd_input_dev);return r;}
//初始化wake_lockwake_lock_init(&kpd_suspend_lock, WAKE_LOCK_SUSPEND, "kpd wakelock");//设置按键消抖并申请中断处理kpd_set_debounce(kpd_dts_data.kpd_key_debounce);r = request_irq(kp_irqnr, kpd_irq_handler, IRQF_TRIGGER_NONE, KPD_NAME, NULL);if (r) {kpd_info("register IRQ failed (%d)\n", r);misc_deregister(&kpd_dev);input_unregister_device(kpd_input_dev);return r;}

#ifndef KPD_EARLY_PORTING    /*add for avoid early porting build err the macro is defined in custom file */long_press_reboot_function_setting();    /* /API 4 for kpd long press reboot function setting */
#endifhrtimer_init(&aee_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);aee_timer.function = aee_timer_func;
//添加文件属性err = kpd_create_attr(&kpd_pdrv.driver);if (err) {kpd_info("create attr file fail\n");kpd_delete_attr(&kpd_pdrv.driver);return err;}kpd_info("%s Done\n", __func__);return 0;
}

static irqreturn_t kpd_irq_handler(int irq, void *dev_id)
{
//禁止中断，无需进行同步，防止死锁disable_irq_nosync(kp_irqnr);//调度tasklettasklet_schedule(&kpd_keymap_tasklet);return IRQ_HANDLED;
}

//定义tasklet，执行kpd_keymap_handler函数static DECLARE_TASKLET(kpd_keymap_tasklet, kpd_keymap_handler, 0);

static void kpd_keymap_handler(unsigned long data)
{int i, j;bool pressed;u16 new_state[KPD_NUM_MEMS], change, mask;u16 hw_keycode, linux_keycode;
//mtk通过5组寄存器来保存按键的状态，这里回读寄存器并保存为new_statekpd_get_keymap_state(new_state);
//激活锁唤醒系统，500ms后就释放掉wake_lock_timeout(&kpd_suspend_lock, HZ / 2);for (i = 0; i < KPD_NUM_MEMS; i++) {//每组中按键状态未改变则对比下一组，按位处理change = new_state[i] ^ kpd_keymap_state[i];if (!change)continue;for (j = 0; j < 16; j++) {//每组（16位）中对比按位查看是否状态发生改变mask = 1U << j;if (!(change & mask))continue;hw_keycode = (i << 4) + j;/* bit is 1: not pressed, 0: pressed */
//按键是否按下，寄存器中0表示按键处于按下状态                        pressed = !(new_state[i] & mask);if (kpd_show_hw_keycode)kpd_print("(%s) HW keycode = %u\n", pressed ? "pressed" : "released", hw_keycode);BUG_ON(hw_keycode >= KPD_NUM_KEYS);linux_keycode = kpd_keymap[hw_keycode];if (unlikely(linux_keycode == 0)) {kpd_print("Linux keycode = 0\n");continue;}kpd_aee_handler(linux_keycode, pressed);
//上报键值input_report_key(kpd_input_dev, linux_keycode, pressed);input_sync(kpd_input_dev);kpd_print("report Linux keycode = %u\n", linux_keycode);}}
//kpd_keymap_state保存new_state，用于下轮对比memcpy(kpd_keymap_state, new_state, sizeof(new_state));kpd_print("save new keymap state\n");//按键处理完毕，打开中断enable_irq(kp_irqnr);
}