Android Input系统添加自定义键值上报实现(from Linux to Android)

系统环境

博主已在Android 7.0上验证成功，其他后6.0，8.0，9.0应该改动不大，可以直接拿过来使用，底层基本不变，上层Android可能会有些接口调整，不过万变不离其中，也是可以参考的。

Demo原理

博主实现的Demo主要是通过外部串口来发送音量调整数据，给到Android，Android端的serial_comm进程会不断处理串口接收到的信息，然后再通过驱动进行InputEvent上报，触发PhoneWindowManager对上报的自定义按键进行处理，从而调整音量数据。这样处理通过InputEvent上报处理比较及时迅速。

Android系统层

Android上层需要修改这些文件，我直接diff出来了，其中我们新增的键值要注意不要跟系统的重复：KEYCODE_SPECIFIC_VOLUME = 280

diff --git a/android/frameworks/base/core/java/android/view/KeyEvent.java b/android/frameworks/base/core/java/android/view/KeyEvent.java
index b003f00..fabce16 100755
--- a/android/frameworks/base/core/java/android/view/KeyEvent.java
+++ b/android/frameworks/base/core/java/android/view/KeyEvent.java
@@ -809,6 +809,9 @@ public class KeyEvent extends InputEvent implements Parcelable {
     public static final int KEYCODE_COPY = 278;
     /** Key code constant: Paste key. */
     public static final int KEYCODE_PASTE = 279;
+
+    public static final int KEYCODE_SPECIFIC_VOLUME = 280;
+
     /** Key code constant: a shortcut key for mouse */
     public static final int KEYCODE_MOUSE           = 10009;
     public static final int KEYCODE_TV_SYSTEM       = 10000;
diff --git a/android/frameworks/base/core/res/res/values/attrs.xml b/android/frameworks/base/core/res/res/values/attrs.xml
index b61d6cf..4330802 100644
--- a/android/frameworks/base/core/res/res/values/attrs.xml
+++ b/android/frameworks/base/core/res/res/values/attrs.xml
@@ -1832,6 +1832,7 @@ i
         <enum name="KEYCODE_CUT" value="277" />
         <enum name="KEYCODE_COPY" value="278" />
         <enum name="KEYCODE_PASTE" value="279" />
+        <enum name="KEYCODE_SPECIFIC_VOLUME" value="280" />
     </attr>
 
     <!-- ***************************************************************** -->
diff --git a/android/frameworks/native/include/android/keycodes.h b/android/frameworks/native/include/android/keycodes.h
index 4687b85..9fd76d5 100755
--- a/android/frameworks/native/include/android/keycodes.h
+++ b/android/frameworks/native/include/android/keycodes.h
@@ -758,6 +758,9 @@ enum {
     AKEYCODE_COPY = 278,
     /** Paste key. */
     AKEYCODE_PASTE = 279,
+
+    AKEYCODE_SPECIFIC_VOLUME = 280,
+
     // add for karaok by linjunqian
     AKEYCODE_MIC_VOLUME_UP   = 370,
     AKEYCODE_MIC_VOLUME_DOWN = 371,
diff --git a/android/frameworks/native/include/input/InputEventLabels.h b/android/frameworks/native/include/input/InputEventLabels.h
index 911c568..78ed509 100755
--- a/android/frameworks/native/include/input/InputEventLabels.h
+++ b/android/frameworks/native/include/input/InputEventLabels.h
@@ -319,6 +319,7 @@ static const InputEventLabel KEYCODES[] = {
     DEFINE_KEYCODE(CUT),
     DEFINE_KEYCODE(COPY),
     DEFINE_KEYCODE(PASTE),
+    DEFINE_KEYCODE(SPECIFIC_VOLUME),
     DEFINE_KEYCODE(MIC_VOLUME_UP),
     DEFINE_KEYCODE(MIC_VOLUME_DOWN),
     DEFINE_KEYCODE(KOUT_VOLUME_UP),
diff --git a/android/frameworks/base/services/core/java/com/android/server/policy/PhoneWindowManager.java b/android/frameworks/base/services/core/java/com/android/server/policy/PhoneWindowManager.java
index a4408fc..fbcd7e0 100644
--- a/android/frameworks/base/services/core/java/com/android/server/policy/PhoneWindowManager.java
+++ b/android/frameworks/base/services/core/java/com/android/server/policy/PhoneWindowManager.java
@@ -5530,6 +5530,20 @@ public class PhoneWindowManager implements WindowManagerPolicy {
                 break;
             }
 
+            case KeyEvent.KEYCODE_SPECIFIC_VOLUME: {
+                if (down) {
+                    Log.d(TAG, "KeyEvent.KEYCODE_SPECIFIC_VOLUME down");
+                    AudioManager audioManager = (AudioManager) mContext.getSystemService(Context.AUDIO_SERVICE);
+                    audioManager.setStreamVolume(AudioManager.STREAM_MUSIC,
+                            Integer.parseInt(SystemProperties.get("persist.sys.specific_volume")),
+                            AudioManager.FLAG_SHOW_UI);
+                    Log.d(TAG, "setStreamVolume " + SystemProperties.get("persist.sys.specific_volume"));
+                } else {
+                    Log.d(TAG, "KeyEvent.KEYCODE_SPECIFIC_VOLUME up");
+                }
+                break;
+            }
+
             case KeyEvent.KEYCODE_VOLUME_DOWN:
             case KeyEvent.KEYCODE_VOLUME_UP:
             case KeyEvent.KEYCODE_VOLUME_MUTE: {

到这里我们已经把上层的键值配好了，可以make systemimage -j8，烧进去进行测试，利用input keyevent 280，看看修改是否成功。

中间转换（Android - Linux）

Android自己定义了一套键值，Linux上报的键值需要通过kl文件转换才能正常识别。

diff --git a/android/frameworks/base/data/keyboards/Generic.kl b/android/frameworks/base/data/keyboards/Generic.kl
index 2a10bdd..ed9e1bd 100644
--- a/android/frameworks/base/data/keyboards/Generic.kl
+++ b/android/frameworks/base/data/keyboards/Generic.kl
@@ -247,6 +247,8 @@ key 224   BRIGHTNESS_DOWN
 key 225   BRIGHTNESS_UP
 key 226   HEADSETHOOK
 
+key 249   SPECIFIC_VOLUME
+
 key 256   BUTTON_1
 key 257   BUTTON_2
 key 258   BUTTON_3

Linux底层

从下面可以看到，我们再Linux层定义的键值为#define KEY_SPECIFIC_VOLUME 249，这里我写了个虚拟按键的驱动程序，echo 1 > /sys/kernel/virtual_key，在往virtual_key节点写1的时候就会上报KEY_SPECIFIC_VOLUME键，从而通知Android上层进行处理。

diff --git a/lichee/linux-3.10/include/uapi/linux/input.h b/lichee/linux-3.10/include/uapi/linux/input.h
index 74b5a00..5413c97 100644
--- a/lichee/linux-3.10/include/uapi/linux/input.h
+++ b/lichee/linux-3.10/include/uapi/linux/input.h
@@ -473,6 +473,8 @@ struct input_keymap_entry {
 
 #define KEY_MICMUTE        248    /* Mute / unmute the microphone */
 
+#define KEY_SPECIFIC_VOLUME    249
+
 #define KEY_VOICE_ASSIST 582
 /* Code 255 is reserved for special needs of AT keyboard driver */
diff --git a/lichee/linux-3.10/arch/arm64/configs/sun50iw6p1smp_android_7.x_defconfig b/lichee/linux-3.10/arch/arm64/configs/sun50iw6p1smp_android_7.x_defconfig
index 6d0ccaa..cc15e9a 100644
--- a/lichee/linux-3.10/arch/arm64/configs/sun50iw6p1smp_android_7.x_defconfig
+++ b/lichee/linux-3.10/arch/arm64/configs/sun50iw6p1smp_android_7.x_defconfig
@@ -1287,6 +1287,7 @@ CONFIG_INPUT_EVDEV=y
 CONFIG_INPUT_KEYRESET=y
 CONFIG_INPUT_KEYCOMBO=y
 # CONFIG_INPUT_POWERKEY is not set
+CONFIG_INPUT_VIRTUALKEY=y
 CONFIG_INPUT_SW_DEVICE=m
 
 #
diff --git a/lichee/linux-3.10/drivers/input/Kconfig b/lichee/linux-3.10/drivers/input/Kconfig
index 77a12a9..9c6f668 100755
--- a/lichee/linux-3.10/drivers/input/Kconfig
+++ b/lichee/linux-3.10/drivers/input/Kconfig
@@ -205,6 +205,16 @@ config INPUT_POWERKEY
       To compile this driver as a module,choose M here: the
       module will be called sunxi-gpiokey.
 
+config INPUT_VIRTUALKEY
+        tristate "virtual key"
+        depends on INPUT
+        default n
+        ---help---
+          Say Y here if you want to support go virtual_key;
+
+          To compile this driver as a module,choose M here: the
+          module will be called virtual-key.
+
 config  INPUT_SW_DEVICE
        tristate  "i2c device detect support"
        depends on INPUT && I2C
diff --git a/lichee/linux-3.10/drivers/input/Makefile b/lichee/linux-3.10/drivers/input/Makefile
index a7203f0..a66231a 100755
--- a/lichee/linux-3.10/drivers/input/Makefile
+++ b/lichee/linux-3.10/drivers/input/Makefile
@@ -18,6 +18,8 @@ obj-$(CONFIG_INPUT_EVDEV)    += evdev.o
 obj-$(CONFIG_INPUT_EVBUG)    += evbug.o
 
 obj-$(CONFIG_INPUT_POWERKEY)    += sunxi-gpiokey.o
+obj-$(CONFIG_INPUT_VIRTUALKEY)  += virtual-key.o
+obj-$(CONFIG_INPUT_VIRTUALKEY)  += virtual-key-dev.o
 
 obj-$(CONFIG_INPUT_KEYBOARD)    += keyboard/
 obj-$(CONFIG_INPUT_MOUSE)    += mouse/
diff --git a/lichee/linux-3.10/drivers/input/virtual-key-dev.c b/lichee/linux-3.10/drivers/input/virtual-key-dev.c
new file mode 100644
index 0000000..60c8038
--- /dev/null
+++ b/lichee/linux-3.10/drivers/input/virtual-key-dev.c
@@ -0,0 +1,34 @@
+#include 
+#include 
+#include 
+#include 
+
+static struct platform_device virtual_key_dev = {
+    .name = "virtual_key",
+    .id = -1,
+};
+
+static int __init virtual_key_dev_init(void)
+{
+    printk("%s-%d: enter\n", __FUNCTION__, __LINE__);
+    if (platform_device_register(&virtual_key_dev)) {
+        pr_err("virtual_key virtual_key_dev_init  fail\n");
+        return -1;
+    }
+
+    return 0;
+}
+
+static void __exit virtual_key_dev_exit(void)
+{
+    platform_device_unregister(&virtual_key_dev);
+}
+
+module_init(virtual_key_dev_init);
+module_exit(virtual_key_dev_exit);
+
+MODULE_AUTHOR("sweetmilkcake ");
+MODULE_DESCRIPTION("virtual key dev");
+MODULE_LICENSE("GPL");
+
+
diff --git a/lichee/linux-3.10/drivers/input/virtual-key.c b/lichee/linux-3.10/drivers/input/virtual-key.c
new file mode 100644
index 0000000..0b951d2
--- /dev/null
+++ b/lichee/linux-3.10/drivers/input/virtual-key.c
@@ -0,0 +1,151 @@
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+
+static volatile u32 virtual_key_trigger;
+static struct mutex virtual_key_mutex;
+static struct input_dev *virtual_key_dev;
+
+static ssize_t virtual_key_show(struct kobject *kobj,
+                struct kobj_attribute *attr,
+                char *buf)
+{
+    return sprintf(buf, "%d\n", virtual_key_trigger);
+}
+
+static ssize_t virtual_key_store(struct kobject *kobj,
+                struct kobj_attribute *attr,
+                const char *buf, size_t count)
+{
+    int ret = 0;
+
+    mutex_lock(&virtual_key_mutex);
+
+    switch (buf[0]) {
+    case '0':
+        virtual_key_trigger = 0;
+        break;
+    case '1':
+        virtual_key_trigger = 1;
+        input_report_key(virtual_key_dev, KEY_SPECIFIC_VOLUME, 1);
+        input_sync(virtual_key_dev);
+        input_report_key(virtual_key_dev, KEY_SPECIFIC_VOLUME, 0);
+        input_sync(virtual_key_dev);
+        break;
+    default:
+        ret = -EINVAL;
+        break;
+    }
+
+    mutex_unlock(&virtual_key_mutex);
+    return ret < 0 ? ret : count;
+}
+
+static struct kobj_attribute virtual_key_attr = __ATTR(virtual_key,
+                        0666, virtual_key_show,
+                        virtual_key_store);
+
+static int  virtual_key_probe(struct platform_device *pdev)
+{
+    int err = 0;
+
+    printk("%s-%d: enter\n", __FUNCTION__, __LINE__);
+
+    virtual_key_dev = input_allocate_device();
+    if (!virtual_key_dev) {
+        pr_err("virtual_key: not enough memory for input device\n");
+        err = -ENOMEM;
+        goto fail1;
+    }
+
+    virtual_key_dev->name = "virtual_key";
+    //virtual_key_dev->phys = "sunxikbd/input0";
+    virtual_key_dev->id.bustype = BUS_HOST;
+    virtual_key_dev->id.vendor = 0x0001;
+    virtual_key_dev->id.product = 0x0001;
+    virtual_key_dev->id.version = 0x0100;
+
+#ifdef REPORT_REPEAT_KEY_BY_INPUT_CORE
+    virtual_key_dev->evbit[0] = BIT_MASK(EV_KEY)|BIT_MASK(EV_REP);
+    printk(KERN_DEBUG "REPORT_REPEAT_KEY_BY_INPUT_CORE is defined, support report repeat key value. \n");
+#else
+    virtual_key_dev->evbit[0] = BIT_MASK(EV_KEY);
+#endif
+    set_bit(KEY_SPECIFIC_VOLUME, virtual_key_dev->keybit);
+    mutex_init(&virtual_key_mutex);
+
+    err = input_register_device(virtual_key_dev);
+    if (err)
+        goto fail2;
+
+    err = sysfs_create_file(kernel_kobj, &virtual_key_attr.attr);
+    if (err) {
+        printk(KERN_ERR "virtual_key: unable to create sysfs file"
+            " virtual_key (%d)\n", err);
+        goto fail3;
+    }
+
+    return 0;
+
+fail3:
+    input_unregister_device(virtual_key_dev);
+fail2:
+    input_free_device(virtual_key_dev);
+fail1:
+    printk(KERN_DEBUG "virtual_key_init failed. \n");
+
+    return err;
+}
+
+static int virtual_key_remove(struct platform_device *dev)
+{
+
+    input_unregister_device(virtual_key_dev);
+
+    return 0;
+}
+
+static struct platform_driver virtual_key_driver = {
+    .probe = virtual_key_probe,
+    .remove = virtual_key_remove,
+    .driver = {
+        .name  = "virtual_key",
+        .owner = THIS_MODULE,
+    },
+};
+
+static int __init virtual_key_init(void)
+{
+    printk("%s-%d: enter\n", __FUNCTION__, __LINE__);
+    if (platform_driver_register(&virtual_key_driver)) {
+        pr_err("virtual_key platform_driver_register  fail\n");
+        return -1;
+    }
+
+    return 0;
+}
+
+static void __exit virtual_key_exit(void)
+{
+    platform_driver_unregister(&virtual_key_driver);
+}
+
+module_init(virtual_key_init);
+module_exit(virtual_key_exit);
+
+MODULE_AUTHOR("sweetmilkcake ");
+MODULE_DESCRIPTION("virtual key driver");
+MODULE_LICENSE("GPL");
+
+

serial_comm程序

这个程序其实在另一篇文章已经介绍过，这里我把它放到system/core目录，打包到系统中，注意要在device.mk里面定义，不然全编的时候是不会编到系统的。

diff --git a/android/device/softwinner/petrel-p1/device.mk b/android/device/softwinner/petrel-p1/device.mk
index 6cb1831..9696939 100755
--- a/android/device/softwinner/petrel-p1/device.mk
+++ b/android/device/softwinner/petrel-p1/device.mk
@@ -60,6 +60,8 @@ PRODUCT_PACKAGES += \
     libip_loader \
     iploader_server
 
+PRODUCT_PACKAGES += serial_comm
+
 PRODUCT_COPY_FILES += \
     device/softwinner/petrel-p1/configs/virtual-remote.kl:system/usr/keylayout/virtual-remote.kl \
     device/softwinner/petrel-p1/configs/sunxi-keyboard.kl:system/usr/keylayout/sunxi-keyboard.kl \
diff --git a/android/system/core/serial_comm/Android.mk b/android/system/core/serial_comm/Android.mk
new file mode 100644
index 0000000..d7ee151
--- /dev/null
+++ b/android/system/core/serial_comm/Android.mk
@@ -0,0 +1,9 @@
+LOCAL_PATH := $(call my-dir)
+
+include $(CLEAR_VARS)
+LOCAL_MODULE := serial_comm
+LOCAL_SRC_FILES := serial_comm.c
+LOCAL_CFLAGS := -Wall -Werror -Wno-unused-parameter
+LOCAL_SHARED_LIBRARIES := \
+    libcutils
+include $(BUILD_EXECUTABLE)
diff --git a/android/system/core/serial_comm/serial_comm.c b/android/system/core/serial_comm/serial_comm.c
new file mode 100644
index 0000000..f40526f
--- /dev/null
+++ b/android/system/core/serial_comm/serial_comm.c
@@ -0,0 +1,212 @@
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+
+#include 
+
+#include 
+
+// dev control date end
+// 02 01 12 7F
+#define SERIAL_REC_NUM 4
+// VTIME and VMIN is very important.
+// VTIME: Time to wait for data (tenths of seconds)
+#define SERIAL_VTIME 1
+// VMIN: Minimum number of characters to read
+#define SERIAL_VMIN SERIAL_REC_NUM
+
+int serial_set(int fd, int speed, int bits, int event, int stop) {
+    struct termios ttys;
+
+    memset(&ttys, 0, sizeof(ttys));
+
+    // Enable the receiver and set local mode
+    // CLOCAL: Local line - do not change "owner" of port
+    // CREAD: Enable receiver
+    ttys.c_cflag |= (CLOCAL | CREAD);
+
+    // Mask the character size bits
+    // CSIZE: Bit mask for data bits
+    ttys.c_cflag &= ~CSIZE;
+
+    switch (speed) {
+        case 9600:
+            // B9600: 9600 baud
+            cfsetispeed(&ttys, B9600);
+            cfsetospeed(&ttys, B9600);
+            break;
+        case 115200:
+            // B115200: 115,200 baud
+            cfsetispeed(&ttys, B115200);
+            cfsetospeed(&ttys, B115200);
+            break;
+        default:
+            cfsetispeed(&ttys, B115200);
+            cfsetospeed(&ttys, B115200);
+            break;
+    }
+
+    switch (bits) {
+        case 7:
+            //     7 data bits
+            ttys.c_cflag |= CS7;
+            break;
+        case 8:
+            //     8 data bits
+            ttys.c_cflag |= CS8;
+            break;
+        default:
+            ttys.c_cflag |= CS8;
+            break;
+    }
+
+    switch (event) {
+        case 'o':
+        case 'O':
+            // PARENB: Enable parity bit
+            ttys.c_cflag |= PARENB;
+            // INPCK: Enable parity check
+            // ISTRIP: Strip parity bits
+            ttys.c_cflag |= (INPCK | ISTRIP);
+            // PARODD: Use odd parity instead of even
+            ttys.c_cflag |= PARODD;
+            break;
+        case 'e':
+        case 'E':
+            ttys.c_cflag |= PARENB;
+            ttys.c_cflag |= (INPCK | ISTRIP);
+            ttys.c_cflag &= ~PARODD;
+            break;
+        case 'n':
+        case 'N':
+            ttys.c_cflag &= ~PARENB;
+            break;
+        default:
+            ttys.c_cflag &= ~PARENB;
+            break;
+    }
+
+    switch (stop) {
+        case 1:
+            // CSTOPB:     2 stop bits (1 otherwise)
+            ttys.c_cflag &= ~CSTOPB;
+            break;
+        case 2:
+            ttys.c_cflag |= CSTOPB;
+            break;
+        default:
+            ttys.c_cflag &= ~CSTOPB;
+            break;
+    }
+
+    // VTIME: Time to wait for data (tenths of seconds)
+    ttys.c_cc[VTIME] = SERIAL_VTIME;
+    // VMIN: Minimum number of characters to read
+    ttys.c_cc[VMIN] = SERIAL_VMIN;
+
+    // Hardware flow control using the CTS (Clear To Send) and RTS (Request To Send) signal lines
+    // CNEW_RTSCTS, CRTSCTS: Enable hardware flow control (not supported on all platforms)
+    // CNEW_RTSCTS: Also called CRTSCTS
+    //ttys.c_cflag |= CRTSCTS; // Enable hardware flow control
+    ttys.c_cflag &= ~CRTSCTS; // Disable hardware flow control
+
+    // Choosing Canonical Input
+    // Canonical input is line-oriented. Input characters are put into a buffer
+    // which can be edited interactively by the user until a CR (carriage return)
+    // or LF (line feed) character is received.
+    // When selecting this mode you normally select the ICANON, ECHO, and ECHOE options
+    //ttys.c_lflag |= (ICANON | ECHO | ECHOE);
+
+    // Choosing Raw Input
+    // Raw input is unprocessed. Input characters are passed through exactly as they are received,
+    // when they are received. Generally you'll deselect the ICANON, ECHO, ECHOE, and ISIG options when using raw input
+    ttys.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);
+
+    // OPOST: Postprocess output (not set = raw output)
+    //ttys.c_oflag |= OPOST; // Choosing Processed Output
+    ttys.c_oflag &= ~OPOST; // Choosing Raw Output
+
+
+    // Flushes the input and/or output queue.
+    // TCIFLUSH: flushes data received but not read.
+    // TCOFLUSH: flushes data written but not transmitted.
+    // TCIOFLUSH: flushes both data received but not read, and data written but not transmitted.
+    tcflush(fd, TCIOFLUSH);
+
+    // Sets the serial port settings immediately.
+    // TCSANOW: Make changes now without waiting for data to complete
+    // TCSADRAIN: Wait until everything has been transmitted
+    // TCSAFLUSH: Flush input and output buffers and make the change
+    if (tcsetattr(fd, TCSANOW, &ttys) != 0) {
+        perror("serial set fail!\n");
+        return -2;
+    }
+
+    return 0;
+}
+
+int is_data_valid(unsigned char *buf) {
+    if (buf[3] != 0x7f) {
+        fprintf(stderr, "%s, data is not valid!\n", __FUNCTION__);
+        return -1;
+    }
+    return 0;
+}
+
+int main(int argc, char *argv[]) {
+    int fd = 0;
+    int ret = 0;
+    int n = 0;
+    unsigned char buf[SERIAL_REC_NUM];
+    char str[10];
+
+    printf("serial test start.\n");
+
+    fd = open("/dev/ttyS3", O_RDWR | O_NOCTTY);
+    if (fd < 0) {
+        fprintf(stderr, "%s, open serial failed!\n", __FUNCTION__);
+        return -1;
+    }
+
+    // Baud rate: 115200, Data bits: 8, Parity: None, Stop bits: 1
+    ret = serial_set(fd, 115200, 8, 'N', 1);
+    if (ret) {
+        fprintf(stderr, "%s, serial set failed!\n", __FUNCTION__);
+        return -1;
+    }
+
+    while (1) {
+        memset(&buf, 0, sizeof(buf));
+        // blocking here
+        n = read(fd, &buf, SERIAL_REC_NUM);
+        if (n < SERIAL_REC_NUM) {
+            fprintf(stderr, "serial read fail!, n = %d\n", n);
+        } else {
+            printf("buf[0] = 0x%x, buf[1] = 0x%x, buf[2] = 0x%x, buf[3] = 0x%x, \n",
+                   buf[0], buf[1], buf[2], buf[3]);
+
+            if (!is_data_valid(buf)) {
+                // data is ok
+                snprintf(str, 3, "%d", buf[2]);
+                printf("property_set persist.sys.specific_volume = %s\n", str);
+                property_set("persist.sys.specific_volume", str);
+            }
+            //n = write(fd, &buf, SERIAL_REC_NUM);
+            //if (n < SERIAL_REC_NUM) {
+            //    fprintf(stderr, "serial write fail!, n = %d\n", n);
+            //}
+        }
+    }
+
+    close(fd);
+
+    printf("serial test end.\n");
+    return 0;
+}

init进程触发逻辑

这里的逻辑是，当serial_comm进程收到串口消息会设置persist.sys.specific_volume属性，然后init进程会往/sys/kernel/virtual_key写1，然后驱动会上报键值，通知Android层，再到PhoneWindowManager进行处理。这里还要注意Selinux规则的报错，并且改了之后要全编system才可以，当时我也是调了好久。。。

 petrel-p1:/ # dmesg | grep serial                                                                                                                     
[ 0.000000] Kernel command line: earlyprintk=sunxi-uart,0x05000000 initcall_debug=0 console=ttyS0,115200 loglevel=1 root=/dev/mmcblk0p7 init=/init partitions=bootloader@mmcblk0p2:env@mmcblk0p5:boot@mmcblk0p6:system@mmcblk0p7:verity_block@mmcblk0p8:misc@mmcblk0p9:recovery@mmcblk0p10:sysrecovery@mmcblk0p11:private@mmcblk0p12:alog@mmcblk0p13:Reserve0@mmcblk0p14:Reserve1@mmcblk0p15:Reserve2@mmcblk0p16:cache@mmcblk0p17:UDISK@mmcblk0p1 cma=64M mac_addr=00:00:00:00:00:00 wifi_mac= bt_mac= selinux=1 specialstr= androidboot.selinux=permissive androidboot.serialno=dc000141091d6413078b boot_type=1 androidboot.hardware=sun50iw6p1
[ 0.822916] usbcore: registered new interface driver usbserial
[ 0.823153] usbserial: USB Serial support registered for GSM modem (1-port)
[ 2.700573] usb_serial_number:20080411
[ 6.362876] init: Service serial_comm does not have a SELinux domain defined.
[ 7.376520] init: Service serial_comm does not have a SELinux domain defined.

diff --git a/android/device/softwinner/petrel-common/sepolicy/file_contexts b/android/device/softwinner/petrel-common/sepolicy/file_contexts
index 07a6984..5414c04 100755
--- a/android/device/softwinner/petrel-common/sepolicy/file_contexts
+++ b/android/device/softwinner/petrel-common/sepolicy/file_contexts
@@ -65,3 +65,4 @@
 # optee
 /dev/opteearmtz00           u:object_r:tee_device:s0
 /system/bin/tee_supplicant  u:object_r:optee_exec:s0
+/system/bin/serial_comm     u:object_r:serial_comm_exec:s0
diff --git a/android/device/softwinner/petrel-common/sepolicy/serial_comm.te b/android/device/softwinner/petrel-common/sepolicy/serial_comm.te
new file mode 100644
index 0000000..fc0caeb
--- /dev/null
+++ b/android/device/softwinner/petrel-common/sepolicy/serial_comm.te
@@ -0,0 +1,5 @@
+type serial_comm, domain;
+type serial_comm_exec, exec_type, file_type;
+init_daemon_domain(serial_comm);
+allow serial_comm sysfs:file rw_file_perms;
+
diff --git a/android/device/softwinner/petrel-p1/init.sun50iw6p1.rc b/android/device/softwinner/petrel-p1/init.sun50iw6p1.rc
index 6d98d7a..7d99616 100755
--- a/android/device/softwinner/petrel-p1/init.sun50iw6p1.rc
+++ b/android/device/softwinner/petrel-p1/init.sun50iw6p1.rc
@@ -113,6 +113,8 @@ on boot
     write /dev/cpuset/system-background/cpus 0-3
     write /dev/cpuset/top-app/cpus 0-3
 
+    start serial_comm
+
 on property:sys.shutdown.hdmi=1
     write /sys/class/hdmi/hdmi/attr/hpd_mask 0x10
 
@@ -288,3 +290,12 @@ service stop_pppoe /system/bin/pppoe-disconnect
 service optee /system/bin/tee_supplicant
     class main
     oneshot
+
+service serial_comm /system/bin/serial_comm
+    class main
+    user root
+    disabled
+    oneshot
+
+on property:persist.sys.specific_volume=*
+    write /sys/kernel/virtual_key 1

测试

通过串口发送数据，可以直接修改Android层的音量，大功告成。

完整补丁

补丁放在：https://github.com/sweetmilkcake/AndroidPatches/blob/master/virtual-key/virtual-key.diff

写文章不易，如对您有用，麻烦给个Star，谢谢。