高通平台开发系列讲解（USB篇）port_bridge转发应用分析

Posted 2022-05-24 内核笔记

文章目录

• 一、图解port_bridge作用
• 二、port_bridge入口分析
• 三、usb_to_modem_bridge线程
• 四、/dev/at_mdm0处理AT指令

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📢本篇章主要介绍高通平台USB数据转发给modem流程。

一、图解port_bridge作用

---

port_bridge的功能是将从USB接受到的数据转发至SMD，该阶段在linux debug口上进行排查，通过分析port_bridge进程的状态及执行log，定位问题发生位置。

二、port_bridge入口分析

---

目录：apps_proc/data/port-bridge/port_bridge.c

int main()

 
  pthread_t mdm_thread, usb_thread;
  thread_info_t mdm_info, usb_info;
 
 /* MDM -> USB info object */
  mdm_info.from_fd        = &mdm_fd;
  mdm_info.to_fd          = &usb_fd;
  mdm_info.to_file_path   = targetinfo.usb_chardev;
  mdm_info.from_file_path = targetinfo.mdm_chardev;
  mdm_info.to_mutex       = &usb_mutex;
  mdm_info.from_mutex     = &mdm_mutex;
 
  /* USB -> MDM info object */
  usb_info.from_fd        = &usb_fd;
  usb_info.to_fd          = &mdm_fd;
  usb_info.from_file_path = targetinfo.usb_chardev;
  usb_info.to_file_path   = targetinfo.mdm_chardev;
  usb_info.to_mutex       = &mdm_mutex;
  usb_info.from_mutex     = &usb_mutex;
 
  pthread_create(&mdm_thread, NULL, targetinfo.mdm_handler, &mdm_info);
  pthread_create(&usb_thread,  NULL, usb_to_modem_bridge, &usb_info);
 
  pthread_join(mdm_thread,  NULL);
  pthread_join(usb_thread,   NULL);
 

三、usb_to_modem_bridge线程

---

USB -> MDM这里操作的 glink_pkt

void* usb_to_modem_bridge(void* thread_info)

  thread_info_t tinfo   = *((thread_info_t*)thread_info);
  while (1)
  
    /* ####### OPEN THE USB FILE ####### */
    if (*tinfo.from_fd < 0)
    
        temp_fd = open(tinfo.from_file_path, O_RDWR);  /* Custom blocking open */
    
    while (glink_rx_intent_count < GLINK_RX_INTENT_MIN)
    
      unsigned int rx_packet_max_size = MAX_MSG_SIZE;
 
      LOGI("Queuing RX Intent for '%s'\\n", tinfo.from_file_path);
      PB_PTHREAD_MUTEX_LOCK(tinfo.from_mutex, tinfo.from_file_path);
      ret = ioctl(*tinfo.from_fd, GLINK_PKT_IOCTL_QUEUE_RX_INTENT, &rx_packet_max_size);
      PB_PTHREAD_MUTEX_UNLOCK(tinfo.from_mutex, tinfo.from_file_path);
      if (ret)
      
        LOGE("Error queuing RX intent=%d\\n", ret);
        exit(1);
      
      glink_rx_intent_count++;
    
 
    // At this point it's open, so poll for anything we need to do
    pollinfo.revents = 0;
    LOGI("Attempting to poll '%s'...\\n", tinfo.from_file_path);
    ret = poll(&pollinfo, 1, -1); // -1 timeout specifies infinite block (default linux behavior)
    LOGR(ret, "poll on '%s' returned %i\\n", tinfo.from_file_path, ret);
 

四、/dev/at_mdm0处理AT指令

前面分析到port_bridge进程会将从PC发过来的数据写入到/dev/at_mdm0中，那么这个过程又是怎样的呢？/dev/at_mdm0驱动代码位于drivers/soc/qcom/glink_pkt.c，写入的时候最终会调用glink_pkt_write, glink_pkt_write的流程如下:

ssize_t glink_pkt_write(struct file *file, const char __user *buf,
                        size_t count, loff_t *ppos)

        struct glink_pkt_device *gpdev = file->private_data;
        void *kbuf;
        int ret;
 
        gpdev = file->private_data;
        if (!gpdev || refcount_read(&gpdev->refcount) == 1) 
                GLINK_PKT_ERR("invalid device handle\\n");
                return -EINVAL;
        
 
        GLINK_PKT_INFO("begin to %s buffer_size %zu\\n", gpdev->ch_name, count);
        kbuf = memdup_user(buf, count);
        if (IS_ERR(kbuf))
                return PTR_ERR(kbuf);
 
        if (mutex_lock_interruptible(&gpdev->lock)) 
                ret = -ERESTARTSYS;
                goto free_kbuf;
        
        if (!completion_done(&gpdev->ch_open) || !gpdev->rpdev) 
                GLINK_PKT_ERR("%s channel in reset\\n", gpdev->ch_name);
                ret = -ENETRESET;
                goto unlock_ch;
        
 
        if (file->f_flags & O_NONBLOCK)
                ret = rpmsg_trysend(gpdev->rpdev->ept, kbuf, count);
        else
                ret = rpmsg_send(gpdev->rpdev->ept, kbuf, count);
 
unlock_ch:
        mutex_unlock(&gpdev->lock);
 
free_kbuf:
        kfree(kbuf);
        GLINK_PKT_INFO("finish to %s ret %d\\n", gpdev->ch_name, ret);
        return ret < 0 ? ret : count;

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