UFS发生命令超时处理流程

1. 在UFS的上层发送命令下来，如果上层30s没有收到ufs devices的response, 就会出现超时，此时会去查询命令是否真正的发送以及是否需要Abort 超时的命令

首先我们先看数据传输是驱动程序的本质目的，通过数据的传输，来完成作为存储介质的使命，read & write，在read流程中，ufs向应用程序提供数据，在write流程中，应用程序向ufs存放数据。

本节分三个阶段关注数据的流向，分别是：系统调用数据到bio的组成，bio到电梯队列request的组成，request到controller的数据传输。主要围绕buffer和存储地址两个数据流要素，根据读流程描述各阶段这两个数据流要素的数据结构。

sys_read->submit_bio的流程

bio生成后，就plug到进程的plug_list里面，如果失败，则进电梯merge，如果依然失败，则只能等待新的request被释放出来，两次蓄流的目的是为了尽可能的让bio请求得到merge，减少往磁盘驱动下发的频度，提升综合性能

bio层->request的流程

当plug_list达到设定阈值或进程主动发起或设定时间已到或手机将要关机等，则会进行泄流。从elevator的queue里面取出一个request请求，下发到底层UFS驱动，这个流程从request转化为scsi协议包，最后封装在UFS的协议包UPIU包里面，于是就完成了一个请求的host内存准备，最后通过置这个请求对应的UFSHCI的doorbell寄存器中的mask，实现请求往驱动层的发送。

2. 接下来我们看看超时的具体流程和操作

```c
/**
* scsi_alloc_sdev - allocate and setup a scsi_Device
* @starget: which target to allocate a &scsi_device for
* @lun: which lun
* @hostdata: usually NULL and set by ->slave_alloc instead
*
* Description:
* Allocate, initialize for io, and return a pointer to a scsi_Device.
* Stores the @shost, @channel, @id, and @lun in the scsi_Device, and
* adds scsi_Device to the appropriate list.
*
* Return value:
* scsi_Device pointer, or NULL on failure.
**/

```

/**
* ufshcd_abort - abort a specific command
* @cmd: SCSI command pointer
*
* Abort the pending command in device by sending UFS_ABORT_TASK task management
* command, and in host controller by clearing the door-bell register. There can
* be race between controller sending the command to the device while abort is
* issued. To avoid that, first issue UFS_QUERY_TASK to check if the command is
* really issued and then try to abort it.
*
* Returns SUCCESS/FAILED
*/
static int ufshcd_abort(struct scsi_cmnd *cmd)
{
   struct Scsi_Host *host;
   struct ufs_hba *hba;
   unsigned long flags;
   unsigned int tag;
   int err = 0;
   int poll_cnt;
   u8 resp = 0xF;
   struct ufshcd_lrb *lrbp;
   u32 reg;

host = cmd->device->host;
   hba = shost_priv(host);
   tag = cmd->request->tag;
   lrbp = &hba->lrb[tag];
   if (!ufshcd_valid_tag(hba, tag)) {
       dev_err(hba->dev,
           "%s: invalid command tag %d: cmd=0x%p, cmd->request=0x%p",
           __func__, tag, cmd, cmd->request);
       BUG();
   }

/*
   * Task abort to the device W-LUN is illegal. When this command
   * will fail, due to spec violation, scsi err handling next step
   * will be to send LU reset which, again, is a spec violation.
   * To avoid these unnecessary/illegal step we skip to the last error
   * handling stage: reset and restore.
   */
   if (lrbp->lun == UFS_UPIU_UFS_DEVICE_WLUN)
       return ufshcd_eh_host_reset_handler(cmd);

ufshcd_hold(hba, false);
   reg = ufshcd_readl(hba, REG_UTP_TRANSFER_REQ_DOOR_BELL);
   /* If command is already aborted/completed, return SUCCESS */
   if (!(test_bit(tag, &hba->outstanding_reqs))) {
       dev_err(hba->dev,
           "%s: cmd at tag %d already completed, outstanding=0x%lx, doorbell=0x%x\n",
           __func__, tag, hba->outstanding_reqs, reg);
       goto out;
   }

if (!(reg & (1 << tag))) {
       dev_err(hba->dev,
       "%s: cmd was completed, but without a notifying intr, tag = %d",
       __func__, tag);
   }

/* Print Transfer Request of aborted task */
dev_err(hba->dev, "%s: Device abort task at tag %d\n", __func__, tag);

/*
   * Print detailed info about aborted request.
   * As more than one request might get aborted at the same time,
   * print full information only for the first aborted request in order
   * to reduce repeated printouts. For other aborted requests only print
   * basic details.
   */
   scsi_print_command(hba->lrb[tag].cmd);
   if (!hba->req_abort_count) {
       ufshcd_print_host_regs(hba);
       ufshcd_print_host_state(hba);
       ufshcd_print_pwr_info(hba);
       ufshcd_print_trs(hba, 1 << tag, true);
   } else {
       ufshcd_print_trs(hba, 1 << tag, false);
   }
   hba->req_abort_count++;

/* Skip task abort in case previous aborts failed and report failure */
   if (lrbp->req_abort_skip) {
       err = -EIO;
       goto out;
   }

for (poll_cnt = 100; poll_cnt; poll_cnt--) {
       err = ufshcd_issue_tm_cmd(hba, lrbp->lun, lrbp->task_tag,
               UFS_QUERY_TASK, &resp);
       if (!err && resp == UPIU_TASK_MANAGEMENT_FUNC_SUCCEEDED) {
           /* cmd pending in the device */
           dev_err(hba->dev, "%s: cmd pending in the device. tag = %d\n",
               __func__, tag);
           break;
       } else if (!err && resp == UPIU_TASK_MANAGEMENT_FUNC_COMPL) {
           /*
           * cmd not pending in the device, check if it is
           * in transition.
           */
           dev_err(hba->dev, "%s: cmd at tag %d not pending in the device.\n",
               __func__, tag);
           reg = ufshcd_readl(hba, REG_UTP_TRANSFER_REQ_DOOR_BELL);
           if (reg & (1 << tag)) {
               /* sleep for max. 200us to stabilize */
               usleep_range(100, 200);
               continue;
           }
           /* command completed already */
           dev_err(hba->dev, "%s: cmd at tag %d successfully cleared from DB.\n",
               __func__, tag);
           goto out;
       } else {
           dev_err(hba->dev,
               "%s: no response from device. tag = %d, err %d\n",
               __func__, tag, err);
           if (!err)
               err = resp; /* service response error */
           goto out;
       }
   }

if (!poll_cnt) {
       err = -EBUSY;
       goto out;
   }

err = ufshcd_issue_tm_cmd(hba, lrbp->lun, lrbp->task_tag,
           UFS_ABORT_TASK, &resp);
   if (err || resp != UPIU_TASK_MANAGEMENT_FUNC_COMPL) {
       if (!err) {
           err = resp; /* service response error */
           dev_err(hba->dev, "%s: issued. tag = %d, err %d\n",
               __func__, tag, err);
       }
       goto out;
   }

err = ufshcd_clear_cmd(hba, tag);
   if (err) {
       dev_err(hba->dev, "%s: Failed clearing cmd at tag %d, err %d\n",
           __func__, tag, err);
       goto out;
   }

scsi_dma_unmap(cmd);

spin_lock_irqsave(host->host_lock, flags);
   ufshcd_outstanding_req_clear(hba, tag);
   hba->lrb[tag].cmd = NULL;
   spin_unlock_irqrestore(host->host_lock, flags);

clear_bit_unlock(tag, &hba->lrb_in_use);
wake_up(&hba->dev_cmd.tag_wq);

out:
   if (!err) {
       err = SUCCESS;
   } else {
       dev_err(hba->dev, "%s: failed with err %d\n", __func__, err);
       ufshcd_set_req_abort_skip(hba, hba->outstanding_reqs);
       err = FAILED;
   }

/*
   * This ufshcd_release() corresponds to the original scsi cmd that got
   * aborted here (as we won't get any IRQ for it).
   */
   ufshcd_release(hba);
   return err;
}

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