scsi: ufs: commit descriptors before setting the doorbell

Add a write memory barrier to make sure descriptors prepared are
actually written to memory before ringing the doorbell. We have also
added the write memory barrier after ringing the doorbell register so
that controller sees the new request immediately.
Signed-off-by: Gilad Broner <gbroner@codeaurora.org>
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/ufs/ufshcd.c

@@ -878,6 +878,8 @@ void ufshcd_send_command(struct ufs_hba *hba, unsigned int task_tag)
 	ufshcd_clk_scaling_start_busy(hba);
 	__set_bit(task_tag, &hba->outstanding_reqs);
 	ufshcd_writel(hba, 1 << task_tag, REG_UTP_TRANSFER_REQ_DOOR_BELL);
+	/* Make sure that doorbell is committed immediately */
+	wmb();
 }
 
 /**
@@ -1475,6 +1477,8 @@ static int ufshcd_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *cmd)
 		clear_bit_unlock(tag, &hba->lrb_in_use);
 		goto out;
 	}
+	/* Make sure descriptors are ready before ringing the doorbell */
+	wmb();
 
 	/* issue command to the controller */
 	spin_lock_irqsave(hba->host->host_lock, flags);
@@ -1585,6 +1589,8 @@ static int ufshcd_wait_for_dev_cmd(struct ufs_hba *hba,
 	time_left = wait_for_completion_timeout(hba->dev_cmd.complete,
 			msecs_to_jiffies(max_timeout));
 
+	/* Make sure descriptors are ready before ringing the doorbell */
+	wmb();
 	spin_lock_irqsave(hba->host->host_lock, flags);
 	hba->dev_cmd.complete = NULL;
 	if (likely(time_left)) {
@@ -4322,6 +4328,8 @@ static int ufshcd_issue_tm_cmd(struct ufs_hba *hba, int lun_id, int task_id,
 	wmb();
 
 	ufshcd_writel(hba, 1 << free_slot, REG_UTP_TASK_REQ_DOOR_BELL);
+	/* Make sure that doorbell is committed immediately */
+	wmb();
 
 	spin_unlock_irqrestore(host->host_lock, flags);