scsi: ufs: Inform the block layer about write ordering

From the UFSHCI 4.0 specification, about the MCQ mode:
"Command Submission
1. Host SW writes an Entry to SQ
2. Host SW updates SQ doorbell tail pointer

Command Processing
3. After fetching the Entry, Host Controller updates SQ doorbell head
   pointer
4. Host controller sends COMMAND UPIU to UFS device"

In other words, in MCQ mode, UFS controllers are required to forward
commands to the UFS device in the order these commands have been
received from the host.

This patch improves performance as follows on a test setup with UFSHCI
4.0 controller:
- When not using an I/O scheduler: 2.3x more IOPS for small writes.
- With the mq-deadline scheduler: 2.0x more IOPS for small writes.

Reviewed-by: Avri Altman <[email protected]>
Cc: Bao D. Nguyen <[email protected]>
Cc: Can Guo <[email protected]>
Cc: Martin K. Petersen <[email protected]>
Signed-off-by: Bart Van Assche <[email protected]>

Author: bvanassche

drivers/ufs/core/ufshcd.c

@@ -5281,6 +5281,12 @@ static int ufshcd_sdev_configure(struct scsi_device *sdev,
 	struct ufs_hba *hba = shost_priv(sdev->host);
 	struct request_queue *q = sdev->request_queue;
 
+	/*
+	 * The write order is preserved per MCQ. Without MCQ, auto-hibernation
+	 * may cause write reordering that results in unaligned write errors.
+	 */
+	lim->driver_preserves_write_order = hba->mcq_enabled;
+
 	lim->dma_pad_mask = PRDT_DATA_BYTE_COUNT_PAD - 1;
 
 	/*