scsi: ufs: core: Set the Command Priority (CP) flag for RT requests

Make the UFS device execute realtime (RT) requests before other requests.
This will be used in Android to reduce the I/O latency of the foreground
app.

Note: UFS devices do not support CDL so using CDL is not a viable
alternative.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20230921192335.676924-5-bvanassche@acm.org
Reviewed-by: Avri Altman <avri.altman@wdc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Author: bvanassche

drivers/ufs/core/ufshcd.c

@@ -2717,6 +2717,8 @@ static int ufshcd_compose_devman_upiu(struct ufs_hba *hba,
  */
 static void ufshcd_comp_scsi_upiu(struct ufs_hba *hba, struct ufshcd_lrb *lrbp)
 {
+	struct request *rq = scsi_cmd_to_rq(lrbp->cmd);
+	unsigned int ioprio_class = IOPRIO_PRIO_CLASS(req_get_ioprio(rq));
 	u8 upiu_flags;
 
 	if (hba->ufs_version <= ufshci_version(1, 1))
@@ -2726,6 +2728,8 @@ static void ufshcd_comp_scsi_upiu(struct ufs_hba *hba, struct ufshcd_lrb *lrbp)
 
 	ufshcd_prepare_req_desc_hdr(lrbp, &upiu_flags,
 				    lrbp->cmd->sc_data_direction, 0);
+	if (ioprio_class == IOPRIO_CLASS_RT)
+		upiu_flags |= UPIU_CMD_FLAGS_CP;
 	ufshcd_prepare_utp_scsi_cmd_upiu(lrbp, upiu_flags);
 }
 

include/ufs/ufs.h

@@ -98,9 +98,10 @@ enum upiu_response_transaction {
 	UPIU_TRANSACTION_REJECT_UPIU	= 0x3F,
 };
 
-/* UPIU Read/Write flags */
+/* UPIU Read/Write flags. See also table "UPIU Flags" in the UFS standard. */
 enum {
 	UPIU_CMD_FLAGS_NONE	= 0x00,
+	UPIU_CMD_FLAGS_CP	= 0x04,
 	UPIU_CMD_FLAGS_WRITE	= 0x20,
 	UPIU_CMD_FLAGS_READ	= 0x40,
 };