ata: Enabling ATA Command Priorities

This patch checks to see if an ATA device supports NCQ command priorities.
If so and the user has specified an iocontext that indicates
IO_PRIO_CLASS_RT then we build a tf with a high priority command.

This is done to improve the tail latency of commands that are high
priority by passing priority to the device.

tj: Removed trivial ata_ncq_prio_enabled() and open-coded the test.

Signed-off-by: Adam Manzanares <adam.manzanares@hgst.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

3 files changed, 40 insertions, 3 deletions

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 223a770f78f3..8346faf63337 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -739,6 +739,7 @@ u64 ata_tf_read_block(const struct ata_taskfile *tf, struct ata_device *dev)
  *	@n_block: Number of blocks
  *	@tf_flags: RW/FUA etc...
  *	@tag: tag
+ *	@class: IO priority class
  *
  *	LOCKING:
  *	None.
@@ -753,7 +754,7 @@ u64 ata_tf_read_block(const struct ata_taskfile *tf, struct ata_device *dev)
  */
 int ata_build_rw_tf(struct ata_taskfile *tf, struct ata_device *dev,
 		    u64 block, u32 n_block, unsigned int tf_flags,
-		    unsigned int tag)
+		    unsigned int tag, int class)
 {
 	tf->flags |= ATA_TFLAG_ISADDR | ATA_TFLAG_DEVICE;
 	tf->flags |= tf_flags;
@@ -785,6 +786,12 @@ int ata_build_rw_tf(struct ata_taskfile *tf, struct ata_device *dev,
 		tf->device = ATA_LBA;
 		if (tf->flags & ATA_TFLAG_FUA)
 			tf->device |= 1 << 7;
+
+		if (dev->flags & ATA_DFLAG_NCQ_PRIO) {
+			if (class == IOPRIO_CLASS_RT)
+				tf->hob_nsect |= ATA_PRIO_HIGH <<
+						 ATA_SHIFT_PRIO;
+		}
 	} else if (dev->flags & ATA_DFLAG_LBA) {
 		tf->flags |= ATA_TFLAG_LBA;
 
@@ -2156,6 +2163,30 @@ static void ata_dev_config_ncq_non_data(struct ata_device *dev)
 	}
 }
 
+static void ata_dev_config_ncq_prio(struct ata_device *dev)
+{
+	struct ata_port *ap = dev->link->ap;
+	unsigned int err_mask;
+
+	err_mask = ata_read_log_page(dev,
+				     ATA_LOG_SATA_ID_DEV_DATA,
+				     ATA_LOG_SATA_SETTINGS,
+				     ap->sector_buf,
+				     1);
+	if (err_mask) {
+		ata_dev_dbg(dev,
+			    "failed to get Identify Device data, Emask 0x%x\n",
+			    err_mask);
+		return;
+	}
+
+	if (ap->sector_buf[ATA_LOG_NCQ_PRIO_OFFSET] & BIT(3))
+		dev->flags |= ATA_DFLAG_NCQ_PRIO;
+	else
+		ata_dev_dbg(dev, "SATA page does not support priority\n");
+
+}
+
 static int ata_dev_config_ncq(struct ata_device *dev,
 			       char *desc, size_t desc_sz)
 {
@@ -2205,6 +2236,8 @@ static int ata_dev_config_ncq(struct ata_device *dev,
 			ata_dev_config_ncq_send_recv(dev);
 		if (ata_id_has_ncq_non_data(dev->id))
 			ata_dev_config_ncq_non_data(dev);
+		if (ata_id_has_ncq_prio(dev->id))
+			ata_dev_config_ncq_prio(dev);
 	}
 
 	return 0;
diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index 9cceb4a875a5..2bccc3c7de48 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -50,6 +50,7 @@
 #include <linux/uaccess.h>
 #include <linux/suspend.h>
 #include <asm/unaligned.h>
+#include <linux/ioprio.h>
 
 #include "libata.h"
 #include "libata-transport.h"
@@ -1755,6 +1756,8 @@ static unsigned int ata_scsi_rw_xlat(struct ata_queued_cmd *qc)
 {
 	struct scsi_cmnd *scmd = qc->scsicmd;
 	const u8 *cdb = scmd->cmnd;
+	struct request *rq = scmd->request;
+	int class = IOPRIO_PRIO_CLASS(req_get_ioprio(rq));
 	unsigned int tf_flags = 0;
 	u64 block;
 	u32 n_block;
@@ -1821,7 +1824,8 @@ static unsigned int ata_scsi_rw_xlat(struct ata_queued_cmd *qc)
 	qc->nbytes = n_block * scmd->device->sector_size;
 
 	rc = ata_build_rw_tf(&qc->tf, qc->dev, block, n_block, tf_flags,
-			     qc->tag);
+			     qc->tag, class);
+
 	if (likely(rc == 0))
 		return 0;
 
diff --git a/drivers/ata/libata.h b/drivers/ata/libata.h
index 3b301a48007c..8f3a5596dd67 100644
--- a/drivers/ata/libata.h
+++ b/drivers/ata/libata.h
@@ -66,7 +66,7 @@ extern u64 ata_tf_to_lba48(const struct ata_taskfile *tf);
 extern struct ata_queued_cmd *ata_qc_new_init(struct ata_device *dev, int tag);
 extern int ata_build_rw_tf(struct ata_taskfile *tf, struct ata_device *dev,
 			   u64 block, u32 n_block, unsigned int tf_flags,
-			   unsigned int tag);
+			   unsigned int tag, int class);
 extern u64 ata_tf_read_block(const struct ata_taskfile *tf,
 			     struct ata_device *dev);
 extern unsigned ata_exec_internal(struct ata_device *dev,