[PATCH 4/6] scsi: storvsc: use tagged SRB requests if supported by the device

[Tim Gardner]

From: Long Li <longli at microsoft.com>

BugLink: http://bugs.launchpad.net/bugs/1663687

Properly set SRB flags when hosting device supports tagged queuing.
This patch improves the performance on Fiber Channel disks.

Signed-off-by: Long Li <longli at microsoft.com>
Reviewed-by: K. Y. Srinivasan <kys at microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys at microsoft.com>
Cc: <stable at vger.kernel.org>
Signed-off-by: Martin K. Petersen <martin.petersen at oracle.com>
(cherry picked from commit 3cd6d3d9b1abab8dcdf0800224ce26daac24eea2)
Signed-off-by: Tim Gardner <tim.gardner at canonical.com>
---
 drivers/scsi/storvsc_drv.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
index c54b726..094573d 100644
--- a/drivers/scsi/storvsc_drv.c
+++ b/drivers/scsi/storvsc_drv.c
@@ -136,6 +136,8 @@ struct hv_fc_wwn_packet {
 #define SRB_FLAGS_PORT_DRIVER_RESERVED		0x0F000000
 #define SRB_FLAGS_CLASS_DRIVER_RESERVED		0xF0000000
 
+#define SP_UNTAGGED			((unsigned char) ~0)
+#define SRB_SIMPLE_TAG_REQUEST		0x20
 
 /*
  * Platform neutral description of a scsi request -
@@ -1549,6 +1551,13 @@ static int storvsc_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *scmnd)
 	vm_srb->win8_extension.srb_flags |=
 		SRB_FLAGS_DISABLE_SYNCH_TRANSFER;
 
+	if (scmnd->device->tagged_supported) {
+		vm_srb->win8_extension.srb_flags |=
+		(SRB_FLAGS_QUEUE_ACTION_ENABLE | SRB_FLAGS_NO_QUEUE_FREEZE);
+		vm_srb->win8_extension.queue_tag = SP_UNTAGGED;
+		vm_srb->win8_extension.queue_action = SRB_SIMPLE_TAG_REQUEST;
+	}
+
 	/* Build the SRB */
 	switch (scmnd->sc_data_direction) {
 	case DMA_TO_DEVICE:
-- 
2.7.4