[PATCH v2] ata: libata-scsi: Fix CDL control

[Igor Pylypiv <ipylypiv@google.com>]

Delete extra checks for the ATA_DFLAG_CDL_ENABLED flag that prevent
SET FEATURES command from being issued to a drive when NCQ commands
are active.

ata_mselect_control_ata_feature() sets / clears the ATA_DFLAG_CDL_ENABLED
flag during the translation of MODE SELECT to SET FEATURES. If SET FEATURES
gets deferred due to outstanding NCQ commands, the original MODE SELECT
command will be re-queued. When the re-queued MODE SELECT goes through
the ata_mselect_control_ata_feature() translation again, SET FEATURES
will not be issued because ATA_DFLAG_CDL_ENABLED has been already set or
cleared by the initial translation of MODE SELECT.

The ATA_DFLAG_CDL_ENABLED checks in ata_mselect_control_ata_feature()
are safe to remove because scsi_cdl_enable() implements a similar logic
that avoids enabling CDL if it has been enabled already.

Fixes: 17e897a45675 ("ata: libata-scsi: Improve CDL control")
Signed-off-by: Igor Pylypiv <ipylypiv@google.com>
---

Changes from v1:
- Changed the patch from revert to fixup.
- Restored debug logs and the comment about mutual exclusivity with
  NCQ priority.
- Dropped cc to stable and added fixes tag instead.

 drivers/ata/libata-scsi.c | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index 57f674f51b0c..2ded5e476d6e 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -3904,21 +3904,16 @@ static int ata_mselect_control_ata_feature(struct ata_queued_cmd *qc,
 	/* Check cdl_ctrl */
 	switch (buf[0] & 0x03) {
 	case 0:
-		/* Disable CDL if it is enabled */
-		if (!(dev->flags & ATA_DFLAG_CDL_ENABLED))
-			return 0;
+		/* Disable CDL */
 		ata_dev_dbg(dev, "Disabling CDL\n");
 		cdl_action = 0;
 		dev->flags &= ~ATA_DFLAG_CDL_ENABLED;
 		break;
 	case 0x02:
 		/*
-		 * Enable CDL if not already enabled. Since this is mutually
-		 * exclusive with NCQ priority, allow this only if NCQ priority
-		 * is disabled.
+		 * Enable CDL. Since CDL is mutually exclusive with NCQ
+		 * priority, allow this only if NCQ priority is disabled.
 		 */
-		if (dev->flags & ATA_DFLAG_CDL_ENABLED)
-			return 0;
 		if (dev->flags & ATA_DFLAG_NCQ_PRIO_ENABLED) {
 			ata_dev_err(dev,
 				"NCQ priority must be disabled to enable CDL\n");
-- 
2.51.0.rc0.215.g125493bb4a-goog