CDL Feature control improvements

Control of the enable/disable state of an ATA device Command Duration Limits (CDL) features has issues:
1) Incorrect checks of the feature support for translating a MODE SELECT command
2) Incorrect feature state report translation in libata-scsi
3) The state reported when enabling the feature was being ignored, which caused needless SET FEATURES commands to be issued to the device, thus causing an unwanted reset of the CDL statistics log page (which is implied by any CDL activation action).

Patches 2 to 5 patches address these issues. In addition to these, patch 1 corrects an incorrect function return type.

Martin,

I can take the scsi patch if you are OK with it. Or the reverse, you can take all patches through the scsi tree if you prefer. Please let me know.

Changes from v2:
- Dropped the patch "ata: libata-scsi: Fail MODE SELECT for unsupported mode pages" (former patch 3) as it wasnot necessary
- Added review tag to patch 1

Changes from v1:
- Added Patch 1 and 2
- Added review tags to patches 3, 4 and 5

Damien Le Moal (4):
ata: libata-scsi: Fix ata_mselect_control_ata_feature() return type
ata: libata-scsi: Fix ata_msense_control_ata_feature()
ata: libata-scsi: Improve CDL control
scsi: Improve CDL control

 drivers/ata/libata-scsi.c | 25 +++++++++++++++++--------
 drivers/scsi/scsi.c       | 36 ++++++++++++++++++++++++------------
 2 files changed, 41 insertions(+), 20 deletions(-)

2.49.0

The function ata_mselect_control_ata_feature() has a return type defined as unsigned int but this function may return negative error codes, which are correctly propagated up the call chain as integers.

Fix ata_mselect_control_ata_feature() to have the correct int return type.

While at it, also fix a typo in this function description comment.

---
 drivers/ata/libata-scsi.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

index 2796c0da8257..24e662c837e3 100644
@@ -3886,12 +3886,11 @@ static int ata_mselect_control_spg0(struct ata_queued_cmd *qc,
 }
 
 /*
- * Translate MODE SELECT control mode page, sub-pages f2h (ATA feature mode
+ * Translate MODE SELECT control mode page, sub-page f2h (ATA feature mode
  * page) into a SET FEATURES command.
  */
-static unsigned int ata_mselect_control_ata_feature(struct ata_queued_cmd *qc,
-						    const u8 *buf, int len,
-						    u16 *fp)
+static int ata_mselect_control_ata_feature(struct ata_queued_cmd *qc,
+					   const u8 *buf, int len, u16 *fp)
 {
 	struct ata_device *dev = qc->dev;
 	struct ata_taskfile *tf = &qc->tf;

2.49.0

Nice catch!

For the ATA features subpage of the control mode page, the T10 SAT-6 specifications state that:

For a MODE SENSE command, the SATL shall return the CDL_CTRL field value that was last set by an application client.

However, the function ata_msense_control_ata_feature() always sets the CDL_CTRL field to the 0x02 value to indicate support for the CDL T2A and T2B pages. This is thus incorrect and the value 0x02 must be reported only after the user enables the CDL feature, which is indicated with the ATA_DFLAG_CDL_ENABLED device flag. When this flag is not set, the CDL_CTRL field of the ATA feature subpage of the control mode page must report a value of 0x00.

Fix ata_msense_control_ata_feature() to report the correct values for the CDL_CTRL field, according to the enable/disable state of the device CDL feature.

---
 drivers/ata/libata-scsi.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

index 24e662c837e3..a41046cb062c 100644
@@ -2453,8 +2453,8 @@ static unsigned int ata_msense_control_ata_feature(struct ata_device *dev,
 	 */
 	put_unaligned_be16(ATA_FEATURE_SUB_MPAGE_LEN - 4, &buf[2]);
 
-	if (dev->flags & ATA_DFLAG_CDL)
-		buf[4] = 0x02; /* Support T2A and T2B pages */
+	if (dev->flags & ATA_DFLAG_CDL_ENABLED)
+		buf[4] = 0x02; /* T2A and T2B pages enabled */
 	else
 		buf[4] = 0;
 

2.49.0

With ATA devices supporting the CDL feature, using CDL requires that the feature be enabled with a SET FEATURES command. This command is issued as the translated command for the MODE SELECT command issued by scsi_cdl_enable() when the user enables CDL through the device cdl_enable sysfs attribute.

Currently, ata_mselect_control_ata_feature() always translates a MODE SELECT command for the ATA features subpage of the control mode page to a SET FEATURES command to enable or disable CDL based on the cdl_ctrl field. However, there is no need to issue the SET FEATURES command if:
1) The MODE SELECT command requests disabling CDL and CDL is already disabled.
2) The MODE SELECT command requests enabling CDL and CDL is already enabled.

Fix ata_mselect_control_ata_feature() to issue the SET FEATURES command only when necessary. Since enabling CDL also implies a reset of the CDL statistics log page, avoiding useless CDL enable operations also avoids clearing the CDL statistics log.

Also add debug messages to clearly signal when CDL is being enabled or disabled using a SET FEATURES command.

---
 drivers/ata/libata-scsi.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

index a41046cb062c..c0eb8c67a9ff 100644
@@ -3908,17 +3908,27 @@ static int ata_mselect_control_ata_feature(struct ata_queued_cmd *qc,
 	/* Check cdl_ctrl */
 	switch (buf[0] & 0x03) {
 	case 0:
-		/* Disable CDL */
+		/* Disable CDL if it is enabled */
+		if (!(dev->flags & ATA_DFLAG_CDL_ENABLED))
+			return 0;
+		ata_dev_dbg(dev, "Disabling CDL\n");
 		cdl_action = 0;
 		dev->flags &= ~ATA_DFLAG_CDL_ENABLED;
 		break;
 	case 0x02:
-		/* Enable CDL T2A/T2B: NCQ priority must be disabled */
+		/*
+		 * Enable CDL if not already enabled. Since this 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");
 			return -EINVAL;
 		}
+		ata_dev_dbg(dev, "Enabling CDL\n");
 		cdl_action = 1;
 		dev->flags |= ATA_DFLAG_CDL_ENABLED;
 		break;

2.49.0

With ATA devices supporting the CDL feature, using CDL requires that the feature be enabled with a SET FEATURES command. This command is issued as the translated command for the MODE SELECT command issued by scsi_cdl_enable() when the user enables CDL through the device cdl_enable sysfs attribute.

However, the implementation of scsi_cdl_enable() always issues a MODE SELECT command for ATA devices when the enable argument is true, even if CDL is already enabled on the device. While this does not cause any issue with using CDL descriptors with read/write commands (the CDL feature will be enabled on the drive), issuing the MODE SELECT command even when the device CDL feature is already enabled will cause a reset of the ATA device CDL statistics log page (as defined in ACS, any CDL enable action must reset the device statistics).

Avoid this needless actions (and the implied statistics log page reset) by modifying scsi_cdl_enable() to issue the MODE SELECT command to enable CDL if and only if CDL is not reported as already enabled on the device.

And while at it, simplify the initialization of the is_ata boolean variable and move the declaration of the scsi mode data and sense header variables to within the scope of ATA device handling.

---
 drivers/scsi/scsi.c | 36 ++++++++++++++++++++++++------------
 1 file changed, 24 insertions(+), 12 deletions(-)

index 53daf923ad8e..518a252eb6aa 100644
@@ -707,26 +707,23 @@ void scsi_cdl_check(struct scsi_device *sdev)
  */
 int scsi_cdl_enable(struct scsi_device *sdev, bool enable)
 {
-	struct scsi_mode_data data;
-	struct scsi_sense_hdr sshdr;
-	struct scsi_vpd *vpd;
-	bool is_ata = false;
 	char buf[64];
+	bool is_ata;
 	int ret;
 
 	if (!sdev->cdl_supported)
 		return -EOPNOTSUPP;
 
 	rcu_read_lock();
-	vpd = rcu_dereference(sdev->vpd_pg89);
-	if (vpd)
-		is_ata = true;
+	is_ata = rcu_dereference(sdev->vpd_pg89);
 	rcu_read_unlock();
 
 	/*
 	 * For ATA devices, CDL needs to be enabled with a SET FEATURES command.
 	 */
 	if (is_ata) {
+		struct scsi_mode_data data;
+		struct scsi_sense_hdr sshdr;
 		char *buf_data;
 		int len;
 

@@ -735,16 +732,30 @@ int scsi_cdl_enable(struct scsi_device *sdev, bool enable)
 		if (ret)
 			return -EINVAL;
 
-		/* Enable CDL using the ATA feature page */
+		/* Enable or disable CDL using the ATA feature page */
 		len = min_t(size_t, sizeof(buf),
 			    data.length - data.header_length -
 			    data.block_descriptor_length);
 		buf_data = buf + data.header_length +
 			data.block_descriptor_length;
-		if (enable)
-			buf_data[4] = 0x02;
-		else
-			buf_data[4] = 0;
+
+		/*
+		 * If we want to enable CDL and CDL is already enabled on the
+		 * device, do nothing. This avoids needlessly resetting the CDL
+		 * statistics on the device as that is implied by the CDL enable
+		 * action. Similar to this, there is no need to do anything if
+		 * we want to disable CDL and CDL is already disabled.
+		 */
+		if (enable) {
+			if ((buf_data[4] & 0x03) == 0x02)
+				goto out;
+			buf_data[4] &= ~0x03;
+			buf_data[4] |= 0x02;
+		} else {
+			if ((buf_data[4] & 0x03) == 0x00)
+				goto out;
+			buf_data[4] &= ~0x03;
+		}
 
 		ret = scsi_mode_select(sdev, 1, 0, buf_data, len, 5 * HZ, 3,
 				       &data, &sshdr);

@@ -756,6 +767,7 @@ int scsi_cdl_enable(struct scsi_device *sdev, bool enable)
 		}
 	}
 
+out:
 	sdev->cdl_enable = enable;
 
 	return 0;

2.49.0

Damien,

Feel free to take this series through ATA.

Martin K. Petersen