libata-pmp-prep: implement ops->qc_defer()

Controllers which support PMP have various restrictions on which
combinations of commands are allowed to what number of devices
concurrently.  This patch implements ops->qc_defer() which determines
whether a qc can be issued at the moment or should be deferred.

If the function returns ATA_DEFER_LINK, the qc will be deferred until
a qc completes on the link.  If ATA_DEFER_PORT, until a qc completes
on any link.  The defer conditions are advisory and in general
ATA_DEFER_LINK can be considered as lower priority deferring than
ATA_DEFER_PORT.

ops->qc_defer() replaces fixed ata_scmd_need_defer().  For standard
NCQ/non-NCQ exclusion, ata_std_qc_defer() is implemented.  ahci and
sata_sil24 are converted to use ata_std_qc_defer().

ops->qc_defer() is heavier than the original mechanism because full qc
is prepped before determining to defer it, but various information is
needed to determine defer conditinos and fully translating a qc is the
only way to supply such information in generic manner.

IMHO, this shouldn't cause any noticeable performance issues as

* for most cases deferring occurs rarely (except for NCQ-aware
  cmd-switching PMP)
* translation itself isn't that expensive
* once deferred the command won't be repeated until another command
  completes which usually is a very long time cpu-wise.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

6 files changed, 67 insertions, 36 deletions

diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c
index 0a6b694f0d3a..cf3404467ceb 100644
--- a/drivers/ata/ahci.c
+++ b/drivers/ata/ahci.c
@@ -268,6 +268,7 @@ static const struct ata_port_operations ahci_ops = {
 
         .tf_read                = ahci_tf_read,
 
+        .qc_defer               = ata_std_qc_defer,
         .qc_prep                = ahci_qc_prep,
         .qc_issue               = ahci_qc_issue,
 
@@ -298,6 +299,7 @@ static const struct ata_port_operations ahci_vt8251_ops = {
 
         .tf_read                = ahci_tf_read,
 
+        .qc_defer               = ata_std_qc_defer,
         .qc_prep                = ahci_qc_prep,
         .qc_issue               = ahci_qc_issue,
 
diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 9467c2f60192..b666f51da7ed 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -4346,6 +4346,36 @@ int ata_check_atapi_dma(struct ata_queued_cmd *qc)
 }
 
 /**
+ *      ata_std_qc_defer - Check whether a qc needs to be deferred
+ *      @qc: ATA command in question
+ *
+ *      Non-NCQ commands cannot run with any other command, NCQ or
+ *      not.  As upper layer only knows the queue depth, we are
+ *      responsible for maintaining exclusion.  This function checks
+ *      whether a new command @qc can be issued.
+ *
+ *      LOCKING:
+ *      spin_lock_irqsave(host lock)
+ *
+ *      RETURNS:
+ *      ATA_DEFER_* if deferring is needed, 0 otherwise.
+ */
+int ata_std_qc_defer(struct ata_queued_cmd *qc)
+{
+        struct ata_link *link = qc->dev->link;
+
+        if (qc->tf.protocol == ATA_PROT_NCQ) {
+                if (!ata_tag_valid(link->active_tag))
+                        return 0;
+        } else {
+                if (!ata_tag_valid(link->active_tag) && !link->sactive)
+                        return 0;
+        }
+
+        return ATA_DEFER_LINK;
+}
+
+/**
  *      ata_qc_prep - Prepare taskfile for submission
  *      @qc: Metadata associated with taskfile to be prepared
  *
@@ -7111,6 +7141,7 @@ EXPORT_SYMBOL_GPL(ata_interrupt);
 EXPORT_SYMBOL_GPL(ata_do_set_mode);
 EXPORT_SYMBOL_GPL(ata_data_xfer);
 EXPORT_SYMBOL_GPL(ata_data_xfer_noirq);
+EXPORT_SYMBOL_GPL(ata_std_qc_defer);
 EXPORT_SYMBOL_GPL(ata_qc_prep);
 EXPORT_SYMBOL_GPL(ata_dumb_qc_prep);
 EXPORT_SYMBOL_GPL(ata_noop_qc_prep);
diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index dc274001ddd9..8ca2caeed017 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -749,6 +749,13 @@ static void ata_scsi_sdev_config(struct scsi_device *sdev)
 {
         sdev->use_10_for_rw = 1;
         sdev->use_10_for_ms = 1;
+
+        /* Schedule policy is determined by ->qc_defer() callback and
+         * it needs to see every deferred qc.  Set dev_blocked to 1 to
+         * prevent SCSI midlayer from automatically deferring
+         * requests.
+         */
+        sdev->max_device_blocked = 1;
 }
 
 static void ata_scsi_dev_config(struct scsi_device *sdev,
@@ -1416,37 +1423,6 @@ static void ata_scsi_qc_complete(struct ata_queued_cmd *qc)
 }
 
 /**
- *      ata_scmd_need_defer - Check whether we need to defer scmd
- *      @dev: ATA device to which the command is addressed
- *      @is_io: Is the command IO (and thus possibly NCQ)?
- *
- *      NCQ and non-NCQ commands cannot run together.  As upper layer
- *      only knows the queue depth, we are responsible for maintaining
- *      exclusion.  This function checks whether a new command can be
- *      issued to @dev.
- *
- *      LOCKING:
- *      spin_lock_irqsave(host lock)
- *
- *      RETURNS:
- *      1 if deferring is needed, 0 otherwise.
- */
-static int ata_scmd_need_defer(struct ata_device *dev, int is_io)
-{
-        struct ata_link *link = dev->link;
-        int is_ncq = is_io && ata_ncq_enabled(dev);
-
-        if (is_ncq) {
-                if (!ata_tag_valid(link->active_tag))
-                        return 0;
-        } else {
-                if (!ata_tag_valid(link->active_tag) && !link->sactive)
-                        return 0;
-        }
-        return 1;
-}
-
-/**
  *      ata_scsi_translate - Translate then issue SCSI command to ATA device
  *      @dev: ATA device to which the command is addressed
  *      @cmd: SCSI command to execute
@@ -1477,14 +1453,12 @@ static int ata_scsi_translate(struct ata_device *dev, struct scsi_cmnd *cmd,
                               void (*done)(struct scsi_cmnd *),
                               ata_xlat_func_t xlat_func)
 {
+        struct ata_port *ap = dev->link->ap;
         struct ata_queued_cmd *qc;
-        int is_io = xlat_func == ata_scsi_rw_xlat;
+        int rc;
 
         VPRINTK("ENTER\n");
 
-        if (unlikely(ata_scmd_need_defer(dev, is_io)))
-                goto defer;
-
         qc = ata_scsi_qc_new(dev, cmd, done);
         if (!qc)
                 goto err_mem;
@@ -1508,6 +1482,11 @@ static int ata_scsi_translate(struct ata_device *dev, struct scsi_cmnd *cmd,
         if (xlat_func(qc))
                 goto early_finish;
 
+        if (ap->ops->qc_defer) {
+                if ((rc = ap->ops->qc_defer(qc)))
+                        goto defer;
+        }
+
         /* select device, send command to hardware */
         ata_qc_issue(qc);
 
@@ -1529,8 +1508,12 @@ err_mem:
         return 0;
 
 defer:
+        ata_qc_free(qc);
         DPRINTK("EXIT - defer\n");
-        return SCSI_MLQUEUE_DEVICE_BUSY;
+        if (rc == ATA_DEFER_LINK)
+                return SCSI_MLQUEUE_DEVICE_BUSY;
+        else
+                return SCSI_MLQUEUE_HOST_BUSY;
 }
 
 /**
@@ -3034,6 +3017,13 @@ int ata_scsi_add_hosts(struct ata_host *host, struct scsi_host_template *sht)
                 shost->max_channel = 1;
                 shost->max_cmd_len = 16;
 
+                /* Schedule policy is determined by ->qc_defer()
+                 * callback and it needs to see every deferred qc.
+                 * Set host_blocked to 1 to prevent SCSI midlayer from
+                 * automatically deferring requests.
+                 */
+                shost->max_host_blocked = 1;
+
                 rc = scsi_add_host(ap->scsi_host, ap->host->dev);
                 if (rc)
                         goto err_add;
diff --git a/drivers/ata/sata_nv.c b/drivers/ata/sata_nv.c
index b860f99fc288..40557fe2ffdf 100644
--- a/drivers/ata/sata_nv.c
+++ b/drivers/ata/sata_nv.c
@@ -423,6 +423,7 @@ static const struct ata_port_operations nv_adma_ops = {
         .bmdma_start            = ata_bmdma_start,
         .bmdma_stop             = ata_bmdma_stop,
         .bmdma_status           = ata_bmdma_status,
+        .qc_defer               = ata_std_qc_defer,
         .qc_prep                = nv_adma_qc_prep,
         .qc_issue               = nv_adma_qc_issue,
         .freeze                 = nv_adma_freeze,
diff --git a/drivers/ata/sata_sil24.c b/drivers/ata/sata_sil24.c
index d9c010ab2280..9acfce43bde4 100644
--- a/drivers/ata/sata_sil24.c
+++ b/drivers/ata/sata_sil24.c
@@ -393,6 +393,7 @@ static const struct ata_port_operations sil24_ops = {
 
         .tf_read                = sil24_tf_read,
 
+        .qc_defer               = ata_std_qc_defer,
         .qc_prep                = sil24_qc_prep,
         .qc_issue               = sil24_qc_issue,
 
diff --git a/include/linux/libata.h b/include/linux/libata.h
index c3820f105ffa..b0d4ca0d27b4 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -272,6 +272,10 @@ enum {
         /* ering size */
         ATA_ERING_SIZE          = 32,
 
+        /* return values for ->qc_defer */
+        ATA_DEFER_LINK          = 1,
+        ATA_DEFER_PORT          = 2,
+
         /* desc_len for ata_eh_info and context */
         ATA_EH_DESC_LEN         = 80,
 
@@ -639,6 +643,7 @@ struct ata_port_operations {
 
         void (*data_xfer) (struct ata_device *, unsigned char *, unsigned int, int);
 
+        int (*qc_defer) (struct ata_queued_cmd *qc);
         void (*qc_prep) (struct ata_queued_cmd *qc);
         unsigned int (*qc_issue) (struct ata_queued_cmd *qc);
 
@@ -824,6 +829,7 @@ extern void ata_data_xfer(struct ata_device *adev, unsigned char *buf,
                           unsigned int buflen, int write_data);
 extern void ata_data_xfer_noirq(struct ata_device *adev, unsigned char *buf,
                                 unsigned int buflen, int write_data);
+extern int ata_std_qc_defer(struct ata_queued_cmd *qc);
 extern void ata_dumb_qc_prep(struct ata_queued_cmd *qc);
 extern void ata_qc_prep(struct ata_queued_cmd *qc);
 extern void ata_noop_qc_prep(struct ata_queued_cmd *qc);