libata-pmp-prep: implement qc_defer helpers

Implement ap->nr_active_links (the number of links with active qcs),
ap->excl_link (pointer to link which can be used by ->qc_defer and is
cleared when a qc with ATA_QCFLAG_CLEAR_EXCL completes), and
ata_link_active().

These can be used by ->qc_defer() to implement proper command
exclusion.  This set of helpers seem enough for both sil24 (ATAPI
exclusion needed) and cmd-switching PMP.

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

3 files changed, 33 insertions, 2 deletions

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index b666f51da7ed..376dbd80cc93 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -1390,6 +1390,7 @@ unsigned ata_exec_internal_sg(struct ata_device *dev,
         struct ata_queued_cmd *qc;
         unsigned int tag, preempted_tag;
         u32 preempted_sactive, preempted_qc_active;
+        int preempted_nr_active_links;
         DECLARE_COMPLETION_ONSTACK(wait);
         unsigned long flags;
         unsigned int err_mask;
@@ -1428,9 +1429,11 @@ unsigned ata_exec_internal_sg(struct ata_device *dev,
         preempted_tag = link->active_tag;
         preempted_sactive = link->sactive;
         preempted_qc_active = ap->qc_active;
+        preempted_nr_active_links = ap->nr_active_links;
         link->active_tag = ATA_TAG_POISON;
         link->sactive = 0;
         ap->qc_active = 0;
+        ap->nr_active_links = 0;
 
         /* prepare & issue qc */
         qc->tf = *tf;
@@ -1509,6 +1512,7 @@ unsigned ata_exec_internal_sg(struct ata_device *dev,
         link->active_tag = preempted_tag;
         link->sactive = preempted_sactive;
         ap->qc_active = preempted_qc_active;
+        ap->nr_active_links = preempted_nr_active_links;
 
         /* XXX - Some LLDDs (sata_mv) disable port on command failure.
          * Until those drivers are fixed, we detect the condition
@@ -5408,10 +5412,19 @@ void __ata_qc_complete(struct ata_queued_cmd *qc)
                 ata_sg_clean(qc);
 
         /* command should be marked inactive atomically with qc completion */
-        if (qc->tf.protocol == ATA_PROT_NCQ)
+        if (qc->tf.protocol == ATA_PROT_NCQ) {
                 link->sactive &= ~(1 << qc->tag);
-        else
+                if (!link->sactive)
+                        ap->nr_active_links--;
+        } else {
                 link->active_tag = ATA_TAG_POISON;
+                ap->nr_active_links--;
+        }
+
+        /* clear exclusive status */
+        if (unlikely(qc->flags & ATA_QCFLAG_CLEAR_EXCL &&
+                     ap->excl_link == link))
+                ap->excl_link = NULL;
 
         /* atapi: mark qc as inactive to prevent the interrupt handler
          * from completing the command twice later, before the error handler
@@ -5590,9 +5603,14 @@ void ata_qc_issue(struct ata_queued_cmd *qc)
 
         if (qc->tf.protocol == ATA_PROT_NCQ) {
                 WARN_ON(link->sactive & (1 << qc->tag));
+
+                if (!link->sactive)
+                        ap->nr_active_links++;
                 link->sactive |= 1 << qc->tag;
         } else {
                 WARN_ON(link->sactive);
+
+                ap->nr_active_links++;
                 link->active_tag = qc->tag;
         }
 
diff --git a/drivers/ata/libata-eh.c b/drivers/ata/libata-eh.c
index 1d3b0dccfb0a..5244723952c2 100644
--- a/drivers/ata/libata-eh.c
+++ b/drivers/ata/libata-eh.c
@@ -451,6 +451,7 @@ void ata_scsi_error(struct Scsi_Host *host)
 
                 ap->pflags |= ATA_PFLAG_EH_IN_PROGRESS;
                 ap->pflags &= ~ATA_PFLAG_EH_PENDING;
+                ap->excl_link = NULL;   /* don't maintain exclusion over EH */
 
                 spin_unlock_irqrestore(ap->lock, flags);
 
@@ -2474,6 +2475,10 @@ void ata_eh_finish(struct ata_port *ap)
                         }
                 }
         }
+
+        /* make sure nr_active_links is zero after EH */
+        WARN_ON(ap->nr_active_links);
+        ap->nr_active_links = 0;
 }
 
 /**
diff --git a/include/linux/libata.h b/include/linux/libata.h
index b0d4ca0d27b4..f9f81fd93293 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -216,6 +216,7 @@ enum {
         ATA_QCFLAG_DMAMAP       = ATA_QCFLAG_SG | ATA_QCFLAG_SINGLE,
         ATA_QCFLAG_IO           = (1 << 3), /* standard IO command */
         ATA_QCFLAG_RESULT_TF    = (1 << 4), /* result TF requested */
+        ATA_QCFLAG_CLEAR_EXCL   = (1 << 5), /* clear excl_link on completion */
 
         ATA_QCFLAG_FAILED       = (1 << 16), /* cmd failed and is owned by EH */
         ATA_QCFLAG_SENSE_VALID  = (1 << 17), /* sense data valid */
@@ -579,11 +580,13 @@ struct ata_port {
         struct ata_queued_cmd   qcmd[ATA_MAX_QUEUE];
         unsigned long           qc_allocated;
         unsigned int            qc_active;
+        int                     nr_active_links; /* #links with active qcs */
 
         struct ata_link         link;   /* host default link */
 
         int                     nr_pmp_links;   /* nr of available PMP links */
         struct ata_link         *pmp_link;      /* array of PMP links */
+        struct ata_link         *excl_link;     /* for PMP qc exclusion */
 
         struct ata_port_stats   stats;
         struct ata_host         *host;
@@ -1104,6 +1107,11 @@ static inline int ata_link_max_devices(const struct ata_link *link)
         return 1;
 }
 
+static inline int ata_link_active(struct ata_link *link)
+{
+        return ata_tag_valid(link->active_tag) || link->sactive;
+}
+
 static inline struct ata_link *ata_port_first_link(struct ata_port *ap)
 {
         if (ap->nr_pmp_links)