[SCSI] add shared tag map helpers

This patch adds support for sharing tag maps at the host level
(i.e. either every queue [LUN] has its own tag map or there's a single
one for the entire host).  This formulation is primarily intended to
help single issue queue hardware, like the aic7xxx

Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

2 files changed, 20 insertions, 1 deletions

diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index b3dd90f3e858..39c6f8cc20c3 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -16,6 +16,7 @@ struct scsi_target;
 struct Scsi_Host;
 struct scsi_host_cmd_pool;
 struct scsi_transport_template;
+struct blk_queue_tags;
 
 
 /*
@@ -466,6 +467,12 @@ struct Scsi_Host {
         struct scsi_transport_template *transportt;
 
         /*
+         * area to keep a shared tag map (if needed, will be
+         * NULL if not)
+         */
+        struct blk_queue_tag    *bqt;
+
+        /*
          * The following two fields are protected with host_lock;
          * however, eh routines can safely access during eh processing
          * without acquiring the lock.
diff --git a/include/scsi/scsi_tcq.h b/include/scsi/scsi_tcq.h
index e47e36a4ef49..4eea254b1ce9 100644
--- a/include/scsi/scsi_tcq.h
+++ b/include/scsi/scsi_tcq.h
@@ -4,6 +4,7 @@
 #include <linux/blkdev.h>
 #include <scsi/scsi_cmnd.h>
 #include <scsi/scsi_device.h>
+#include <scsi/scsi_host.h>
 
 
 #define MSG_SIMPLE_TAG  0x20
@@ -66,7 +67,8 @@ static inline void scsi_activate_tcq(struct scsi_device *sdev, int depth)
                 return;
 
         if (!blk_queue_tagged(sdev->request_queue))
-                blk_queue_init_tags(sdev->request_queue, depth, NULL);
+                blk_queue_init_tags(sdev->request_queue, depth,
+                                    sdev->host->bqt);
 
         scsi_adjust_queue_depth(sdev, scsi_get_tag_type(sdev), depth);
 }
@@ -131,4 +133,14 @@ static inline struct scsi_cmnd *scsi_find_tag(struct scsi_device *sdev, int tag)
         return sdev->current_cmnd;
 }
 
+/**
+ * scsi_init_shared_tag_map - create a shared tag map
+ * @shost:      the host to share the tag map among all devices
+ * @depth:      the total depth of the map
+ */
+static inline void scsi_init_shared_tag_map(struct Scsi_Host *shost, int depth)
+{
+        shost->bqt = blk_init_tags(depth);
+}
+
 #endif /* _SCSI_SCSI_TCQ_H */