[SCSI] remove use_sg_chaining

With the sg table code, every SCSI driver is now either chain capable
or broken (or has sg_tablesize set so chaining is never activated), so
there's no need to have a check in the host template.

Also tidy up the code by moving the scatterlist size defines into the
SCSI includes and permit the last entry of the scatterlist pools not
to be a power of two.
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

2 files changed, 19 insertions, 13 deletions

diff --git a/include/scsi/scsi.h b/include/scsi/scsi.h
index 702fcfeb37f1..0f55f5b24896 100644
--- a/include/scsi/scsi.h
+++ b/include/scsi/scsi.h
@@ -11,6 +11,25 @@
 #include <linux/types.h>
 
 /*
+ * The maximum number of SG segments that we will put inside a
+ * scatterlist (unless chaining is used). Should ideally fit inside a
+ * single page, to avoid a higher order allocation.  We could define this
+ * to SG_MAX_SINGLE_ALLOC to pack correctly at the highest order.  The
+ * minimum value is 32
+ */
+#define SCSI_MAX_SG_SEGMENTS    128
+
+/*
+ * Like SCSI_MAX_SG_SEGMENTS, but for archs that have sg chaining. This limit
+ * is totally arbitrary, a setting of 2048 will get you at least 8mb ios.
+ */
+#ifdef ARCH_HAS_SG_CHAIN
+#define SCSI_MAX_SG_CHAIN_SEGMENTS      2048
+#else
+#define SCSI_MAX_SG_CHAIN_SEGMENTS      SCSI_MAX_SG_SEGMENTS
+#endif
+
+/*
  *      SCSI command lengths
  */
 
diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index cb2bcab41dfb..5c58d594126a 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -39,9 +39,6 @@ struct blk_queue_tags;
 #define DISABLE_CLUSTERING 0
 #define ENABLE_CLUSTERING 1
 
-#define DISABLE_SG_CHAINING 0
-#define ENABLE_SG_CHAINING 1
-
 enum scsi_eh_timer_return {
         EH_NOT_HANDLED,
         EH_HANDLED,
@@ -446,15 +443,6 @@ struct scsi_host_template {
         unsigned ordered_tag:1;
 
         /*
-         * true if the low-level driver can support sg chaining. this
-         * will be removed eventually when all the drivers are
-         * converted to support sg chaining.
-         *
-         * Status: OBSOLETE
-         */
-        unsigned use_sg_chaining:1;
-
-        /*
          * Countdown for host blocking with no commands outstanding
          */
         unsigned int max_host_blocked;
@@ -598,7 +586,6 @@ struct Scsi_Host {
         unsigned unchecked_isa_dma:1;
         unsigned use_clustering:1;
         unsigned use_blk_tcq:1;
-        unsigned use_sg_chaining:1;
 
         /*
          * Host has requested that no further requests come through for the