1 files changed, 18 insertions, 56 deletions

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 4560713ecb14..e1c7eebfe907 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -8,6 +8,7 @@
  */
 
 #include <linux/bio.h>
+#include <linux/bitops.h>
 #include <linux/blkdev.h>
 #include <linux/completion.h>
 #include <linux/kernel.h>
@@ -34,13 +35,6 @@
 #define SG_MEMPOOL_NR           ARRAY_SIZE(scsi_sg_pools)
 #define SG_MEMPOOL_SIZE         2
 
-/*
- * 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.
- */
-#define SCSI_MAX_SG_SEGMENTS    128
-
 struct scsi_host_sg_pool {
         size_t          size;
         char            *name;
@@ -48,19 +42,26 @@ struct scsi_host_sg_pool {
         mempool_t       *pool;
 };
 
-#define SP(x) { x, "sgpool-" #x }
+#define SP(x) { x, "sgpool-" __stringify(x) }
+#if (SCSI_MAX_SG_SEGMENTS < 32)
+#error SCSI_MAX_SG_SEGMENTS is too small (must be 32 or greater)
+#endif
 static struct scsi_host_sg_pool scsi_sg_pools[] = {
         SP(8),
         SP(16),
-#if (SCSI_MAX_SG_SEGMENTS > 16)
-        SP(32),
 #if (SCSI_MAX_SG_SEGMENTS > 32)
-        SP(64),
+        SP(32),
 #if (SCSI_MAX_SG_SEGMENTS > 64)
+        SP(64),
+#if (SCSI_MAX_SG_SEGMENTS > 128)
         SP(128),
+#if (SCSI_MAX_SG_SEGMENTS > 256)
+#error SCSI_MAX_SG_SEGMENTS is too large (256 MAX)
 #endif
 #endif
 #endif
+#endif
+        SP(SCSI_MAX_SG_SEGMENTS)
 };
 #undef SP
 
@@ -692,42 +693,16 @@ static struct scsi_cmnd *scsi_end_request(struct scsi_cmnd *cmd, int error,
         return NULL;
 }
 
-/*
- * 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.
- */
-#define SCSI_MAX_SG_CHAIN_SEGMENTS      2048
-
 static inline unsigned int scsi_sgtable_index(unsigned short nents)
 {
         unsigned int index;
 
-        switch (nents) {
-        case 1 ... 8:
+        BUG_ON(nents > SCSI_MAX_SG_SEGMENTS);
+
+        if (nents <= 8)
                 index = 0;
-                break;
-        case 9 ... 16:
-                index = 1;
-                break;
-#if (SCSI_MAX_SG_SEGMENTS > 16)
-        case 17 ... 32:
-                index = 2;
-                break;
-#if (SCSI_MAX_SG_SEGMENTS > 32)
-        case 33 ... 64:
-                index = 3;
-                break;
-#if (SCSI_MAX_SG_SEGMENTS > 64)
-        case 65 ... 128:
-                index = 4;
-                break;
-#endif
-#endif
-#endif
-        default:
-                printk(KERN_ERR "scsi: bad segment count=%d\n", nents);
-                BUG();
-        }
+        else
+                index = get_count_order(nents) - 3;
 
         return index;
 }
@@ -1603,20 +1578,7 @@ struct request_queue *__scsi_alloc_queue(struct Scsi_Host *shost,
          * this limit is imposed by hardware restrictions
          */
         blk_queue_max_hw_segments(q, shost->sg_tablesize);
-
-        /*
-         * In the future, sg chaining support will be mandatory and this
-         * ifdef can then go away. Right now we don't have all archs
-         * converted, so better keep it safe.
-         */
-#ifdef ARCH_HAS_SG_CHAIN
-        if (shost->use_sg_chaining)
-                blk_queue_max_phys_segments(q, SCSI_MAX_SG_CHAIN_SEGMENTS);
-        else
-                blk_queue_max_phys_segments(q, SCSI_MAX_SG_SEGMENTS);
-#else
-        blk_queue_max_phys_segments(q, SCSI_MAX_SG_SEGMENTS);
-#endif
+        blk_queue_max_phys_segments(q, SCSI_MAX_SG_CHAIN_SEGMENTS);
 
         blk_queue_max_sectors(q, shost->max_sectors);
         blk_queue_bounce_limit(q, scsi_calculate_bounce_limit(shost));