[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>

1 files changed, 18 insertions, 56 deletions

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 4560713ecb1..e1c7eebfe90 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));