[libata] limit S/G table size to 128 entries

Agreeing with Ben H's recommendation, I reduce the max-hw-segments
number to 128, to match max-phys-segments number.  This shouldn't
affect performance because 128*64K is far above the max transfer size
for most current IDE devices.  Even 128*4K is OK.

drivers/scsi/ata_piix.c

@@ -89,7 +89,7 @@ static Scsi_Host_Template piix_sht = {
 	.eh_strategy_handler	= ata_scsi_error,
 	.can_queue		= ATA_DEF_QUEUE,
 	.this_id		= ATA_SHT_THIS_ID,
-	.sg_tablesize		= ATA_MAX_PRD,
+	.sg_tablesize		= LIBATA_MAX_PRD,
 	.max_sectors		= ATA_MAX_SECTORS,
 	.cmd_per_lun		= ATA_SHT_CMD_PER_LUN,
 	.emulated		= ATA_SHT_EMULATED,

drivers/scsi/libata-scsi.c

@@ -123,7 +123,7 @@ int ata_scsi_slave_config(struct scsi_device *sdev)
 {
 	sdev->use_10_for_rw = 1;
 	sdev->use_10_for_ms = 1;
-	blk_queue_max_phys_segments(sdev->request_queue, ATA_MAX_PRD / 2);
+	blk_queue_max_phys_segments(sdev->request_queue, LIBATA_MAX_PRD);
 
 	return 0;	/* scsi layer doesn't check return value, sigh */
 }

drivers/scsi/sata_promise.c

@@ -187,7 +187,7 @@ static Scsi_Host_Template pdc_sata_sht = {
 	.eh_strategy_handler	= ata_scsi_error,
 	.can_queue		= ATA_DEF_QUEUE,
 	.this_id		= ATA_SHT_THIS_ID,
-	.sg_tablesize		= ATA_MAX_PRD,
+	.sg_tablesize		= LIBATA_MAX_PRD,
 	.max_sectors		= ATA_MAX_SECTORS,
 	.cmd_per_lun		= ATA_SHT_CMD_PER_LUN,
 	.emulated		= ATA_SHT_EMULATED,

drivers/scsi/sata_sil.c

@@ -127,7 +127,7 @@ static Scsi_Host_Template sil_sht = {
 	.eh_strategy_handler	= ata_scsi_error,
 	.can_queue		= ATA_DEF_QUEUE,
 	.this_id		= ATA_SHT_THIS_ID,
-	.sg_tablesize		= ATA_MAX_PRD,
+	.sg_tablesize		= LIBATA_MAX_PRD,
 	.max_sectors		= ATA_MAX_SECTORS,
 	.cmd_per_lun		= ATA_SHT_CMD_PER_LUN,
 	.emulated		= ATA_SHT_EMULATED,

drivers/scsi/sata_svw.c

@@ -222,7 +222,7 @@ static Scsi_Host_Template k2_sata_sht = {
 	.eh_strategy_handler	= ata_scsi_error,
 	.can_queue		= ATA_DEF_QUEUE,
 	.this_id		= ATA_SHT_THIS_ID,
-	.sg_tablesize		= ATA_MAX_PRD,
+	.sg_tablesize		= LIBATA_MAX_PRD,
 	.max_sectors		= ATA_MAX_SECTORS,
 	.cmd_per_lun		= ATA_SHT_CMD_PER_LUN,
 	.emulated		= ATA_SHT_EMULATED,

drivers/scsi/sata_via.c

@@ -70,7 +70,7 @@ static Scsi_Host_Template svia_sht = {
 	.eh_strategy_handler	= ata_scsi_error,
 	.can_queue		= ATA_DEF_QUEUE,
 	.this_id		= ATA_SHT_THIS_ID,
-	.sg_tablesize		= ATA_MAX_PRD,
+	.sg_tablesize		= LIBATA_MAX_PRD,
 	.max_sectors		= ATA_MAX_SECTORS,
 	.cmd_per_lun		= ATA_SHT_CMD_PER_LUN,
 	.emulated		= ATA_SHT_EMULATED,

include/linux/libata.h

@@ -70,6 +70,7 @@
 
 enum {
 	/* various global constants */
+	LIBATA_MAX_PRD		= ATA_MAX_PRD / 2,
 	ATA_MAX_PORTS		= 8,
 	ATA_DEF_QUEUE		= 1,
 	ATA_MAX_QUEUE		= 1,