diff --git a/drivers/scsi/ncr53c8xx.c b/drivers/scsi/ncr53c8xx.c
index fc8abe05fa8f..4458449c960b 100644
--- a/drivers/scsi/ncr53c8xx.c
+++ b/drivers/scsi/ncr53c8xx.c
@@ -514,30 +514,29 @@ static m_addr_t __vtobus(m_bush_t bush, void *m)
  *  Deal with DMA mapping/unmapping.
  */
 
-/* To keep track of the dma mapping (sg/single) that has been set */
-#define __data_mapped	SCp.phase
-#define __data_mapping	SCp.have_data_in
-
 static void __unmap_scsi_data(struct device *dev, struct scsi_cmnd *cmd)
 {
-	switch(cmd->__data_mapped) {
+	struct ncr_cmd_priv *cmd_priv = scsi_cmd_priv(cmd);
+
+	switch(cmd_priv->data_mapped) {
 	case 2:
 		scsi_dma_unmap(cmd);
 		break;
 	}
-	cmd->__data_mapped = 0;
+	cmd_priv->data_mapped = 0;
 }
 
 static int __map_scsi_sg_data(struct device *dev, struct scsi_cmnd *cmd)
 {
+	struct ncr_cmd_priv *cmd_priv = scsi_cmd_priv(cmd);
 	int use_sg;
 
 	use_sg = scsi_dma_map(cmd);
 	if (!use_sg)
 		return 0;
 
-	cmd->__data_mapped = 2;
-	cmd->__data_mapping = use_sg;
+	cmd_priv->data_mapped = 2;
+	cmd_priv->data_mapping = use_sg;
 
 	return use_sg;
 }
@@ -7854,6 +7853,7 @@ static int ncr53c8xx_slave_configure(struct scsi_device *device)
 
 static int ncr53c8xx_queue_command_lck(struct scsi_cmnd *cmd)
 {
+     struct ncr_cmd_priv *cmd_priv = scsi_cmd_priv(cmd);
      void (*done)(struct scsi_cmnd *) = scsi_done;
      struct ncb *np = ((struct host_data *) cmd->device->host->hostdata)->ncb;
      unsigned long flags;
@@ -7864,8 +7864,8 @@ printk("ncr53c8xx_queue_command\n");
 #endif
 
      cmd->host_scribble = NULL;
-     cmd->__data_mapped = 0;
-     cmd->__data_mapping = 0;
+     cmd_priv->data_mapped = 0;
+     cmd_priv->data_mapping = 0;
 
      spin_lock_irqsave(&np->smp_lock, flags);
 
@@ -8085,6 +8085,8 @@ struct Scsi_Host * __init ncr_attach(struct scsi_host_template *tpnt,
 	u_long flags = 0;
 	int i;
 
+	WARN_ON_ONCE(tpnt->cmd_size < sizeof(struct ncr_cmd_priv));
+
 	if (!tpnt->name)
 		tpnt->name	= SCSI_NCR_DRIVER_NAME;
 	if (!tpnt->shost_groups)
diff --git a/drivers/scsi/ncr53c8xx.h b/drivers/scsi/ncr53c8xx.h
index fa14b5ca8783..be38c902859e 100644
--- a/drivers/scsi/ncr53c8xx.h
+++ b/drivers/scsi/ncr53c8xx.h
@@ -1288,6 +1288,12 @@ struct ncr_device {
 	u8 differential;
 };
 
+/* To keep track of the dma mapping (sg/single) that has been set */
+struct ncr_cmd_priv {
+	int	data_mapped;
+	int	data_mapping;
+};
+
 extern struct Scsi_Host *ncr_attach(struct scsi_host_template *tpnt, int unit, struct ncr_device *device);
 extern void ncr53c8xx_release(struct Scsi_Host *host);
 irqreturn_t ncr53c8xx_intr(int irq, void *dev_id);
diff --git a/drivers/scsi/zalon.c b/drivers/scsi/zalon.c
index f1e5cf8a17d9..22d412cab91d 100644
--- a/drivers/scsi/zalon.c
+++ b/drivers/scsi/zalon.c
@@ -81,6 +81,7 @@ lasi_scsi_clock(void * hpa, int defaultclock)
 static struct scsi_host_template zalon7xx_template = {
 	.module		= THIS_MODULE,
 	.proc_name	= "zalon7xx",
+	.cmd_size	= sizeof(struct ncr_cmd_priv),
 };
 
 static int __init