--- ata-all.c.orig	2009-03-15 15:49:30.000000000 +0000
+++ ata-all.c	2009-03-15 15:55:33.000000000 +0000
@@ -78,15 +78,19 @@
 int ata_dma_check_80pin = 1;
 
 /* local vars */
 static int ata_dma = 1;
+static int ata_dma_limit = 6;
 static int atapi_dma = 1;
 
 /* sysctl vars */
 SYSCTL_NODE(_hw, OID_AUTO, ata, CTLFLAG_RD, 0, "ATA driver parameters");
 TUNABLE_INT("hw.ata.ata_dma", &ata_dma);
 SYSCTL_INT(_hw_ata, OID_AUTO, ata_dma, CTLFLAG_RDTUN, &ata_dma, 0,
 	   "ATA disk DMA mode control");
+TUNABLE_INT("hw.ata.ata_dma_limit", &ata_dma_limit);
+SYSCTL_INT(_hw_ata, OID_AUTO, ata_dma_limit, CTLFLAG_RDTUN, &ata_dma_limit, 0,
+           "ATA disk DMA mode limit");
 TUNABLE_INT("hw.ata.ata_dma_check_80pin", &ata_dma_check_80pin);
 SYSCTL_INT(_hw_ata, OID_AUTO, ata_dma_check_80pin,
 	   CTLFLAG_RDTUN, &ata_dma_check_80pin, 1,
 	   "Check for 80pin cable before setting ATA DMA mode");
@@ -910,19 +914,19 @@
 int
 ata_umode(struct ata_params *ap)
 {
     if (ap->atavalid & ATA_FLAG_88) {
-	if (ap->udmamodes & 0x40)
+	if (ap->udmamodes & 0x40  &&  ata_dma_limit >= 6)
 	    return ATA_UDMA6;
-	if (ap->udmamodes & 0x20)
+	if (ap->udmamodes & 0x20  &&  ata_dma_limit >= 5)
 	    return ATA_UDMA5;
-	if (ap->udmamodes & 0x10)
+	if (ap->udmamodes & 0x10  &&  ata_dma_limit >= 4)
 	    return ATA_UDMA4;
-	if (ap->udmamodes & 0x08)
+	if (ap->udmamodes & 0x08  &&  ata_dma_limit >= 3)
 	    return ATA_UDMA3;
-	if (ap->udmamodes & 0x04)
+	if (ap->udmamodes & 0x04  &&  ata_dma_limit >= 2)
 	    return ATA_UDMA2;
-	if (ap->udmamodes & 0x02)
+	if (ap->udmamodes & 0x02  &&  ata_dma_limit >= 1)
 	    return ATA_UDMA1;
 	if (ap->udmamodes & 0x01)
 	    return ATA_UDMA0;
     }