Index: dev/ic/isp_netbsd.h
===================================================================
RCS file: /cvsroot/src/sys/dev/ic/isp_netbsd.h,v
retrieving revision 1.76
diff -u -p -r1.76 isp_netbsd.h
--- dev/ic/isp_netbsd.h	20 Sep 2019 14:20:45 -0000	1.76
+++ dev/ic/isp_netbsd.h	17 Feb 2026 02:32:35 -0000
@@ -86,7 +86,8 @@ struct isposinfo {
 	uint32_t		loop_down_limit;
 	uint32_t		gone_device_time;
 	unsigned int		: 16,
-				: 8,
+				: 7,
+		use_dma64	: 1,
 		gdt_running	: 1,
 		loop_checked	: 1,
 		mbox_sleeping	: 1,
@@ -102,6 +103,7 @@ struct isposinfo {
 	uint16_t		exec_throttle;
 	struct lwp *		thread;
 };
+#define	isp_use_dma64		isp_osinfo.use_dma64
 #define	isp_dmatag		isp_osinfo.dmatag
 #define	isp_rqdmap		isp_osinfo.rqdmap
 #define	isp_rsdmap		isp_osinfo.rsdmap
Index: dev/pci/isp_pci.c
===================================================================
RCS file: /cvsroot/src/sys/dev/pci/isp_pci.c,v
retrieving revision 1.122
diff -u -p -r1.122 isp_pci.c
--- dev/pci/isp_pci.c	10 Nov 2019 21:16:36 -0000	1.122
+++ dev/pci/isp_pci.c	17 Feb 2026 02:32:36 -0000
@@ -710,7 +710,18 @@ isp_pci_attach(device_t parent, device_t
 		aprint_normal("%s", dstring);
 	}
 
-	isp->isp_dmatag = pa->pa_dmat;
+	/*
+	 * XXX isp_intr() seems to have some logic error
+	 * XXX with respect to RQSTYPE_A64, so just avoid
+	 * XXX it for now.
+	 */
+#if 0
+	if (pci_dma64_available(pa)) {
+		isp->isp_dmatag = pa->pa_dmat64;
+		isp->isp_use_dma64 = 1;
+	} else
+#endif
+		isp->isp_dmatag = pa->pa_dmat;
 	isp->isp_revision = rev;
 
 	/*
@@ -1343,7 +1354,7 @@ isp_pci_dmasetup(struct ispsoftc *isp, s
 		int error;
 		uint32_t flag, flg2;
 
-		if (sizeof (bus_addr_t) > 4) {
+		if (isp->isp_use_dma64) {
 			if (rq->req_header.rqs_entry_type == RQSTYPE_T2RQS) {
 				rq->req_header.rqs_entry_type = RQSTYPE_T3RQS;
 			} else if (rq->req_header.rqs_entry_type == RQSTYPE_REQUEST) {