Index: dev/ata/ata-disk.c
===================================================================
RCS file: /home/ncvs/src/sys/dev/ata/ata-disk.c,v
retrieving revision 1.83
diff -u -r1.83 ata-disk.c
--- dev/ata/ata-disk.c	2000/10/17 10:05:47	1.83
+++ dev/ata/ata-disk.c	2000/10/17 23:13:58
@@ -41,6 +41,7 @@
 #include <sys/disk.h>
 #include <sys/devicestat.h>
 #include <sys/cons.h>
+#include <sys/sysctl.h>
 #include <vm/vm.h>
 #include <vm/pmap.h>
 #include <machine/md_var.h>
@@ -89,6 +90,9 @@
 /* experimental cache flush on BIO_ORDERED */
 #define ATA_FLUSHCACHE_ON 
 
+int ad_wce = 0;
+SYSCTL_INT(_hw, OID_AUTO, ad_wce, CTLFLAG_RW, &ad_wce, 0, "");
+
 void
 ad_attach(struct ata_softc *scp, int device)
 {
@@ -135,9 +139,11 @@
 		    0, 0, 0, 0, ATA_C_F_ENAB_RCACHE, ATA_WAIT_INTR))
 	printf("ad%d: enabling readahead cache failed\n", adp->lun);
 
+#if 0
     if (ata_command(adp->controller, adp->unit, ATA_C_SETFEATURES,
 		    0, 0, 0, 0, ATA_C_F_ENAB_WCACHE, ATA_WAIT_INTR))
 	printf("ad%d: enabling write cache failed\n", adp->lun);
+#endif
 
     /* use DMA if drive & controller supports it */
     ata_dmainit(adp->controller, adp->unit,
@@ -331,6 +337,15 @@
     struct bio *bp = bioq_first(&adp->queue);
     struct ad_request *request;
     int tag = 0;
+
+    if (adp->wce != ad_wce) {
+	printf("ad%d: %sabling write cache\n", adp->lun, ad_wce ? "en":"dis");
+	ata_command(adp->controller, adp->unit, ATA_C_SETFEATURES,
+		    0, 0, 0, 0, ad_wce ? ATA_C_F_ENAB_WCACHE :
+		    			 ATA_C_F_DIS_WCACHE, ATA_IMMEDIATE);
+	adp->wce = ad_wce;
+	return;
+    }
 
     if (!bp)
 	return;
Index: dev/ata/ata-disk.h
===================================================================
RCS file: /home/ncvs/src/sys/dev/ata/ata-disk.h,v
retrieving revision 1.30
diff -u -r1.30 ata-disk.h
--- dev/ata/ata-disk.h	2000/10/13 13:04:45	1.30
+++ dev/ata/ata-disk.h	2000/10/17 23:13:58
@@ -71,6 +71,7 @@
 
     struct ad_request		*tags[32];	/* tag array of requests */
     int				outstanding;	/* tags not serviced yet */
+    int				wce;
     struct bio_queue_head	queue;		/* head of request queue */
     struct devstat		stats;		/* devstat entry */
     struct disk			disk;		/* disklabel/slice stuff */