From 6a740c4a4f52ac5aa8a0f35e828d20d0bf0692a8 Mon Sep 17 00:00:00 2001
From: Alexander Motin <mav@FreeBSD.org>
Date: Mon, 25 Mar 2013 13:58:17 +0000
Subject: [PATCH] Read Asynchronous Notification statuses only if Port
 Multiplier or ATAPI device are connected. ATA disks are not using ANs, while
 the extra register read operation is quite expensive.

---
 sys/dev/ahci/ahci.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/sys/dev/ahci/ahci.c b/sys/dev/ahci/ahci.c
index c39f9741b1ff..f7dba1ebc33f 100644
--- a/sys/dev/ahci/ahci.c
+++ b/sys/dev/ahci/ahci.c
@@ -1466,7 +1466,8 @@ ahci_ch_intr(void *data)
 	if (ch->numrslots != ch->numtslots)
 		cstatus |= ATA_INL(ch->r_mem, AHCI_P_CI);
 	/* Read SNTF in one of possible ways. */
-	if (istatus & AHCI_P_IX_SDB) {
+	if ((istatus & AHCI_P_IX_SDB) &&
+	    (ch->pm_present || ch->curr[0].atapi != 0)) {
 		if (ch->caps & AHCI_CAP_SSNTF)
 			sntf = ATA_INL(ch->r_mem, AHCI_P_SNTF);
 		else if (ch->fbs_enabled) {