From: Alan Cox <alan@lxorguk.ukuu.org.uk>

Matthew Wilcox asked that this got a comment explaining why it is done so
here it is.

Signed-off-by: Alan Cox <alan@redhat.com>
Cc: Bartlomiej Zolnierkiewicz <B.Zolnierkiewicz@elka.pw.edu.pl>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

 include/asm-i386/ide.h |    6 ++++++
 1 files changed, 6 insertions(+)

diff -puN include/asm-i386/ide.h~ide-explain-the-pci-bus-test include/asm-i386/ide.h
--- devel/include/asm-i386/ide.h~ide-explain-the-pci-bus-test	2005-10-23 13:15:21.000000000 -0700
+++ devel-akpm/include/asm-i386/ide.h	2005-10-23 13:15:21.000000000 -0700
@@ -41,6 +41,12 @@ static __inline__ int ide_default_irq(un
 
 static __inline__ unsigned long ide_default_io_base(int index)
 {
+	/*
+	 *	If PCI is present then it is not safe to poke around
+	 *	the other legacy IDE ports. Only 0x1f0 and 0x170 are
+	 *	defined compatibility mode ports for PCI. A user can
+	 *	override this using ide= but we must default safe.
+	 */
 	if (pci_find_device(PCI_ANY_ID, PCI_ANY_ID, NULL) == NULL) {
 		switch(index) {
 			case 2: return 0x1e8;
_