[src/trunk]: src/sys/dev/pci Add comment.

[haya <haya%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/711018b58403
branches:  trunk
changeset: 532076:711018b58403
user:      haya <haya%NetBSD.org@localhost>
date:      Fri May 31 09:54:52 2002 +0000

description:
Add comment.

diffstat:

 sys/dev/pci/pccbb.c |  15 +++++++++++++--
 1 files changed, 13 insertions(+), 2 deletions(-)

diffs (36 lines):

diff -r 4091349de284 -r 711018b58403 sys/dev/pci/pccbb.c
--- a/sys/dev/pci/pccbb.c       Fri May 31 09:45:44 2002 +0000
+++ b/sys/dev/pci/pccbb.c       Fri May 31 09:54:52 2002 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: pccbb.c,v 1.75 2002/03/05 11:56:33 haya Exp $  */
+/*     $NetBSD: pccbb.c,v 1.76 2002/05/31 09:54:52 haya Exp $  */
 
 /*
  * Copyright (c) 1998, 1999 and 2000
@@ -31,7 +31,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: pccbb.c,v 1.75 2002/03/05 11:56:33 haya Exp $");
+__KERNEL_RCSID(0, "$NetBSD: pccbb.c,v 1.76 2002/05/31 09:54:52 haya Exp $");
 
 /*
 #define CBB_DEBUG
@@ -2969,6 +2969,17 @@
                if (align < 16) {
                        return 1;
                }
+               /*
+                * XXX: align more than 0x1000 to avoid overwrapping
+                * memory windows for two or more devices.  0x1000
+                * means memory window's granularity.
+                *
+                * Two or more devices should be able to share same
+                * memory window region.  However, overrapping memory
+                * window is not good because some devices, such as
+                * 3Com 3C575[BC], have a broken address decoder and
+                * intrude other's memory region.
+                */
                if (align < 0x1000) {
                        align = 0x1000;
                }