[src/trunk]: src/share/man/man4 Document PCIIDE_AMD756_ENABLEDMA and fix a sm...

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

details:   https://anonhg.NetBSD.org/src/rev/fe8a1011e44d
branches:  trunk
changeset: 494450:fe8a1011e44d
user:      bouyer <bouyer%NetBSD.org@localhost>
date:      Thu Jul 06 15:21:33 2000 +0000

description:
Document PCIIDE_AMD756_ENABLEDMA and fix a small typo.

diffstat:

 share/man/man4/pciide.4 |  14 ++++++++++++--
 1 files changed, 12 insertions(+), 2 deletions(-)

diffs (39 lines):

diff -r 9d3b70b963c2 -r fe8a1011e44d share/man/man4/pciide.4
--- a/share/man/man4/pciide.4   Thu Jul 06 15:08:11 2000 +0000
+++ b/share/man/man4/pciide.4   Thu Jul 06 15:21:33 2000 +0000
@@ -1,4 +1,4 @@
-.\"    $NetBSD: pciide.4,v 1.20 2000/06/26 10:12:14 bouyer Exp $
+.\"    $NetBSD: pciide.4,v 1.21 2000/07/06 15:21:33 bouyer Exp $
 .\"
 .\" Copyright (c) 1998 Manuel Bouyer.
 .\"
@@ -39,6 +39,7 @@
 .Cd "pciide* at pci? dev ? function ? flags 0x0000"
 .Cd "pciide* at pnpbios? index ?"
 .Cd "options PCIIDE_CMD064x_DISABLE"
+.Cd "options PCIIDE_AMD756_ENABLEDMA"
 .Sh DESCRIPTION
 The
 .Nm pciide
@@ -85,11 +86,20 @@
 .Sh BUGS
 There's no way to reliably know if a PCI064x controller is enabled or not.
 If the driver finds a PCI064x, it will assume it is enabled unless the
-PCIIDE_CMD064x_DISABLE is specified in the kernel config file.
+PCIIDE_CMD064x_DISABLE option is specified in the kernel config file.
 This will be a problem only if the controller has been disabled in the BIOS
 and another controller has been installed and uses the ISA legacy I/O ports
 and interrupts.
 .Pp
+The AMD756 chip revision D2 has a bug affecting DMA (but not Ultra-DMA)
+modes.  The workaround documented by AMD is to not use DMA on any drive which
+does not support Ultra-DMA modes.  This does not appear to be necessary on all
+drives, the PCIIDE_AMD756_ENABLEDMA option can be used to force multiword DMA
+on the buggy revisions.  Multiword DMA eventually be disabled on a per-drive
+basis with config flags, see
+.Xr wd 4 .
+The bug, if triggered, will cause a total system hang.
+.Pp
 The timings used for the PIO and DMA modes for controllers listed above
 are for a PCI bus running at 30 or 33 Mhz (except the OPTi controller,
 which supports both 25 and 33 Mhz PCI bus timings). This driver may not