[Xen-changelog] Enable multi-word DMA mode 2 for the PIIX3 chipset

[Xen patchbot -unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User adsharma@xxxxxxxxxxxxxxxxxxxx
# Node ID b310a1b71b5460a9a5185b788310701b9a17bbe9
# Parent  75367adf60556a2dfdee6c083c7cb8f3a878237a
Enable multi-word DMA mode 2 for the PIIX3 chipset

Without this patch, Linux PIIX3 driver would see ultra DMA and get confused
and ended up disabling DMA.

With the patch, we're able to see 3x increase in disk read throughput.

Signed-off-by: Winston Wang <winston.l.wang@xxxxxxxxx>
Signed-off-by: Arun Sharma <arun.sharma@xxxxxxxxx>

diff -r 75367adf6055 -r b310a1b71b54 tools/ioemu/hw/ide.c
--- a/tools/ioemu/hw/ide.c      Mon Aug 15 20:50:32 2005
+++ b/tools/ioemu/hw/ide.c      Mon Aug 15 20:50:38 2005
@@ -430,6 +430,7 @@
         put_le16(p + 59, 0x100 | s->mult_sectors);
     put_le16(p + 60, s->nb_sectors);
     put_le16(p + 61, s->nb_sectors >> 16);
+    put_le16(p + 63, 0x07);
     put_le16(p + 80, (1 << 1) | (1 << 2));
     put_le16(p + 82, (1 << 14));
     put_le16(p + 83, (1 << 14));
@@ -460,7 +461,7 @@
     put_le16(p + 48, 1); /* dword I/O (XXX: should not be set on CDROM) */
     put_le16(p + 49, 1 << 9); /* LBA supported, no DMA */
     put_le16(p + 53, 3); /* words 64-70, 54-58 valid */
-    put_le16(p + 63, 0x103); /* DMA modes XXX: may be incorrect */
+    put_le16(p + 63, 0x07); /* Multi-word DMA mode 2 */ 
     put_le16(p + 64, 1); /* PIO modes */
     put_le16(p + 65, 0xb4); /* minimum DMA multiword tx cycle time */
     put_le16(p + 66, 0xb4); /* recommended DMA multiword tx cycle time */

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