File 0006-e1000-clear-EOP-for-multi-buffer-descripto... of Package xen.3880

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File 0006-e1000-clear-EOP-for-multi-buffer-descriptors.patch of Package xen.3880

From: "Michael S. Tsirkin" <mst@redhat.com>
Date: Tue, 15 Feb 2011 18:27:52 +0200
Subject: e1000: clear EOP for multi-buffer descriptors
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Patch-mainline: v0.15.0-rc0
Git-commit: ee912ccfa007351a62ba42bd60499769f6c02c1e
References: bnc#840196

The e1000 spec says: if software statically allocates
buffers, and uses memory read to check for completed descriptors, it
simply has to zero the status byte in the descriptor to make it ready
for reuse by hardware. This is not a hardware requirement (moving the
hardware tail pointer is), but is necessary for performing an in–memory
scan.

Thus the guest does not have to clear the status byte.  In case it
doesn't we need to clear EOP for all descriptors
except the last.  While I don't know of any such guests,
it's probably a good idea to stick to the spec.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reported-by: Juan Quintela <quintela@redhat.com>
Acked-by: Alex Williamson <alex.williamson@redhat.com>
Acked-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
Acked-by: Michal Kubecek <mkubecek@suse.cz>
---
 tools/qemu-xen-traditional-dir-remote/hw/e1000.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/tools/qemu-xen-traditional-dir-remote/hw/e1000.c b/tools/qemu-xen-traditional-dir-remote/hw/e1000.c
index 34818e0..7e791dc 100644
--- a/tools/qemu-xen-traditional-dir-remote/hw/e1000.c
+++ b/tools/qemu-xen-traditional-dir-remote/hw/e1000.c
@@ -694,11 +694,13 @@ e1000_receive(void *opaque, const uint8_t *buf, int size)
                                           copy_size);
             }
             desc_offset += desc_size;
+            desc.length = cpu_to_le16(desc_size);
             if (desc_offset >= total_size) {
-                desc.length = cpu_to_le16(desc_size);
                 desc.status |= E1000_RXD_STAT_EOP | E1000_RXD_STAT_IXSM;
             } else {
-                desc.length = cpu_to_le16(desc_size);
+                /* Guest zeroing out status is not a hardware requirement.
+                   Clear EOP in case guest didn't do it. */
+                desc.status &= ~E1000_RXD_STAT_EOP;
             }
         } else // as per intel docs; skip descriptors with null buf addr
             DBGOUT(RX, "Null RX descriptor!!\n");
-- 
1.8.1.4

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