[Xen-iommu PATCH] Fix Phase Mismatch Jump handling

[Michal Novotny <minovotn@redhat.com>]

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Hi,
this is the patch written by Paolo Bonzini to make Windows x64 guests 
working fine with SCSI using the LSI SCSI controller. There was a buggy 
implementation of Phase Mismatch handling in QEMU and this is the patch 
that Paolo sent to upstream QEMU and it seems to be working fine with 
Win64 drivers.

Michal

-- 
Michal Novotny<minovotn@redhat.com>, RHCE
Virtualization Team (xen userspace), Red Hat


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lsi_bad_phase has a bug in the choice of pmjad1/pmjad2.  This does
not matter with Linux guests because it uses just one routine for
both, but it breaks Windows 64-bit guests.  This is the text
from the spec:

   "[The PMJCTL] bit controls which decision mechanism is used
   when jumping on phase mismatch. When this bit is cleared the
   LSI53C895A will use Phase Mismatch Jump Address 1 (PMJAD1) when
   the WSR bit is cleared and Phase Mismatch Jump Address 2 (PMJAD2)
   when the WSR bit is set.  When this bit is set the LSI53C895A will
   use jump address one (PMJAD1) on data out (data out, command,
   message out) transfers and jump address two (PMJAD2) on data in
   (data in, status, message in) transfers."

Which means:

    CCNTL0.PMJCTL
        0              SCNTL2.WSR = 0             PMJAD1
        0              SCNTL2.WSR = 1             PMJAD2
        1                    out                  PMJAD1
        1                    in                   PMJAD2

In qemu, what you get instead is:

    CCNTL0.PMJCTL
        0                    out                  PMJAD1
        0                    in                   PMJAD2    <<<<<
        1                    out                  PMJAD1
        1                    in                   PMJAD1    <<<<<

Considering that qemu always has SCNTL2.WSR cleared, the two marked cases
(corresponding to phase mismatch on input) are always jumping to the
wrong PMJAD register.  The patch implements the correct semantics.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 hw/lsi53c895a.c |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/hw/lsi53c895a.c b/hw/lsi53c895a.c
index 5a47276..a4db51d 100644
--- a/hw/lsi53c895a.c
+++ b/hw/lsi53c895a.c
@@ -433,11 +433,14 @@ static void lsi_bad_phase(LSIState *s, int out, int new_phase)
 {
     /* Trigger a phase mismatch.  */
     if (s->ccntl0 & LSI_CCNTL0_ENPMJ) {
-        if ((s->ccntl0 & LSI_CCNTL0_PMJCTL) || out) {
-            s->dsp = s->pmjad1;
+        int dest;
+        if ((s->ccntl0 & LSI_CCNTL0_PMJCTL)) {
+            dest = out ? 1 : 2;
         } else {
-            s->dsp = s->pmjad2;
+            dest = (s->scntl2 & LSI_SCNTL2_WSR ? 2 : 1);
         }
+
+        s->dsp = (dest == 1) ? s->pmjad1 : s->pmjad2;
         DPRINTF("Data phase mismatch jump to %08x\n", s->dsp);
     } else {
         DPRINTF("Phase mismatch interrupt\n");
-- 
1.5.5.6


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