[Mesa-dev] [PATCH] intel/aubinator: Properly handle batch buffer chaining

[Jason Ekstrand]

The original aubinator that Kristian wrote had a bug in the handling of
MI_BATCH_BUFFER_START that propagated into the version in upstream mesa.
Say you have two batch buffers A and B where A calls MI_BATCH_BUFFER_START
to jump to B.  Now suppose that A and B are placed consecutively in the
address space with A before B.  What can happen is that aubinator will
process A, and start processing B when it should.  When it gets done with
B, it returns and continues to process A.  Because A doesn't have any more
data after the MI_BATCH_BUFFER_START, it will just process a bunch of NOPs
until it gets to the next buffer in memory which is B again.  In this
scenario B gets processed twice which can be very confusing.  If you place
things in memory just right, you can also end up with infinite loops which
are all sorts of fun.

The root problem here is that it continues to process commands even after
an MI_BATCH_BUFFER_START.  By simply checking the 2nd level we can detect
whether or not the command buffer we are jumping to will return here and
stop processing commands if it won't.

Signed-off-by: Jason Ekstrand <jason at jlekstrand.net>
---
 src/intel/tools/aubinator.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/intel/tools/aubinator.c b/src/intel/tools/aubinator.c
index fe1f369..73a7f21 100644
--- a/src/intel/tools/aubinator.c
+++ b/src/intel/tools/aubinator.c
@@ -766,6 +766,13 @@ parse_commands(struct gen_spec *spec, uint32_t *cmds, int size, int engine)
             start = p[1];
 
          parse_commands(spec, gtt + start, 1 << 20, engine);
+
+         /* MI_BATCH_BUFFER_START with "2nd Level Batch Buffer" unset acts
+          * like a goto.  No commands after such a MI_BATCH_BUFFER_START will
+          * get processed so we should bail as well.
+          */
+         if (p[0] & (1 << 22) == 0)
+            break;
       } else if ((p[0] & 0xffff0000) == AUB_MI_BATCH_BUFFER_END) {
          break;
       }
-- 
2.5.0.400.gff86faf