i965: Introduce an UNKNOWN_RING state.

When we first create a batch buffer, it's empty.  We don't actually
know what ring it will be targeted at until the first BEGIN_BATCH or
BEGIN_BATCH_BLT macro.

Previously, one could determine the state of the batch by checking
brw->batch.ring (blit vs. render) and brw->batch.used != 0 (known vs.
unknown).

This should be functionally equivalent, but the tri-state enum is a bit
clearer.

v2: Catch three explicit require_space callers (thanks to Carl and Eric).
v3: Split the boolean -> enum change from the UNKNOWN_RING change.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>

1 files changed, 8 insertions, 3 deletions

diff --git a/src/mesa/drivers/dri/i965/intel_batchbuffer.h b/src/mesa/drivers/dri/i965/intel_batchbuffer.h
index 40b0a29..f7638bc 100644
--- a/src/mesa/drivers/dri/i965/intel_batchbuffer.h
+++ b/src/mesa/drivers/dri/i965/intel_batchbuffer.h
@@ -93,6 +93,7 @@ intel_batchbuffer_emit_dword(struct brw_context *brw, GLuint dword)
    assert(intel_batchbuffer_space(brw) >= 4);
 #endif
    brw->batch.map[brw->batch.used++] = dword;
+   assert(brw->batch.ring != UNKNOWN_RING);
 }
 
 static INLINE void
@@ -106,17 +107,21 @@ intel_batchbuffer_require_space(struct brw_context *brw, GLuint sz,
                                 enum brw_gpu_ring ring)
 {
    /* If we're switching rings, implicitly flush the batch. */
-   if (unlikely(ring != brw->batch.ring) && brw->batch.used && brw->gen >= 6) {
+   if (unlikely(ring != brw->batch.ring) && brw->batch.ring != UNKNOWN_RING &&
+       brw->gen >= 6) {
       intel_batchbuffer_flush(brw);
    }
 
-   brw->batch.ring = ring;
-
 #ifdef DEBUG
    assert(sz < BATCH_SZ - BATCH_RESERVED);
 #endif
    if (intel_batchbuffer_space(brw) < sz)
       intel_batchbuffer_flush(brw);
+
+   /* The intel_batchbuffer_flush() calls above might have changed
+    * brw->batch.ring to UNKNOWN_RING, so we need to set it here at the end.
+    */
+   brw->batch.ring = ring;
 }
 
 static INLINE void