v3d: flush jobs reading from transform feedback output buffers

If we are about to write to a transform feedback buffer, we should
make sure that we flush any prior work that intended to read from
any of these buffers.

Fixes piglit test:
spec/ext_transform_feedback/immediate-reuse

Reviewed-by: Eric Anholt <eric@anholt.net>

src/gallium/drivers/v3d/v3dx_draw.c

@@ -179,6 +179,26 @@ v3d_predraw_check_stage_inputs(struct pipe_context *pctx,
         }
 }
 
+static void
+v3d_predraw_check_outputs(struct pipe_context *pctx)
+{
+        struct v3d_context *v3d = v3d_context(pctx);
+
+        /* Flush jobs reading from TF buffers that we are about to write. */
+        if (v3d_transform_feedback_enabled(v3d)) {
+                struct v3d_streamout_stateobj *so = &v3d->streamout;
+
+                for (int i = 0; i < so->num_targets; i++) {
+                        if (!so->targets[i])
+                                continue;
+
+                        const struct pipe_stream_output_target *target =
+                                so->targets[i];
+                        v3d_flush_jobs_reading_resource(v3d, target->buffer);
+                }
+        }
+}
+
 static void
 v3d_emit_gl_shader_state(struct v3d_context *v3d,
                          const struct pipe_draw_info *info)
@@ -509,8 +529,8 @@ v3d_draw_vbo(struct pipe_context *pctx, const struct pipe_draw_info *info)
                 return;
         }
 
-        /* Before setting up the draw, flush anything writing to the textures
-         * that we read from.
+        /* Before setting up the draw, flush anything writing to the resources
+         * that we read from or reading from resources we write to.
          */
         for (int s = 0; s < PIPE_SHADER_COMPUTE; s++)
                 v3d_predraw_check_stage_inputs(pctx, s);
@@ -518,6 +538,8 @@ v3d_draw_vbo(struct pipe_context *pctx, const struct pipe_draw_info *info)
         if (info->indirect)
                 v3d_flush_jobs_writing_resource(v3d, info->indirect->buffer);
 
+        v3d_predraw_check_outputs(pctx);
+
         struct v3d_job *job = v3d_get_job_for_fbo(v3d);
 
         /* If vertex texturing depends on the output of rendering, we need to