intel: Add an interface for saving/restoring the batchbuffer state.

This will be used to avoid the prepare() step in the i965 driver's
state setup.  Instead, we can just speculatively emit the primitive
into the batchbuffer, then check if the batch is too big, rollback and
flush, and replay the primitive.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Acked-by: Paul Berry <stereotype441@gmail.com>

configure.ac

@@ -24,7 +24,7 @@ USER_CXXFLAGS="$CXXFLAGS"
 dnl Versions for external dependencies
 LIBDRM_REQUIRED=2.4.24
 LIBDRM_RADEON_REQUIRED=2.4.24
-LIBDRM_INTEL_REQUIRED=2.4.24
+LIBDRM_INTEL_REQUIRED=2.4.27
 LIBDRM_NOUVEAU_REQUIRED=0.6
 DRI2PROTO_REQUIRED=2.6
 GLPROTO_REQUIRED=1.4.14

src/mesa/drivers/dri/intel/intel_batchbuffer.c

@@ -87,6 +87,27 @@ intel_batchbuffer_reset(struct intel_context *intel)
    intel->batch.used = 0;
 }
 
+void
+intel_batchbuffer_save_state(struct intel_context *intel)
+{
+   intel->batch.saved.used = intel->batch.used;
+   intel->batch.saved.reloc_count =
+      drm_intel_gem_bo_get_reloc_count(intel->batch.bo);
+}
+
+void
+intel_batchbuffer_reset_to_saved(struct intel_context *intel)
+{
+   drm_intel_gem_bo_clear_relocs(intel->batch.bo, intel->batch.saved.reloc_count);
+
+   intel->batch.used = intel->batch.saved.used;
+
+   /* Cached batch state is dead, since we just cleared some unknown part of the
+    * batchbuffer.  Assume that the caller resets any other state necessary.
+    */
+   clear_cache(intel);
+}
+
 void
 intel_batchbuffer_free(struct intel_context *intel)
 {

src/mesa/drivers/dri/intel/intel_batchbuffer.h

@@ -12,6 +12,8 @@
 void intel_batchbuffer_init(struct intel_context *intel);
 void intel_batchbuffer_reset(struct intel_context *intel);
 void intel_batchbuffer_free(struct intel_context *intel);
+void intel_batchbuffer_save_state(struct intel_context *intel);
+void intel_batchbuffer_reset_to_saved(struct intel_context *intel);
 
 void _intel_batchbuffer_flush(struct intel_context *intel,
 			      const char *file, int line);

src/mesa/drivers/dri/intel/intel_context.h

@@ -210,6 +210,11 @@ struct intel_context
 
       uint32_t state_batch_offset;
       bool is_blit;
+
+      struct {
+	 uint16_t used;
+	 int reloc_count;
+      } saved;
    } batch;
 
    drm_intel_bo *first_post_swapbuffers_batch;