Using CPU maps of non-coherent buffers can get us in a lot of trouble,
and WC maps are a reasonable alternative anyway. Guard against shooting
ourselves in the foot by adding an assert, and comment.
---
src/mesa/drivers/dri/i965/brw_bufmgr.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/src/mesa/drivers/dri/i965/brw_bufmgr.c
b/src/mesa/drivers/dri/i965/brw_bufmgr.c
index 74ed543eece..da50650d022 100644
--- a/src/mesa/drivers/dri/i965/brw_bufmgr.c
+++ b/src/mesa/drivers/dri/i965/brw_bufmgr.c
@@ -669,6 +669,12 @@ brw_bo_map_cpu(struct brw_context *brw, struct brw_bo *bo,
unsigned flags)
{
struct brw_bufmgr *bufmgr = bo->bufmgr;
+ /* We disallow CPU maps for writing to non-coherent buffers, as the
+ * CPU map can become invalidated when a batch is flushed out, which
+ * can happen at unpredictable times. You should use WC maps instead.
+ */
+ assert(bo->cache_coherent || !(flags & MAP_WRITE));
+
if (!bo->map_cpu) {
struct drm_i915_gem_mmap mmap_arg;
void *map;
--
2.13.2
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