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-rw-r--r--include/drm/ttm/ttm_placement.h11
1 files changed, 11 insertions, 0 deletions
diff --git a/include/drm/ttm/ttm_placement.h b/include/drm/ttm/ttm_placement.h
index 76d1b9119a2b..8074d0f6cae5 100644
--- a/include/drm/ttm/ttm_placement.h
+++ b/include/drm/ttm/ttm_placement.h
@@ -35,6 +35,17 @@
/*
* Memory regions for data placement.
+ *
+ * Buffers placed in TTM_PL_SYSTEM are considered under TTMs control and can
+ * be swapped out whenever TTMs thinks it is a good idea.
+ * In cases where drivers would like to use TTM_PL_SYSTEM as a valid
+ * placement they need to be able to handle the issues that arise due to the
+ * above manually.
+ *
+ * For BO's which reside in system memory but for which the accelerator
+ * requires direct access (i.e. their usage needs to be synchronized
+ * between the CPU and accelerator via fences) a new, driver private
+ * placement that can handle such scenarios is a good idea.
*/
#define TTM_PL_SYSTEM 0