[PATCH v4 08/15] drm/ttm: Use drm_memcpy_from_wc_dbm for TTM bo moves

[Thomas Hellström]

Use fast wc memcpy for reading out of wc memory for TTM bo moves.

Cc: Dave Airlie <airl...@gmail.com>
Cc: Christian König <christian.koe...@amd.com>
Cc: Daniel Vetter <daniel.vet...@ffwll.ch>
Signed-off-by: Thomas Hellström <thomas.hellst...@linux.intel.com>
--
v4:
- Clarify when we try drm_memcpy_from_wc_dbm (Reported by Matthew Auld)
- Be paranoid about when drm_memcpy_from_wc_dbm may fail (Reported by
  Matthew Auld)
---
 drivers/gpu/drm/ttm/ttm_bo_util.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c 
b/drivers/gpu/drm/ttm/ttm_bo_util.c
index 6ac7744a1a5c..ebff603a97f4 100644
--- a/drivers/gpu/drm/ttm/ttm_bo_util.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
@@ -31,6 +31,7 @@
 
 #include <drm/ttm/ttm_bo_driver.h>
 #include <drm/ttm/ttm_placement.h>
+#include <drm/drm_memcpy.h>
 #include <drm/drm_vma_manager.h>
 #include <linux/dma-buf-map.h>
 #include <linux/io.h>
@@ -91,6 +92,7 @@ void ttm_move_memcpy(struct ttm_buffer_object *bo,
        const struct ttm_kmap_iter_ops *src_ops = src_iter->ops;
        struct ttm_tt *ttm = bo->ttm;
        struct dma_buf_map src_map, dst_map;
+       bool wc_memcpy;
        pgoff_t i;
 
        /* Single TTM move. NOP */
@@ -114,11 +116,21 @@ void ttm_move_memcpy(struct ttm_buffer_object *bo,
                return;
        }
 
+       /*
+        * Condition this on src being WC if needed. However i915 perf
+        * selftest indicates that for PAGE_SIZE chunks, wc_memcpy
+        * outperforms memcpy() on all cases except WB->WB where results
+        * are similar.
+        */
+       wc_memcpy = drm_has_memcpy_from_wc();
+
        for (i = 0; i < num_pages; ++i) {
                dst_ops->map_local(dst_iter, &dst_map, i);
                src_ops->map_local(src_iter, &src_map, i);
 
-               if (!src_map.is_iomem && !dst_map.is_iomem) {
+               if (wc_memcpy && drm_memcpy_from_wc_dbm(&dst_map, &src_map, 
PAGE_SIZE)) {
+                       ;
+               } else if (!src_map.is_iomem && !dst_map.is_iomem) {
                        memcpy(dst_map.vaddr, src_map.vaddr, PAGE_SIZE);
                } else if (!src_map.is_iomem) {
                        dma_buf_map_memcpy_to(&dst_map, src_map.vaddr,
-- 
2.31.1