[PATCH 4/6] drm/nouveau: introduce NOUVEAU_GEM_TILE_WCUS

[Lucas Stach]

This flag allows userspace to give the kernel a hint that it should use
a non-snooped resource. To guarantee coherency at all times mappings
into userspace are done write combined, so userspace should avoid
reading back from those resources.

Signed-off-by: Lucas Stach <dev at lynxeye.de>
---
On x86 an optimized userspace can save up on snoop traffic in the
system, on ARM the benefits are potentially much larger, as we can save
the manual cache flush/invalidate.
---
 drivers/gpu/drm/nouveau/nouveau_bo.c | 11 ++++++++++-
 drivers/gpu/drm/nouveau/nouveau_bo.h |  1 +
 include/uapi/drm/nouveau_drm.h       |  1 +
 3 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.c 
b/drivers/gpu/drm/nouveau/nouveau_bo.c
index f4a2eb9..c5fcbcc 100644
--- a/drivers/gpu/drm/nouveau/nouveau_bo.c
+++ b/drivers/gpu/drm/nouveau/nouveau_bo.c
@@ -231,6 +231,12 @@ nouveau_bo_new(struct drm_device *dev, int size, int align,

        nouveau_bo_fixup_align(nvbo, flags, &align, &size);
        nvbo->bo.mem.num_pages = size >> PAGE_SHIFT;
+
+       if (tile_flags & NOUVEAU_GEM_TILE_WCUS)
+               nvbo->valid_caching = TTM_PL_FLAG_UNCACHED | TTM_PL_FLAG_WC;
+       else
+               nvbo->valid_caching = TTM_PL_MASK_CACHING;
+
        nouveau_bo_placement_set(nvbo, flags, 0);

        acc_size = ttm_bo_dma_acc_size(&drm->ttm.bdev, size,
@@ -292,7 +298,7 @@ void
 nouveau_bo_placement_set(struct nouveau_bo *nvbo, uint32_t type, uint32_t busy)
 {
        struct ttm_placement *pl = &nvbo->placement;
-       uint32_t flags = TTM_PL_MASK_CACHING |
+       uint32_t flags = nvbo->valid_caching |
                (nvbo->pin_refcnt ? TTM_PL_FLAG_NO_EVICT : 0);

        pl->placement = nvbo->placements;
@@ -1554,6 +1560,9 @@ nouveau_bo_vma_add(struct nouveau_bo *nvbo, struct 
nouveau_vm *vm,
        if (nvbo->bo.mem.mem_type == TTM_PL_VRAM)
                nouveau_vm_map(vma, nvbo->bo.mem.mm_node);
        else if (nvbo->bo.mem.mem_type == TTM_PL_TT) {
+               if (!(nvbo->valid_caching & TTM_PL_FLAG_CACHED))
+                       vma->access |= NV_MEM_ACCESS_NOSNOOP;
+
                if (node->sg)
                        nouveau_vm_map_sg_table(vma, 0, size, node);
                else
diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.h 
b/drivers/gpu/drm/nouveau/nouveau_bo.h
index 653dbbb..2ecf8b7 100644
--- a/drivers/gpu/drm/nouveau/nouveau_bo.h
+++ b/drivers/gpu/drm/nouveau/nouveau_bo.h
@@ -9,6 +9,7 @@ struct nouveau_bo {
        struct ttm_buffer_object bo;
        struct ttm_placement placement;
        u32 valid_domains;
+       u32 valid_caching;
        u32 placements[3];
        u32 busy_placements[3];
        struct ttm_bo_kmap_obj kmap;
diff --git a/include/uapi/drm/nouveau_drm.h b/include/uapi/drm/nouveau_drm.h
index 2a5769f..4948eee2 100644
--- a/include/uapi/drm/nouveau_drm.h
+++ b/include/uapi/drm/nouveau_drm.h
@@ -36,6 +36,7 @@
 #define NOUVEAU_GEM_TILE_32BPP       0x00000002
 #define NOUVEAU_GEM_TILE_ZETA        0x00000004
 #define NOUVEAU_GEM_TILE_NONCONTIG   0x00000008
+#define NOUVEAU_GEM_TILE_WCUS        0x00000010 /* write-combined, unsnooped */

 struct drm_nouveau_gem_info {
        uint32_t handle;
-- 
1.8.3.1