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

[Ben Skeggs]

On Wed, Aug 28, 2013 at 10:00 AM, Lucas Stach <dev at lynxeye.de> wrote:
> 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.
Do any other combinations of cached/uncached and snooped/non-snooped
make any sense?  If so, perhaps we want to split the flags.

>
> 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
>