make RAM device optional

Having a RAM device does not make sense for chips like GK20A which have
no dedicated video memory. The dummy RAM device that we used so far
works as a temporary band-aid, but in the longer term it is desirable
for the driver to be able to work without any kind of VRAM.

This patch adds a few conditionals in places where a RAM device was
assumed to be present and allows some more objects to be allocated from
the TT domain, allowing Nouveau to handle GPUs for which
pfb->ram == NULL.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

1 files changed, 11 insertions, 3 deletions

diff --git a/drivers/gpu/drm/nouveau/nv84_fence.c b/drivers/gpu/drm/nouveau/nv84_fence.c
index bf429cabbaa8..a03db4368696 100644
--- a/drivers/gpu/drm/nouveau/nv84_fence.c
+++ b/drivers/gpu/drm/nouveau/nv84_fence.c
@@ -215,6 +215,7 @@ nv84_fence_create(struct nouveau_drm *drm)
 {
         struct nvkm_fifo *pfifo = nvxx_fifo(&drm->device);
         struct nv84_fence_priv *priv;
+        u32 domain;
         int ret;
 
         priv = drm->fence = kzalloc(sizeof(*priv), GFP_KERNEL);
@@ -231,10 +232,17 @@ nv84_fence_create(struct nouveau_drm *drm)
         priv->base.context_base = fence_context_alloc(priv->base.contexts);
         priv->base.uevent = true;
 
-        ret = nouveau_bo_new(drm->dev, 16 * priv->base.contexts, 0,
-                             TTM_PL_FLAG_VRAM, 0, 0, NULL, NULL, &priv->bo);
+        /* Use VRAM if there is any ; otherwise fallback to system memory */
+        domain = drm->device.info.ram_size != 0 ? TTM_PL_FLAG_VRAM :
+                         /*
+                          * fences created in sysmem must be non-cached or we
+                          * will lose CPU/GPU coherency!
+                          */
+                         TTM_PL_FLAG_TT | TTM_PL_FLAG_UNCACHED;
+        ret = nouveau_bo_new(drm->dev, 16 * priv->base.contexts, 0, domain, 0,
+                             0, NULL, NULL, &priv->bo);
         if (ret == 0) {
-                ret = nouveau_bo_pin(priv->bo, TTM_PL_FLAG_VRAM, false);
+                ret = nouveau_bo_pin(priv->bo, domain, false);
                 if (ret == 0) {
                         ret = nouveau_bo_map(priv->bo);
                         if (ret)