drm/gpuvm: Add a helper to check if two VA can be merged

We are going to add flags/properties that will impact the VA merging
ability. Instead of sprinkling tests all over the place in
__drm_gpuvm_sm_map(), let's add a helper aggregating all these checks
can call it for every existing VA we walk through in the
__drm_gpuvm_sm_map() loop.

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Caterina Shablia <caterina.shablia@collabora.com>

Author: Caterina Shablia

drivers/gpu/drm/drm_gpuvm.c

@@ -2172,6 +2172,44 @@ op_unmap_cb(const struct drm_gpuvm_ops *fn, void *priv,
 	return fn->sm_step_unmap(&op, priv);
 }
 
+static bool __can_merge(struct drm_gpuvm *gpuvm, const struct drm_gpuva_op_map *a,
+			const struct drm_gpuva_op_map *b)
+{
+	/* Only GEM-based mappings can be merged, and they must point to
+	 * the same GEM object.
+	 */
+	if (a->gem.obj != b->gem.obj || !a->gem.obj)
+		return false;
+
+	/* Order VAs for the rest of the checks. */
+	if (a->va.addr > b->va.addr)
+		swap(a, b);
+
+	/* We assume the caller already checked that VAs overlap or are
+	 * contiguous.
+	 */
+	if (drm_WARN_ON(gpuvm->drm, b->va.addr > a->va.addr + a->va.range))
+		return false;
+
+	/* We intentionally ignore u64 underflows because all we care about
+	 * here is whether the VA diff matches the GEM offset diff.
+	 */
+	return b->va.addr - a->va.addr == b->gem.offset - a->gem.offset;
+}
+
+static bool can_merge(struct drm_gpuvm *gpuvm, const struct drm_gpuva *a,
+		      const struct drm_gpuva_op_map *b)
+{
+	struct drm_gpuva_op_map tmp = {
+		.va.addr = a->va.addr,
+		.va.range = a->va.range,
+		.gem.offset = a->gem.offset,
+		.gem.obj = a->gem.obj,
+	};
+
+	return __can_merge(gpuvm, &tmp, b);
+}
+
 static int
 __drm_gpuvm_sm_map(struct drm_gpuvm *gpuvm,
 		   const struct drm_gpuvm_ops *ops, void *priv,
@@ -2196,7 +2234,7 @@ __drm_gpuvm_sm_map(struct drm_gpuvm *gpuvm,
 		u64 addr = va->va.addr;
 		u64 range = va->va.range;
 		u64 end = addr + range;
-		bool merge = !!va->gem.obj;
+		bool merge = can_merge(gpuvm, va, &req->map);
 
 		if (madvise && obj)
 			continue;