rebase

mlx/CMakeLists.txt

@@ -55,6 +55,9 @@ endif()
 
 if(MLX_BUILD_CUDA)
   add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/backend/cuda)
+else()
+  target_sources(mlx
+                 PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/backend/cuda/no_cuda.cpp)
 endif()
 
 if(MLX_BUILD_METAL OR MLX_BUILD_CUDA)

mlx/backend/cuda/CMakeLists.txt

@@ -12,6 +12,7 @@ target_sources(
           ${CMAKE_CURRENT_SOURCE_DIR}/copy/copy_general.cu
           ${CMAKE_CURRENT_SOURCE_DIR}/copy/copy_general_dynamic.cu
           ${CMAKE_CURRENT_SOURCE_DIR}/copy/copy_general_input.cu
+          ${CMAKE_CURRENT_SOURCE_DIR}/cuda.cpp
           ${CMAKE_CURRENT_SOURCE_DIR}/device.cpp
           ${CMAKE_CURRENT_SOURCE_DIR}/eval.cpp
           ${CMAKE_CURRENT_SOURCE_DIR}/event.cu

mlx/backend/cuda/cuda.cpp

@@ -0,0 +1,11 @@
+// Copyright © 2025 Apple Inc.
+
+#include "mlx/backend/cuda/cuda.h"
+
+namespace mlx::core::cu {
+
+bool is_available() {
+  return true;
+}
+
+} // namespace mlx::core::cu

mlx/backend/cuda/cuda.h

@@ -0,0 +1,10 @@
+// Copyright © 2025 Apple Inc.
+
+#pragma once
+
+namespace mlx::core::cu {
+
+/* Check if the CUDA backend is available. */
+bool is_available();
+
+} // namespace mlx::core::cu

mlx/backend/cuda/no_cuda.cpp

@@ -0,0 +1,11 @@
+// Copyright © 2025 Apple Inc.
+
+#include "mlx/backend/cuda/cuda.h"
+
+namespace mlx::core::cu {
+
+bool is_available() {
+  return false;
+}
+
+} // namespace mlx::core::cu

mlx/mlx.h

@@ -3,6 +3,7 @@
 #pragma once
 
 #include "mlx/array.h"
+#include "mlx/backend/cuda/cuda.h"
 #include "mlx/backend/metal/metal.h"
 #include "mlx/compile.h"
 #include "mlx/device.h"

python/src/array.cpp

@@ -17,10 +17,7 @@
 #include "python/src/indexing.h"
 #include "python/src/utils.h"
 
-#include "mlx/device.h"
+#include "mlx/mlx.h"
-#include "mlx/ops.h"
-#include "mlx/transforms.h"
-#include "mlx/utils.h"
 
 namespace mx = mlx::core;
 namespace nb = nanobind;
@@ -461,9 +458,12 @@ void init_array(nb::module_& m) {
       .def(
           "__dlpack_device__",
           [](const mx::array& a) {
+            // See
+            // https://github.com/dmlc/dlpack/blob/5c210da409e7f1e51ddf445134a4376fdbd70d7d/include/dlpack/dlpack.h#L74
             if (mx::metal::is_available()) {
-              // Metal device is available
               return nb::make_tuple(8, 0);
+            } else if (mx::cu::is_available()) {
+              return nb::make_tuple(13, 0);
             } else {
               // CPU device
               return nb::make_tuple(1, 0);

python/src/device.cpp

@@ -58,4 +58,9 @@ void init_device(nb::module_& m) {
       &mx::set_default_device,
       "device"_a,
       R"pbdoc(Set the default device.)pbdoc");
+  m.def(
+      "is_available",
+      &mx::is_available,
+      "device"_a,
+      R"pbdoc(Check if a back-end is available for the given device.)pbdoc");
 }