x.__dlpack_device__() returns ID of the parent device

dpctl/_sycl_platform.pyx

@@ -267,14 +267,20 @@ cdef class SyclPlatform(_SyclPlatform):
         """Returns the default platform context for this platform
 
         Returns:
-            SyclContext: The default context for the platform.
+            SyclContext
+                The default context for the platform.
+        Raises:
+            SyclContextCreationError
+                If default_context is not supported
         """
         cdef DPCTLSyclContextRef CRef = (
             DPCTLPlatform_GetDefaultContext(self._platform_ref)
         )
 
         if (CRef == NULL):
-            raise RuntimeError("Getting default error ran into a problem")
+            raise SyclContextCreationError(
+                "Getting default_context ran into a problem"
+            )
         else:
             return SyclContext._create(CRef)
 

dpctl/tensor/_dlpack.pxd

@@ -18,6 +18,7 @@
 # cython: language_level=3
 # cython: linetrace=True
 
+from .._sycl_device cimport SyclDevice
 from ._usmarray cimport usm_ndarray
 
 
@@ -32,6 +33,8 @@ cpdef usm_ndarray from_dlpack_capsule(object dltensor) except +
 
 cpdef from_dlpack(array)
 
+cdef int get_parent_device_ordinal_id(SyclDevice dev) except *
+
 cdef class DLPackCreationError(Exception):
     """
     A DLPackCreateError exception is raised when constructing

dpctl/tensor/_dlpack.pyx

@@ -121,6 +121,39 @@ cdef void _managed_tensor_deleter(DLManagedTensor *dlm_tensor) noexcept with gil
         dlm_tensor.manager_ctx = NULL
         stdlib.free(dlm_tensor)
 
+cdef object _get_default_context(c_dpctl.SyclDevice dev) except *:
+    try:
+        if _IS_LINUX:
+            default_context = dev.sycl_platform.default_context
+        else:
+            default_context = None
+    except RuntimeError:
+        # RT does not support default_context, e.g. Windows
+        default_context = None
+
+    return default_context
+
+
+cdef int get_parent_device_ordinal_id(c_dpctl.SyclDevice dev) except *:
+    cdef DPCTLSyclDeviceRef pDRef = NULL
+    cdef DPCTLSyclDeviceRef tDRef = NULL
+    cdef c_dpctl.SyclDevice p_dev
+
+    pDRef = DPCTLDevice_GetParentDevice(dev.get_device_ref())
+    if pDRef is not NULL:
+        # if dev is a sub-device, find its parent
+        # and return its overall ordinal id
+        tDRef = DPCTLDevice_GetParentDevice(pDRef)
+        while tDRef is not NULL:
+            DPCTLDevice_Delete(pDRef)
+            pDRef = tDRef
+            tDRef = DPCTLDevice_GetParentDevice(pDRef)
+        p_dev = c_dpctl.SyclDevice._create(pDRef)
+        return p_dev.get_overall_ordinal()
+
+    # return overall ordinal id of argument device
+    return dev.get_overall_ordinal()
+
 
 cpdef to_dlpack_capsule(usm_ndarray usm_ary):
     """
@@ -168,14 +201,7 @@ cpdef to_dlpack_capsule(usm_ndarray usm_ary):
     ary_sycl_queue = usm_ary.get_sycl_queue()
     ary_sycl_device = ary_sycl_queue.get_sycl_device()
 
-    try:
-        if _IS_LINUX:
-            default_context = ary_sycl_device.sycl_platform.default_context
-        else:
-            default_context = None
-    except RuntimeError:
-        # RT does not support default_context, e.g. Windows
-        default_context = None
+    default_context = _get_default_context(ary_sycl_device)
     if default_context is None:
         # check that ary_sycl_device is a non-partitioned device
         pDRef = DPCTLDevice_GetParentDevice(ary_sycl_device.get_device_ref())

dpctl/tensor/_usmarray.pyx

@@ -954,10 +954,10 @@ cdef class usm_ndarray:
             DLPackCreationError: when array is allocation on a partitioned
                 SYCL device
         """
-        cdef int dev_id = (<c_dpctl.SyclDevice>self.sycl_device).get_overall_ordinal()
+        cdef int dev_id = c_dlpack.get_parent_device_ordinal_id(<c_dpctl.SyclDevice>self.sycl_device)
         if dev_id < 0:
             raise c_dlpack.DLPackCreationError(
-                "DLPack protocol is only supported for non-partitioned devices"
+                "Could not determine id of the device where array was allocated."
             )
         else:
             return (

dpctl/tests/test_usm_ndarray_dlpack.py

@@ -197,3 +197,39 @@ def test_from_dlpack_fortran_contig_array_roundtripping():
 
     assert dpt.all(dpt.equal(ar2d_f, ar2d_r))
     assert dpt.all(dpt.equal(ar2d_c, ar2d_r))
+
+
+def test_dlpack_from_subdevice():
+    """
+    This test checks that array allocated on a sub-device,
+    with memory bound to platform-default SyclContext can be
+    exported and imported via DLPack.
+    """
+    n = 64
+    try:
+        dev = dpctl.SyclDevice()
+    except dpctl.SyclDeviceCreationError:
+        pytest.skip("No default device available")
+    try:
+        sdevs = dev.create_sub_devices(partition="next_partitionable")
+    except dpctl.SyclSubDeviceCreationError:
+        sdevs = None
+    try:
+        sdevs = (
+            dev.create_sub_devices(partition=[1, 1]) if sdevs is None else sdevs
+        )
+    except dpctl.SyclSubDeviceCreationError:
+        pytest.skip("Default device can not be partitioned")
+    assert isinstance(sdevs, list) and len(sdevs) > 0
+    try:
+        ctx = sdevs[0].sycl_platform.default_context
+    except dpctl.SyclContextCreationError:
+        pytest.skip("Platform's default_context is not available")
+    try:
+        q = dpctl.SyclQueue(ctx, sdevs[0])
+    except dpctl.SyclQueueCreationError:
+        pytest.skip("Queue could not be created")
+
+    ar = dpt.arange(n, dtype=dpt.int32, sycl_queue=q)
+    ar2 = dpt.from_dlpack(ar)
+    assert ar2.sycl_device == sdevs[0]

libsyclinterface/source/dpctl_sycl_platform_interface.cpp

@@ -225,8 +225,17 @@ DPCTLPlatform_GetDefaultContext(__dpctl_keep const DPCTLSyclPlatformRef PRef)
 {
     auto P = unwrap<platform>(PRef);
     if (P) {
-        const auto &default_ctx = P->ext_oneapi_get_default_context();
-        return wrap<context>(new context(default_ctx));
+#ifdef SYCL_EXT_ONEAPI_DEFAULT_CONTEXT
+        try {
+            const auto &default_ctx = P->ext_oneapi_get_default_context();
+            return wrap<context>(new context(default_ctx));
+        } catch (const std::exception &ex) {
+            error_handler(ex, __FILE__, __func__, __LINE__);
+            return nullptr;
+        }
+#else
+        return nullptr;
+#endif
     }
     else {
         error_handler(