__dlpack_device__() returns ID of the parent device

It gives ID (position in `sycl::device::get_devices()`) for the
root device that the array allocation device descends from for
sub-devices, or ID of the allocation device is that device is a
root device.

Author: oleksandr-pavlyk

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 (