#13136: Modify create_all_gather_struct to work with linear

ttnn/cpp/ttnn/operations/ccl/all_gather/device/all_gather_op.cpp

@@ -26,14 +26,27 @@ AllGather create_all_gather_struct(
     uint32_t num_devices = devices.size();
 
     uint32_t device_index = 0; // Initialize device index
-    uint32_t receiver_device_id = 0; // Initialize receiver device ID
-    uint32_t sender_device_id = 0; // Initialize sender device ID
+    std::optional<uint32_t> receiver_device_id = std::nullopt; // Initialize receiver device ID
+    std::optional<uint32_t> sender_device_id = std::nullopt; // Initialize sender device ID
 
     for (uint32_t i = 0; i < num_devices; ++i) {
         if (devices[i] == input_tensor.device()) {
             device_index = i;
-            receiver_device_id = devices[(i + 1) % num_devices]->id(); // Next device in the ring
-            sender_device_id = devices[(i + num_devices - 1) % num_devices]->id(); // Previous device in the ring
+            if (topology == ttnn::ccl::Topology::Ring) {
+                // Ring topology
+                receiver_device_id = devices[(i + 1) % num_devices]->id(); // Next device in the ring
+                sender_device_id = devices[(i + num_devices - 1) % num_devices]->id(); // Previous device in the ring
+            } else if (topology == ttnn::ccl::Topology::Linear) {
+                // Linear topology
+                bool is_last_chip_in_clockwise_direction = i == (num_devices - 1);
+                bool is_last_chip_in_counter_clockwise_direction = i == 0;
+                receiver_device_id = is_last_chip_in_clockwise_direction ?
+                    std::nullopt :
+                    std::optional<chip_id_t>(devices.at(i+1)->id());
+                sender_device_id = is_last_chip_in_counter_clockwise_direction ?
+                    std::nullopt :
+                    std::optional<chip_id_t>(devices.at(i-1)->id());
+            }
             break;
         }
     }
@@ -220,7 +233,7 @@ Tensor all_gather(
     const std::optional<size_t> user_defined_num_buffers_per_channel,
     const ttnn::ccl::Topology topology) {
 
-    TT_FATAL(topology != ttnn::ccl::Topology::Linear, "This api currently supported only for Linear topology");
+    TT_FATAL(topology == ttnn::ccl::Topology::Linear, "This api currently supported only for Linear topology");
     const auto mesh_view = mesh_device.get_view();
     std::size_t num_devices = (cluster_axis == 0) ? mesh_view->num_rows() : mesh_view->num_cols();