fix whisper device selection

kcpp_backend.cpp

@@ -70,6 +70,27 @@ ggml_backend_dev_t kcpp_backend_get_device(int index)
     }
 }
 
+ggml_backend_dev_t kcpp_backend_get_gpu_device(int index)
+{
+    if (index < 0) {
+        return get_ggml_main_device();
+    }
+
+    size_t gpu_index = 0;
+    for (size_t i = 0; i < ggml_backend_dev_count(); ++i) {
+        ggml_backend_dev_t dev = ggml_backend_dev_get(i);
+        const enum ggml_backend_dev_type type = ggml_backend_dev_type(dev);
+        if (type == GGML_BACKEND_DEVICE_TYPE_GPU || type == GGML_BACKEND_DEVICE_TYPE_IGPU) {
+            if (gpu_index == (size_t) index) {
+                return dev;
+            }
+            ++gpu_index;
+        }
+    }
+
+    return nullptr;
+}
+
 // this is similar to sd_backend_is, except:
 // - if no backend is provided, checks the first ggml device (should be equivalent to a compile-time check)
 // - tests a |-separated list of backend/device name prefixes

kcpp_backend.h

@@ -20,6 +20,7 @@
 int kcpp_backend_check(const char* name_list, ggml_backend_t backend = nullptr);
 
 ggml_backend_dev_t kcpp_backend_get_device(int index);
+ggml_backend_dev_t kcpp_backend_get_gpu_device(int index);
 
 // per-backend aux functions
 

otherarch/whispercpp/whisper.cpp

@@ -1216,9 +1216,9 @@ static ggml_backend_t whisper_backend_init(const whisper_context_params & params
     ggml_backend_t backend_gpu = NULL;
 
     if (params.use_gpu) {
-        auto device = kcpp_backend_get_device(params.gpu_device);
+        auto device = kcpp_backend_get_gpu_device(params.gpu_device);
         if (!device) {
-            WHISPER_LOG_ERROR("%s: couldn't get device %d\n", __func__, params.gpu_device);
+            WHISPER_LOG_ERROR("%s: couldn't get GPU device %d\n", __func__, params.gpu_device);
         } else {
             WHISPER_LOG_INFO("%s: using backend %s\n", __func__, ggml_backend_dev_name(device));
             backend_gpu = ggml_backend_dev_init(device, nullptr);