metal : fix "supports family" call

Author: ggerganov

ggml-metal.h

@@ -98,9 +98,13 @@ GGML_API ggml_backend_t ggml_backend_metal_init(void);
 
 GGML_API bool ggml_backend_is_metal(ggml_backend_t backend);
 
+GGML_API void ggml_backend_metal_set_n_cb(ggml_backend_t backend, int n_cb);
 GGML_API ggml_backend_buffer_type_t ggml_backend_metal_buffer_type(void);
 
-GGML_API void ggml_backend_metal_set_n_cb(ggml_backend_t backend, int n_cb);
+// helper to check if the device supports a specific family
+// ideally, the user code should be doing these checks
+// ref: https://developer.apple.com/metal/Metal-Feature-Set-Tables.pdf
+GGML_API bool ggml_backend_metal_supports_family(ggml_backend_t backend, int family);
 
 #ifdef __cplusplus
 }

ggml-metal.m

@@ -2092,6 +2092,14 @@ void ggml_backend_metal_set_n_cb(ggml_backend_t backend, int n_cb) {
     ggml_metal_set_n_cb(ctx, n_cb);
 }
 
+bool ggml_backend_metal_supports_family(ggml_backend_t backend, int family) {
+    GGML_UNUSED(ggml_backend_is_metal(backend));
+
+    struct ggml_metal_context * ctx = (struct ggml_metal_context *)backend->context;
+
+    return [ctx->device supportsFamily:(MTLGPUFamilyApple1 + family - 1)];
+}
+
 ggml_backend_t ggml_backend_reg_metal_init(const char * params, void * user_data); // silence warning
 
 ggml_backend_t ggml_backend_reg_metal_init(const char * params, void * user_data) {