mtmd: add --mmproj-device argument (#23255)

* feat: add --mmproj-device arg & backwards compatible MTMD_BACKEND_DEVICE env var

* feat: load mmproj device backend immediately, add -mmdev shortflag

* fix: its a pointer now get the name

* clean up

* gen docs

* nits

---------

Co-authored-by: Xuan Son Nguyen <son@huggingface.co>

tools/mtmd/clip.cpp

@@ -186,14 +186,13 @@ struct clip_ctx {
             throw std::runtime_error("failed to initialize CPU backend");
         }
         if (ctx_params.use_gpu) {
-            auto * backend_name = std::getenv("MTMD_BACKEND_DEVICE");
-            if (backend_name != nullptr) {
-                backend = ggml_backend_init_by_name(backend_name, nullptr);
+            if (ctx_params.device != nullptr) {
+                backend = ggml_backend_dev_init(ctx_params.device, nullptr);
                 if (!backend) {
-                    LOG_WRN("%s: Warning: Failed to initialize \"%s\" backend, falling back to default GPU backend\n", __func__, backend_name);
+                    throw std::runtime_error(string_format("%s: failed to initialize \"%s\" backend\n",
+                                                           __func__, ggml_backend_dev_name(ctx_params.device)));
                 }
-            }
-            if (!backend) {
+            } else {
                 backend = ggml_backend_init_by_type(GGML_BACKEND_DEVICE_TYPE_GPU, nullptr);
                 backend = backend ? backend : ggml_backend_init_by_type(GGML_BACKEND_DEVICE_TYPE_IGPU, nullptr);
             }

tools/mtmd/clip.h

@@ -48,6 +48,7 @@ enum clip_flash_attn_type {
 
 struct clip_context_params {
     bool use_gpu;
+    ggml_backend_dev_t device;
     enum clip_flash_attn_type flash_attn_type;
     int image_min_tokens;
     int image_max_tokens;

tools/mtmd/debug/mtmd-debug.cpp

@@ -84,6 +84,7 @@ int main(int argc, char ** argv) {
         const char * clip_path = params.mmproj.path.c_str();
         mtmd_context_params mparams = mtmd_context_params_default();
         mparams.use_gpu          = params.mmproj_use_gpu;
+        mparams.device           = params.mmproj_device;
         mparams.print_timings    = true;
         mparams.n_threads        = params.cpuparams.n_threads;
         mparams.flash_attn_type  = params.flash_attn_type;

tools/mtmd/mtmd-cli.cpp

@@ -154,6 +154,7 @@ struct mtmd_cli_context {
         const char * clip_path = params.mmproj.path.c_str();
         mtmd_context_params mparams = mtmd_context_params_default();
         mparams.use_gpu          = params.mmproj_use_gpu;
+        mparams.device           = params.mmproj_device;
         mparams.print_timings    = true;
         mparams.n_threads        = params.cpuparams.n_threads;
         mparams.flash_attn_type  = params.flash_attn_type;

tools/mtmd/mtmd.cpp

@@ -456,6 +456,7 @@ static clip_flash_attn_type mtmd_get_clip_flash_attn_type(enum llama_flash_attn_
 mtmd_context_params mtmd_context_params_default() {
     mtmd_context_params params {
         /* use_gpu           */ true,
+        /* device            */ nullptr,
         /* print_timings     */ true,
         /* n_threads         */ 4,
         /* image_marker      */ nullptr,
@@ -564,6 +565,7 @@ struct mtmd_context {
 
         clip_context_params ctx_clip_params {
             /* use_gpu           */ ctx_params.use_gpu,
+            /* device            */ ctx_params.device,
             /* flash_attn_type   */ mtmd_get_clip_flash_attn_type(ctx_params.flash_attn_type),
             /* image_min_tokens  */ ctx_params.image_min_tokens,
             /* image_max_tokens  */ ctx_params.image_max_tokens,

tools/mtmd/mtmd.h

@@ -89,6 +89,7 @@ typedef bool (*mtmd_progress_callback)(float progress, void * user_data);
 
 struct mtmd_context_params {
     bool use_gpu;
+    ggml_backend_dev_t device;
     bool print_timings;
     int n_threads;
     const char * image_marker; // deprecated, use media_marker instead