ggml-webgpu: Check earlier for WebGPU required features (ggml-org#23879)

Author: reeselevine

ggml/src/ggml-webgpu/ggml-webgpu.cpp

@@ -3724,7 +3724,7 @@ static void ggml_webgpu_init_memset_pipeline(webgpu_global_context & ctx) {
     ctx->memset_pipeline = ggml_webgpu_create_pipeline(ctx->device, wgsl_memset, "memset", constants);
 }
 
-static bool create_webgpu_device(ggml_backend_webgpu_reg_context * ctx) {
+static void create_webgpu_device(ggml_backend_webgpu_reg_context * ctx) {
     wgpu::RequestAdapterOptions options = {};
 
 #ifndef __EMSCRIPTEN__
@@ -3762,10 +3762,6 @@ static bool create_webgpu_device(ggml_backend_webgpu_reg_context * ctx) {
     ctx->webgpu_global_ctx->command_submit_batch_size = ggml_backend_webgpu_get_command_submit_batch_size();
     ctx->webgpu_global_ctx->max_inflight_batches      = ggml_backend_webgpu_get_max_inflight_batches();
     ctx->webgpu_global_ctx->vendor                    = info.vendor;
-    wgpu::SupportedFeatures features;
-    ctx->webgpu_global_ctx->adapter.GetFeatures(&features);
-    // we require f16 support
-    GGML_ASSERT(ctx->webgpu_global_ctx->adapter.HasFeature(wgpu::FeatureName::ShaderF16));
     ctx->webgpu_global_ctx->capabilities.supports_subgroups =
         ctx->webgpu_global_ctx->adapter.HasFeature(wgpu::FeatureName::Subgroups);
     // for dot4I8packed
@@ -3877,7 +3873,6 @@ static bool create_webgpu_device(ggml_backend_webgpu_reg_context * ctx) {
         "device_desc: %s\n",
         info.vendorID, std::string(info.vendor).c_str(), std::string(info.architecture).c_str(), info.deviceID,
         std::string(info.device).c_str(), std::string(info.description).c_str());
-    return true;
 }
 
 static webgpu_context initialize_webgpu_context(ggml_backend_dev_t dev) {
@@ -4507,16 +4502,24 @@ ggml_backend_reg_t ggml_backend_webgpu_reg() {
             UINT64_MAX);
     }
 
-    if (adapter != nullptr) {
+    // WebGPU backend requires f16 support and, on native, implicit device synchronization.
+    if (adapter != nullptr && adapter.HasFeature(wgpu::FeatureName::ShaderF16)
+#ifndef __EMSCRIPTEN__
+        && adapter.HasFeature(wgpu::FeatureName::ImplicitDeviceSynchronization)
+#endif
+    ) {
         ctx->device_count = 1;
     }
 
     return ®
 }
 
 ggml_backend_t ggml_backend_webgpu_init(void) {
-    ggml_backend_dev_t dev = ggml_backend_reg_dev_get(ggml_backend_webgpu_reg(), 0);
-
+    ggml_backend_reg_t reg = ggml_backend_webgpu_reg();
+    if (ggml_backend_reg_dev_count(reg) == 0) {
+        return nullptr;
+    }
+    ggml_backend_dev_t dev = ggml_backend_reg_dev_get(reg, 0);
     return ggml_backend_webgpu_backend_init(dev, nullptr);
 }