Fix crash when Llama-based text encoder KV cache init runs on CPU

init_kv_cache probed comfy_kitchen.flash_attention_decode_is_available()
unconditionally, which calls torch.cuda.get_device_capability() and raises
ValueError when the execution device is CPU (e.g. MiniMax Music3 text
encoder offloaded to CPU on low-VRAM GPUs). Guard the probe with
comfy.model_management.is_device_cuda(), matching the pattern already
used elsewhere in this file (ar.py's cuda_device check).

Fixes #15607

comfy/text_encoders/llama.py

@@ -791,7 +791,7 @@ class Llama2_(nn.Module):
 
     def init_kv_cache(self, batch, capacity, device, dtype):
         caches = []
-        fixed_kv = self.fixed_kv and comfy_kitchen.flash_attention_decode_is_available(device)
+        fixed_kv = self.fixed_kv and comfy.model_management.is_device_cuda(device) and comfy_kitchen.flash_attention_decode_is_available(device)
         for _ in range(self.config.num_hidden_layers):
             if fixed_kv:
                 key = torch.empty((batch, capacity, self.config.num_key_value_heads, self.config.head_dim), device=device, dtype=dtype)

tests-unit/comfy_test/test_llama_init_kv_cache.py

@@ -0,0 +1,39 @@
+"""Regression test for init_kv_cache crashing when the text encoder runs on CPU."""
+
+from __future__ import annotations
+
+import torch
+
+from comfy.cli_args import args
+
+if not torch.cuda.is_available():
+    args.cpu = True
+
+import comfy.ops as ops  # noqa: E402
+import comfy.text_encoders.llama as llama  # noqa: E402
+
+
+def _make_model():
+    config = llama.Llama2Config(
+        vocab_size=16, hidden_size=8, intermediate_size=8,
+        num_hidden_layers=1, num_attention_heads=2, num_key_value_heads=2,
+    )
+    config.head_dim = 4
+    config.fixed_kv = True
+    return llama.Llama2_(config, device="cpu", dtype=torch.float32, ops=ops.manual_cast)
+
+
+def test_init_kv_cache_on_cpu_does_not_probe_cuda_capability(monkeypatch):
+    def _raise_if_not_cuda(device):
+        if torch.device(device).type != "cuda":
+            raise ValueError(f"Expected a cuda device, but got: {device}")
+        return True
+
+    monkeypatch.setattr(
+        llama.comfy_kitchen, "flash_attention_decode_is_available", _raise_if_not_cuda
+    )
+
+    model = _make_model()
+    past = model.init_kv_cache(1, 4, torch.device("cpu"), torch.float32)
+
+    assert not isinstance(past[0], llama.FixedKV)