add freeze/unfreeze options

src/lerobot/policies/xvla/configuration_xvla.py

@@ -84,6 +84,13 @@ class XVLAConfig(PreTrainedConfig):
     num_image_views: int | None = None
     empty_cameras: int = 0
 
+    # Freezing options for VLM components
+    # By default, VLM encoders are frozen and only policy transformer + soft prompts train
+    freeze_vision_encoder: bool = True  # Freeze VLM vision encoder weights
+    freeze_language_encoder: bool = True  # Freeze VLM language encoder weights
+    train_policy_transformer: bool = True  # Allow policy transformer to train
+    train_soft_prompts: bool = True  # Allow soft prompts to train
+
     # Training presets
     optimizer_lr: float = 1e-4
     optimizer_betas: tuple[float, float] = (0.9, 0.95)

src/lerobot/policies/xvla/modeling_xvla.py

@@ -83,6 +83,55 @@ class XVLAModel(nn.Module):
             use_hetero_proj=config.use_hetero_proj,
         )
 
+        # Apply freezing based on config
+        self._apply_freezing()
+
+    def _apply_freezing(self) -> None:
+        """
+        Freeze VLM vision and language encoders based on config options.
+        Keep only policy transformer and soft prompts trainable.
+        """
+        # Freeze vision encoder
+        if self.config.freeze_vision_encoder and hasattr(self.vlm, "vision_tower"):
+            for param in self.vlm.vision_tower.parameters():
+                param.requires_grad = False
+
+        # Freeze language encoder
+        if self.config.freeze_language_encoder and hasattr(self.vlm, "language_model"):
+            lm = self.vlm.language_model
+            # Freeze encoder
+            if hasattr(lm, "model") and hasattr(lm.model, "encoder"):
+                for param in lm.model.encoder.parameters():
+                    param.requires_grad = False
+            # Freeze shared embeddings
+            if hasattr(lm, "model") and hasattr(lm.model, "shared"):
+                for param in lm.model.shared.parameters():
+                    param.requires_grad = False
+
+        # Freeze or unfreeze policy transformer
+        if not self.config.train_policy_transformer:
+            for name, param in self.transformer.named_parameters():
+                if "soft_prompts" not in name:
+                    param.requires_grad = False
+
+        # Freeze or unfreeze soft prompts
+        if not self.config.train_soft_prompts and hasattr(self.transformer, "soft_prompt_hub"):
+            for param in self.transformer.soft_prompt_hub.parameters():
+                param.requires_grad = False
+
+    def get_trainable_params_summary(self) -> dict[str, int]:
+        """
+        Returns a summary of trainable vs frozen parameters.
+        """
+        trainable = sum(p.numel() for p in self.parameters() if p.requires_grad)
+        frozen = sum(p.numel() for p in self.parameters() if not p.requires_grad)
+        return {
+            "trainable": trainable,
+            "frozen": frozen,
+            "total": trainable + frozen,
+            "trainable_pct": 100.0 * trainable / (trainable + frozen) if (trainable + frozen) > 0 else 0.0,
+        }
+
     def forward_vlm(
         self,
         input_ids: torch.LongTensor,
@@ -197,13 +246,25 @@ class XVLAPolicy(PreTrainedPolicy):
         self.model = XVLAModel(config=config, florence_config=florence_config, proprio_dim=proprio_dim)
         self.reset()
 
+        # Log trainable parameters summary
+        params_summary = self.model.get_trainable_params_summary()
+        print("XVLA Parameter Summary:")
+        print(f"  Trainable: {params_summary['trainable']:,} ({params_summary['trainable_pct']:.2f}%)")
+        print(f"  Frozen: {params_summary['frozen']:,}")
+        print(f"  Total: {params_summary['total']:,}")
+        print(f"  Vision Encoder: {'Frozen' if config.freeze_vision_encoder else 'Trainable'}")
+        print(f"  Language Encoder: {'Frozen' if config.freeze_language_encoder else 'Trainable'}")
+        print(f"  Policy Transformer: {'Trainable' if config.train_policy_transformer else 'Frozen'}")
+        print(f"  Soft Prompts: {'Trainable' if config.train_soft_prompts else 'Frozen'}")
+
     def reset(self) -> None:
         self._queues = {
             ACTION: deque(maxlen=self.config.n_action_steps),
         }
 
     def get_optim_params(self) -> dict:
-        return self.parameters()
+        """Return only trainable parameters for optimization."""
+        return filter(lambda p: p.requires_grad, self.parameters())
 
     def _prepare_state(self, batch: dict[str, Tensor], batch_size: int, device: torch.device) -> Tensor:
         if not self.config.use_proprio or OBS_STATE not in batch:

src/lerobot/policies/xvla/utils.py

@@ -1,5 +1,72 @@
+import math
+
 import numpy as np
-import robosuite.utils.transform_utils as transform_utils
+
+
+def mat2quat(rmat):
+    """
+    Converts given rotation matrix to quaternion.
+
+    Args:
+        rmat (np.array): 3x3 rotation matrix
+
+    Returns:
+        np.array: (x,y,z,w) float quaternion angles
+    """
+    mat = np.asarray(rmat).astype(np.float32)[:3, :3]
+
+    m00 = mat[0, 0]
+    m01 = mat[0, 1]
+    m02 = mat[0, 2]
+    m10 = mat[1, 0]
+    m11 = mat[1, 1]
+    m12 = mat[1, 2]
+    m20 = mat[2, 0]
+    m21 = mat[2, 1]
+    m22 = mat[2, 2]
+    # symmetric matrix k
+    k = np.array(
+        [
+            [m00 - m11 - m22, np.float32(0.0), np.float32(0.0), np.float32(0.0)],
+            [m01 + m10, m11 - m00 - m22, np.float32(0.0), np.float32(0.0)],
+            [m02 + m20, m12 + m21, m22 - m00 - m11, np.float32(0.0)],
+            [m21 - m12, m02 - m20, m10 - m01, m00 + m11 + m22],
+        ]
+    )
+    k /= 3.0
+    # quaternion is Eigen vector of k that corresponds to largest eigenvalue
+    w, v = np.linalg.eigh(k)
+    inds = np.array([3, 0, 1, 2])
+    q1 = v[inds, np.argmax(w)]
+    if q1[0] < 0.0:
+        np.negative(q1, q1)
+    inds = np.array([1, 2, 3, 0])
+    return q1[inds]
+
+
+def quat2axisangle(quat):
+    """
+    Converts quaternion to axis-angle format.
+    Returns a unit vector direction scaled by its angle in radians.
+
+    Args:
+        quat (np.array): (x,y,z,w) vec4 float angles
+
+    Returns:
+        np.array: (ax,ay,az) axis-angle exponential coordinates
+    """
+    # clip quaternion
+    if quat[3] > 1.0:
+        quat[3] = 1.0
+    elif quat[3] < -1.0:
+        quat[3] = -1.0
+
+    den = np.sqrt(1.0 - quat[3] * quat[3])
+    if math.isclose(den, 0.0):
+        # This is (close to) a zero degree rotation, immediately return
+        return np.zeros(3)
+
+    return (quat[:3] * 2.0 * math.acos(quat[3])) / den
 
 
 def rotate6d_to_axis_angle(r6d):
@@ -30,8 +97,8 @@ def rotate6d_to_axis_angle(r6d):
 
     axis_angle_list = []
     for i in range(rotation_matrix.shape[0]):
-        quat = transform_utils.mat2quat(rotation_matrix[i])
-        axis_angle = transform_utils.quat2axisangle(quat)
+        quat = mat2quat(rotation_matrix[i])
+        axis_angle = quat2axisangle(quat)
         axis_angle_list.append(axis_angle)
 
     axis_angle_array = np.stack(axis_angle_list, axis=0)  # shape: (N, 3)