code: def validation_step(self, batch, batch_idx):
      x, y = batch
      probs = self(x)
      acc = self.accuracy(probs, y)
      self.log("val_acc", acc)
  
file_path: pytorch-lightning/examples/pytorch/hpu/mnist_sample.py
imports: import torch
  from jsonargparse import lazy_instance
  from lightning.pytorch import LightningModule
  from lightning.pytorch.cli import LightningCLI
  from lightning.pytorch.demos.mnist_datamodule import MNISTDataModule
  from lightning_habana import HPUPrecisionPlugin
  from torch.nn import functional
label_desc: Use image node_id 4 for calling the LitClassifier obj's underlying member method code with example usage: obj.validation_step(batch, batch_idx) without return types