src/transformers/models/ibert/quant_modules.py/FixedPointMul/backward
class FixedPointMul:    def backward(ctx, grad_output):
        identity_grad = None
        if ctx.identity is not None:
            identity_grad = grad_output.clone() / ctx.z_scaling_factor
        return grad_output.clone() / ctx.z_scaling_factor, None, None, None, None, identity_grad, None