As far as I am concerned helm restart only the pods which are affected by upgrade

If You want to restart ALL pods you can use --recreate-pods flag

--recreate-pods -> performs pods restart for the resource if applicable

For example if You have dashboard chart, You can use this command to restart every pod.

helm upgrade --recreate-pods -i k8s-dashboard stable/k8s-dashboard

There is a github issue which provide another workaround for it

Every time you need to restart the pods, change the value of that annotation. A good annotation could be timestamp

First, add an annotation to the pod. If your chart is of kind Deployment, add annotation to spec.template.metadata.annotations. For example:

kind: Deployment
spec:
  template:
    metadata:
      labels:
        app: ecf-helm-satellite-qa
      annotations:
        timestamp: "{{ .Values.timestamp }}"

Deploy that. Now, every time you set timestamp in helm command. Kubernetes will rollout a new update without downtime.

helm upgrade ecf-helm-satellite-qa . --set-string timestamp=a_random_value