title: What's the Git command to determine which commit changed a submodule pointer?
body: <p>I'm dissecting a series of changes made to a git repo, some of which involved a submodule.  I used <code>git blame</code> to find the relevant commit within the submodule, but is there a simple way to locate which commit in my main repo changed the submodule pointer to that commit?</p>
  
  <p>Cue simple diagram:</p>
  
  <pre><code>1 &lt;- 2 &lt;- 3 &lt;- 4 &lt;- 5    (Main chain of commits)
  |    |    |    |    |
  1    1    1    2    2    (Submodule)
  </code></pre>
  
  <p>I have located the commit where submodule #1 changed into submodule #2 (say it's 9d95812e...).  How do I determine the fact that main-commit #4 is where the new submodule commit was first employed?</p>