[question] retrieve some patches from another repository

Hi,

Sorry to disturb you. I know this mail list is mainly for git development. Till now I have not found some normal user mail list, at last I choose it to ask a question.

My target is: repository A - linux upstream: a->b->c->d->[merge from repository B]->e->f repository B - a maintainer's tree: x->y->z->[merge from repository A]->... I want to retrieve the patches for one driver and its related changes from commit "a" till maintainer's master.

So I do as this:
* git checkout repo B's master
* because maintainer's tree is derived from upstream point "a" will be included,
  use git format-patch repo a source-code-name

There are 2 issues in it:
* merge point will cause duplicated patch generated, for example repo B has x,
  y, z, then accepted by repo A in merge point, and then merge back to repo B
  (they are different with commit id), they will generate 2 twice.
* some commits do not only change the driver source code, and they change some
  other files also. Unfortunately git format-patch cut them. It cause compile
  error.

My question:
  Does some one know git have the ability to do it or do I need to do it
manually?