git - How to keep a branch synchronized/updated with master?

Question

At the moment git is doing my head in, I cannot come up with the best solution for the following.

There are two branches, one called master and one called mobiledevicesupport. I want to keep mobiledevicesupport as a continuous branch that will be merged/synced with the master branch whenever mobiledevicesupport is stable. This would merge changes from mobiledevicesupport into master but also bring all the changes from master into mobiledevicesupport so that branch can continue to be worked on and the features improved or amended. This needs to work with a central repository and multiple developers.

Please an example of similar workflows other people use or just tell me if this idea is stupid and I should consider other options. At the moment the workflow seems sound, but I just don't know how I can make git work this way.

Thanks, all help much appreciated.

Update 1: If I was to merge master into mobiledevicesupport and mobiledevice support into master, do I get replicated commits across both branches. Or is git smart enough to work out that I have pulled the latest changes from branch A into branch B and add merge commit C to branch B. And I have pulled the latest changes from branch B into branch A and add merge commit D to branch A?

I was going to post an image but I don't have enough reputation for it, so I guess the following illustration will have to do. Two branches continuously running with merges going both directions often. The key thing I am not sure about is how git will play out the commits and will it fill either branch with the commits from the other branch on merges or will it stay clean. I have used rebase before but it seems to end the branch and put all the commits into the master, or I did it wrong. Thanks for the help so far.

master
A--B--C-----H--I--J--M--N
          /    
mobile   /      
D--E--F--G--------K--L

Answer 1

yes just do

git checkout master
git pull
git checkout mobiledevicesupport
git merge master

to keep mobiledevicesupport in sync with master

then when you're ready to put mobiledevicesupport into master, first merge in master like above, then ...

git checkout master
git merge mobiledevicesupport
git push origin master

and thats it.

the assumption here is that mobilexxx is a topic branch with work that isn't ready to go into your main branch yet. So only merge into master when mobiledevicesupport is in a good place