Need suggestions on quitting a computer science PhD
Well i have been in similar situation like yours. I chose not to give up and that is why i was able to defend my PhD last month. 

It was very frustrating.I switched advisers 4 times. Would you believe that? I was recommended to be expelled from the PhD program. My situation was much worse than yours. I was almost thrown out of the PhD program in 2010. How i was able to change this? Just like you, i interned in Silicon Valley in 2009 and 2010 where my manager sort of liked me and he stood for me. He and even his manager wrote two letters in my favor supporting that i should not be expelled from the PhD program. They argued that i should switch topic and adviser and continue PhD program. All i was looking for was a good adviser who could trust my skills and luckily i got it.

After that, it was fine. The moral of the story is " i did not give up in circumstances much worse than yours." Does your current adviser like you, have trust in you, have confidence in you? If so, don't worry. Regarding publications, choose mid-tier conferences first to raise your confidence and then go for top-tier conferences.

And now on communities like stackoverflow and various forums for hardware and software, discuss your ideas with experts, shape your ideas here. Talk to your contacts in the industry as to what do they think of your problem or in their opinion what are the hot problems to solve.

Another lesson is be pro-active. Don't procrastinate or live in your own world. Get up