KS2012: ARM: Process review for the arm-soc tree

Arnd Bergmann and Olof Johansson started day two of the ARM minisummit with a look at the arm-soc tree that they have been managing. They wanted to go over what has happened with the tree during the last year to see what was working and what could be improved. We are "trying to make you all happy", Bergmann said, while also trying to keep Linus Torvalds happy, which are conflicting goals at times.

The work split between the two has worked well, Bergmann said. When one of them has no time, the other has been able to pick up the slack. From a personal perspective, Bergmann said he is most unhappy when he has to reject a patch set. Actually it is worse when he has to make a decision about patches; some are easy to reject out of hand, but others are more difficult. If a huge patch set comes in, perhaps late in terms of getting it ready for the next merge window, or with lots of good patches but some that do "really nasty" things, he has to decide whether to reject it or not.

One thing to note, Bergmann said, is that Torvalds said that he is "not totally hating our guts anymore" in the Kernel Summit. That's progress. Paul Walmsley asked what things Torvalds is most sensitive to in terms of the ARM tree these days. Bergmann said that he was not sure what the problems are now, but, in the past, the totally uncoordinated nature of ARM development was the main problem.

It used to be that Torvalds would get 15 pull requests for various sub-architectures. That could lead to lots of merge conflicts and dependencies between trees, which annoyed him. The last merge window didn't have many of those problems. The number of patches was down slightly, but not hugely, and not enough to explain that reduction, Bergmann said.

Walmsley followed up by asking what the arm-soc maintainers would like to see from the sub-architecture maintainers. Johansson said that using signed Git tags would be very nice. That helps because the commit message ends up in the merge commit. It also identifies that the patches came from who they purport to, but the most important thing that signed tags bring is that message in the merge commit. Bergmann added that he tries to come up with something for the merge commit if there is no signed tag, but he would much rather get something from the maintainer directly.

One of the goals of the arm-soc tree is to facilitate (and force) the ARM cleanup process. The hope was that it would help pressure maintainers' managers to free up more time for that work. Bergmann asked if that process was working. Linus Walleij noted that the best pressure on management comes from customers, which, for him, are the handset and equipment manufacturers. Those manufacturers or Google make for an effective lever to change things. He is not sure how it came about (and Bergmann expressed surprise as well) but some customers are now asking for device tree support, which makes it easier to convince his management to spend time on that work.

Pushback from distributions is missing currently, Tony Lindgren said. Right now, ARM is distribution-unfriendly; device makers and SoC vendors are not getting the feedback to fix that. Walmsley wondered if the distribution and customer requirements would be in conflict, which could lead to problems.

Lindgren said that he sees tablets running different distributions in the future, but the device makers may not know what the distributions need. But Johansson cautioned that device makers aren't very interested in hearing from those who aren't shipping significant volumes of their product. Volumes of five and even six-digit numbers just aren't of that much interest to the device makers. For the most part those manufacturers are just following Android, Stephen Warren added.

Ben Dooks was concerned that ARM driver maintenance would suffer as those drivers move out of the arch/arm tree. Bergmann disagreed with that assessment because he thinks the overall work will become easier. The drivers will be centralized and use the same frameworks, so the maintenance burden will actually decrease.

Overall, there weren't many complaints about how things are going. For the most part, participants seemed pleased with how the arm-soc tree, and the overall ARM development process, was working. There's still plenty to do, but the process piece seems largely nailed down.