Hi Simon,
2014-10-14 13:50 GMT+09:00 Simon Glass sjg@chromium.org:
Hi,
This question came up at the U-Boot mini-summit yesterday and I was tasked with starting a thread on the mailing list.
There seemed to be a strong feeling in the room that permitting platform data in driver model is a mistake. Reasons mentioned were:
- device tree is how things are done in Linux at least for most
platforms we support
- we can therefore import this directly in from Linux rather than
writing new platform data
- platform data is considered 'legacy' and we should not support
legacy features in a new framework
- device tree permits fully abstracting the device data from the code,
avoiding #ifdefs
- it is easier to change settings in device tree than in platform data
The main impact is that all boards would need at least some sort of device tree when they move to driver model.
There is also the question of SPL, where we are sometimes space-constrained. If we go with this policy I wonder if we should permit an exception for things required by SPL for now? Typically in SPL for these space-constrained platforms we only need a few devices so we could provide platform data for SPL while still using device tree in U-Boot It would be possible to enable device tree in SPL for many platforms but that feels like something that should not block progress. So perhaps platform data in SPL should be a separate question.
Please have a think about this and reply on this thread.
Well, I believe we should allow to use platform data on Normal as well as SPL.
Device Tree is costly in terms of the binary size (it needs to build lib/libfdt and some other files), so we should keep it optional.
I see no benefits of using device tree on U-boot for architectures that do not support it in Linux.