On Wed, Nov 7, 2012 at 12:54 AM, Mitch Bradley <wmb@xxxxxxxxxxxxx> wrote: > On 11/6/2012 12:37 PM, Stephen Warren wrote: >> This proposal is very oriented at an overlay-based approach. I'm not >> totally convinced that a pure overlay approach (as in how dtc does >> overlayed DT nodes) will be flexible enough, but would love to be >> persuaded. Again see below. > > > An overlay approach will not be powerful enough to solve the sorts of > problems that occur when a product goes into full production, becomes a > family, and starts to evolve. Issues like second-source parts that > aren't quite compatible and need to be detected and reported, > board-stuff options for different customer profiles, speed grades of > parts that aren't properly probeable but instead need to be identified > by some subterfuge, the list of tedious issues goes on and on. > > It's nice to pretend that the world fits into a few coherent simple > use cases, but 30 years of experience shipping computer product families > proves otherwise. You need a programming language to solve the full > set of problems - which I why the device tree is designed so it can > be generated and modified by a program. I'm not going to argue with that. There is nothing saying that the overlay wouldn't be generated or applied by a script. However, I do strongly think that the data model needs to be independent of any tool or execution environment used to manipulate it. I certainly am not interested in encoding scripts or bytecode into the tree - the opposite of the approach used by ACPI which must execute AML to even retrieve the device tree. I like the overlay approach because it is conceptually straightforward and provides a working model of how changes could be made from userspace while still being usable by firmware. An alternate approach from userspace would be to use a live virtual filesystem to manipulate the device tree, though that approach only applies to Linux userspace. Firmware would still need its own approach. g. -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
