On Wed, Aug 27, 2014 at 11:34:32AM +0100, Grant Likely wrote: > On Tue, 26 Aug 2014 11:11:07 +0100, Mark Rutland <mark.rutland@xxxxxxx> wrote: > > On Tue, Aug 26, 2014 at 10:42:04AM +0100, Alexander Holler wrote: > > > Am 26.08.2014 10:49, schrieb Thierry Reding: > > > > On Tue, Aug 26, 2014 at 09:42:08AM +0100, Grant Likely wrote: > > > >> On Mon, 25 Aug 2014 15:37:16 +0200, Thierry Reding <thierry.reding@xxxxxxxxx> wrote: > > > > [...] > > > >>> There are somewhat standardized bindings for the above and especially > > > >>> for bindings of the type that clocks implement this is trivial. We can > > > >>> simply iterate over each (phandle, specifier) tuple and check that the > > > >>> corresponding clock provider can be resolved (which typically means that > > > >>> it's been registered with the common clock framework). > > > >>> > > > >>> For regulators (and regulator-like bindings) the problem is somewhat > > > >>> more difficult because they property names are not standardized. One way > > > >>> to solve this would be to look for property names with a -supply suffix, > > > >>> but that could obviously lead to false positives. One alternative that I > > > >>> think could eliminate this would be to explicitly list dependencies in > > > >>> drivers. This would allow core code to step through such a list and > > > >>> resolve the (phandle, specifier) tuples. > > > >> > > > >> False positives and negatives may not actually be a problem. It is > > > >> suboptimal, certainly, but it shouldn't outright break the kernel. > > > > > > > > There could be cases where some random integer in a cell could be > > > > interpreted as a phandle and resolve to a struct device_node. I suppose > > > > it might be unlikely, but not impossible, that the device_node could > > > > even match a device in the correct subsystem and you'd get a wrong > > > > dependency. Granted, a wrong dependency may not be catastrophic in that > > > > it won't lead to a crash, but it could lead to various kinds of > > > > weirdness and hard to diagnose problems. > > > > > > You need either the type information in the DTB (that's why I've add > > > those "dependencies" to identify phandles), or you need to know every > > > binding (at "dependency-resolve-time" to identify phandles. > > > > While having type information in the DTB would be fantastic, it's not > > something we can expect from the systems already in the wild, and I > > worry how it would interact with bootloaders that modify the DTB (I > > don't know if any modify properties with phandles). > > Anything we do here is firmly in the realm of optimization and > improvement. Adding data to the tree is fine as long as we don't make > the kernel depend on it. Older platforms will continue to work without > the optimization. It's not just optimisation but an important feature for new arm64 SoCs. Given some Tegra discussions recently, in many cases the machine_desc use on arm is primarily to initialise devices in the right order. If we can solve this in a more deterministic way (other than deferred probing), we avoid the need for a dedicated SoC platform driver (or machine_desc) or workarounds like different initcall levels and explicit DT parsing. -- Catalin -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
