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). > The latter is impracticable to implement in a generic way (for use > with every possible binding). I don't think we necessarily need dependency information for every binding and driver. We only need dependency information where a device has a dependency on another device and we don't currently have an explicit probe ordering guaranteed by Linux. Where a device driver lacks dependency information and fails to probe, we can fall back to the current deferred probing. Do we have any worst case example systems / drivers / dts? Thanks, Mark. -- 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
