On Tue, Aug 26, 2014 at 11:11:07AM +0100, Mark Rutland 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). > > > 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? Cc'ing Stéphane who's brought this up not long ago. There seem to be cases where display initialization can be delayed up to 5-6 seconds due to deferred probing (where the system would otherwise take 5-6 seconds to boot). Thierry
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