On Sat, Jul 14, 2012 at 07:07:17AM -1000, Mitch Bradley wrote: > On 7/14/2012 6:37 AM, David Gibson wrote: > > On Fri, Jul 13, 2012 at 07:30:42PM -1000, Mitch Bradley wrote: > >>> I'm not sure this is really a good use of aliases. UARTs use aliases > >>> because it is important that the UART number to tty number is known and > >>> fixed. > >> > >> This brings up an issue that I've been meaning to comment on. > >> > >> The use of phandle-valued properties in the aliases node causes real OFW > >> implementations some amount of heartburn. The Open Firmware standard > >> says that the properties in /aliases are string-valued. That's > >> important, because aliases are shorthand for fragments of full device > >> specifiers (pathnames that can include arguments to nodes). Phandles > >> can point to nodes, but can't be relative, and can't encode > >> per-node-component arguments. > > > > Um, so, properties in /aliases should not have phandle values, flat > > tree or otherwise. Has this been seen in the wild, or are you being > > misled by the fact that dtc's reference-to-phandle and > > reference-to-path syntax is very similar: > > Yes, I was indeed being misled. Thanks for the clarification. The > "&fred" syntax is present in the .dts files that I have looked at. Right, it's all about the context. &label is always a reference to another node, but in cell context < ... > that's expanded as a phandle, in bare context it's expanded as a path. > > prop = <&fred>; > > Will generate a phandle valued property, but > > prop = &fred; > > Will generate a string (path) valued property. > > > >> For binding a Linux unit number to a device node, I would prefer to > >> decorate the node with a property like "linux,unit#", instead of > >> breaking the standard semantics of /aliases. > > > > I don't see how using aliases for unit numbering (inherently) breaks > > the semantics of /aliases. If phandle valued properties are being > > used that is wrong, but it's not necessary for the unit numbering > > anyway. > > I agree, the use of string-valued /aliases is not a semantic problem. > That said, I still think that decorating individual nodes is a better > approach, for locality reasons. But, now that my misunderstanding has > been cleared up, it's a mild preference instead of "heartburn". So, I think aliases was suggested for this sort of numbering precisely because it _isn't_ local. Particularly when numbering similar devices across unrelated busses, the ordering more or less has to be a global platform convention, and may not be derived from - or even contradict - local numbering conventions from individual busses or components. -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson -- 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
