Mis?use of aliases

On Sat, Jul 14, 2012 at 07:07:17AM -1000, Mitch Bradley wrote:

On 7/14/2012 6:37 AM, David Gibson wrote:

quoted

On Fri, Jul 13, 2012 at 07:30:42PM -1000, Mitch Bradley wrote:

quoted

quoted

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.

quoted

	prop = <&fred>;
Will generate a phandle valued property, but
	prop = &fred;
Will generate a string (path) valued property.

quoted

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