Re: [PATCH] drivers/of: Add devm_of_iomap()

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Tue, 2018-06-12 at 19:53 +0300, Andy Shevchenko wrote:
> 
> > > It feels like a wrong approach.
> > > Can OF graph help here? Would it be better approach?
> > 
> > I don't quite understand what your objection is nor what "OF graph"
> > is...
> 
> There is no objection per se, just a doubt that this is a right thing to do.
> I might be wrong, of course.
> 
> OF graph nodes is a special API that allows you to access like you
> said "different node of device-tree".
> https://elixir.bootlin.com/linux/latest/source/Documentation/devicetree/bindings/graph.txt

So I had a look and this is just an example on how to use phandles to
link ports and endpoints... I fail to see how that relates to what this
patch does.

In the driver I'm doing for example, I do use a similar technique to
"point" to the other node. In this case, this is a coprocessor in the
SoC and I'm linking to the node that represent its interrupt controller
(and its not a full fledged OS running there so we don't have a full
interrupt tree for it).

But once you have such a "graph", the question of mapping whatever
memory resources (ie. "reg" properties) remains.

Today, people will use of_address_to_resource() with ioremap, or
of_iomap () to do that ...

This patch just provides a devm_ variant of the latter, which also does
a request_mem_resource() on it (which is missing from of_iomap), so
generally is a better alternative.

Cheers,
Ben.