linux-kernel - Re: [PATCH] drivers/of: Add devm_of

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Message-ID: <5d932502d9985cdfa6540480ea5ce6b0730502a1.camel@kernel.crashing.org>
Date:   Wed, 13 Jun 2018 08:58:34 +1000
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drivers/of: Add devm_of_iomap()

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.