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

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Date:   Wed, 13 Jun 2018 10:18:24 +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 Wed, 2018-06-13 at 02:16 +0300, Andy Shevchenko wrote:
> On Wed, Jun 13, 2018 at 1:58 AM, Benjamin Herrenschmidt
> <benh@...nel.crashing.org> wrote:
> > 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.
> 
> Because your patch does nothing except another layring of the existing APIs.

I'm really having a hard time understanding what you are going on
about..

Yes, it's a helper that combines two existing API functions, the goal
being to generally replace the use of the existing of_iomap whenever
possible. It makes sense and makes callers simpler and less bug prone.

> 
> > 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).
> 
> Hmm... So, you are trying to solve problem with other methods which
> might be not so suitable at all?

Again, I cannot understand what you are going on about, what is "not
suitable" to what purpose ?

It's fairly common for nodes to point to each other. We've been doing
that since the dawn of the device-tree.

In this case, we have a coprocessor bound to a device and pointing to
its interrupt controller, and we need to get to that and map it, I fail
to see what the issue is and in what way this is "not suitable".

But there are many other uses of things like of_iomap() which could
benefit from switching to devm_of_iomap() and thus getting the
automated cleanup on exit and appropriate request of the memory
resource.

(hint: I wrote of_iomap and a good bulk of what's in
drivers/of/address.c...

Ben.