linux-kernel - Re: [PATCH] drivers/of: Introduce ARCH_HAS_OWN_OF

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Message-ID: <CAL_Jsq+ho2QhmNmPZMDJcfSxposJd=jYDvjhXH8cMAtVFP7n4A@mail.gmail.com>
Date:   Mon, 9 Apr 2018 15:52:38 -0500
From:   Rob Herring <robh@...nel.org>
To:     "Oliver O'Halloran" <oohall@...il.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        linux-nvdimm@...ts.01.org, devicetree@...r.kernel.org,
        sparclinux@...r.kernel.org,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH] drivers/of: Introduce ARCH_HAS_OWN_OF_NUMA

On Mon, Apr 9, 2018 at 2:46 AM, Oliver O'Halloran <oohall@...il.com> wrote:
> Some OF platforms (pseries and some SPARC systems) has their own
> implementations of NUMA affinity detection rather than using the generic
> OF_NUMA driver, which mainly exists for arm64. For other platforms one
> of two fallbacks provided by the base OF driver are used depending on
> CONFIG_NUMA.
>
> In the CONFIG_NUMA=n case the fallback is an inline function in of.h.
> In the =y case the fallback is a real function which is defined as a
> weak symbol so that it may be overwritten by the architecture if desired.
>
> The problem with this arrangement is that the real implementations all
> export of_node_to_nid(). Unfortunately it's not possible to export the
> fallback since it would clash with the non-weak version. As a result
> we get build failures when:
>
> a) CONFIG_NUMA=y && CONFIG_OF=y, and
> b) The platform doesn't implement of_node_to_nid(), and
> c) A module uses of_node_to_nid()
>
> Given b) will be true for most platforms this is fairly easy to hit
> and has been observed on ia64 and x86.

How specifically do we hit this? The only module I see using
of_node_to_nid in mainline is Cell EDAC driver.

> This patch remedies the problem by introducing the ARCH_HAS_OWN_OF_NUMA
> Kconfig option which is selected if an architecture provides an
> implementation of of_node_to_nid(). If a platform does not use it's own,
> or the generic OF_NUMA, then always use the inline fallback in of.h so
> we don't need to futz around with exports.

I'm more inclined to figure out how to remove the export and provide a
non DT specific function if drivers need to know this.

Rob