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SubjectRe: [PATCH 03/17] base: fix order of OF initialization
On Wed, Jun 07, 2017 at 08:49:43PM -0700, Frank Rowand wrote:
> On 06/07/17 11:39, Wesley Terpstra wrote:
> > It was a while ago that I debugged this. I already reported this bug
> > to Benjamin Herrenschmidt (now in CC), and I believe he has a patch of
> > his own to fix the same issue.
> >
> > As I understand it, of_core_init sets up the OF entries in
> > /sys/firmware/devicetree. During platform bringup, when the system
> > describes the cpu + cache hierarchy, it also makes an of_node symlink
> > into that directory. However, if it doesn't exist yet, you get the
> > warning.
> >
> > # ls -l /sys/devices/system/cpu/cpu3/of_node
> > lrwxrwxrwx 1 root root 0 Jan 1 00:00
> > /sys/devices/system/cpu/cpu3/of_node ->
> > ../../../../firmware/devicetree/base/cpus/cpu@3
> >
> > On Wed, Jun 7, 2017 at 2:35 AM, Mark Rutland <mark.rutland@arm.com> wrote:
> >> On Wed, Jun 07, 2017 at 09:07:20AM +0200, Geert Uytterhoeven wrote:
> >>> CC devicetree folks
> >>>
> >>> On Wed, Jun 7, 2017 at 12:59 AM, Palmer Dabbelt <palmer@dabbelt.com> wrote:
> >>>> From: "Wesley W. Terpstra" <wesley@sifive.com>
> >>>>
> >>>> This fixes: [ 0.010000] cpu cpu0: Error -2 creating of_node link
> >>>> ... which you get for every CPU on all architectures with a OF cpu/ node.
> >>
> >> I take it this means a /cpus node? Or the /cpus/cpu@* nodes?
> >>
> >> I'm not seeing this on arm64 when booting v4.12-rc4 with DT, so clearly
> >> this doesn't affect all such architectures.
> >>
> >> What path are these errors happening in?
>
> On the surface, the patch looks reasonable. But it is not obvious to me why
> the error message is occurring. I would like to understand the cause before
> saying the patch is good.
>
> What kernel version is showing the error? For a specific architecture
> (the patch lists 'riscv, nios, etc'), which config and device tree source?
>
> And again, what is the calling path?

From having grepped around, I think this affects architectures which
select CONFIG_GENERIC_CPU_DEVICES, which includes nios2.

In that case, driver_init() calls cpu_dev_init() before calling
of_core_init(). Then we get the callchain:

cpu_dev_init()
-> cpu_dev_register_generic()
-> register_cpu(cpu, i)
-> device_register(&cpu->dev)
-> device_add(dev)
-> device_add_class_symlinks(dev)

... in device_add_class_symlinks, we we dev->of_node, and call
sysfs_create_link(), which fails because we haven't called
of_core_init() to register the sysfs devicetree directory yet.

Given that, this patch makes sense to me.

FWIW, with the commit message updated to describe the particular
ordering problem:

Acked-by: Mark Rutland <mark.rutland@arm.com>

Thanks,
Mark.

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