linux-kernel - Re: [PATCH v2 3/7] pmdomain: core: Use dev_name() instead of kobject_get

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Message-ID: <CAMuHMdXM2qHGzcLDfZQNC1Zqj_vh72S9+rV6-xuM+p=w7-oHyQ@mail.gmail.com>
Date: Mon, 2 Sep 2024 16:42:58 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Ulf Hansson <ulf.hansson@...aro.org>
Cc: "Rafael J . Wysocki" <rafael@...nel.org>, Sudeep Holla <sudeep.holla@....com>, linux-pm@...r.kernel.org, 
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>, Nikunj Kela <nkela@...cinc.com>, 
	Prasad Sodagudi <psodagud@...cinc.com>, Maulik Shah <quic_mkshah@...cinc.com>, 
	Daniel Lezcano <daniel.lezcano@...aro.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>, linux-rt-users@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	"open list:TI ETHERNET SWITCH DRIVER (CPSW)" <linux-omap@...r.kernel.org>
Subject: Re: [PATCH v2 3/7] pmdomain: core: Use dev_name() instead of
 kobject_get_path() in debugfs

Hi Ulf,

On Fri, Aug 30, 2024 at 5:50 PM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> On Tue, Aug 20, 2024 at 10:58 AM Ulf Hansson <ulf.hansson@...aro.org> wrote:
> > On Tue, 20 Aug 2024 at 10:55, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > > On Mon, May 27, 2024 at 4:27 PM Ulf Hansson <ulf.hansson@...aro.org> wrote:
> > > > Using kobject_get_path() means a dynamic memory allocation gets done, which
> > > > doesn't work on a PREEMPT_RT based configuration while holding genpd's raw
> > > > spinlock.
> > > >
> > > > To fix the problem, let's convert into using the simpler dev_name(). This
> > > > means the information about the path doesn't get presented in debugfs, but
> > > > hopefully this shouldn't be an issue.
> > > >
> > > > Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
> > > > ---
> > > > Changes in v2:
> > > >         - New patch.
> > >
> > > Thanks for your patch, which is now commit 9094e53ff5c86ebe ("pmdomain:
> > > core: Use dev_name() instead of kobject_get_path() in debugfs")
> > > in pmdomain/next.
> > >
> > > > --- a/drivers/pmdomain/core.c
> > > > +++ b/drivers/pmdomain/core.c
> > > > @@ -3215,16 +3214,9 @@ static int genpd_summary_one(struct seq_file *s,
> > > >         }
> > > >
> > > >         list_for_each_entry(pm_data, &genpd->dev_list, list_node) {
> > > > -               kobj_path = kobject_get_path(&pm_data->dev->kobj,
> > > > -                               genpd_is_irq_safe(genpd) ?
> > > > -                               GFP_ATOMIC : GFP_KERNEL);
> > > > -               if (kobj_path == NULL)
> > > > -                       continue;
> > > > -
> > > > -               seq_printf(s, "\n    %-50s  ", kobj_path);
> > > > +               seq_printf(s, "\n    %-50s  ", dev_name(pm_data->dev));
> > >
> > > While some of the old names didn't even fit in 50 characters, the new
> > > names need much less space, so perhaps this is a good opportunity to
> > > decrease the table width?
> >
> > Sure, it seems reasonable! Do you want to send a patch?
>
> I started looking into it.  Then I noticed that on some systems
> (e.g. TI am335x) the device names may have a longer format than
> the typical <unit-address>.<nodename>. So I wanted to verify on
> BeagleBone Black, but recent kernels crash during early boot.
> Apparently that platform was broken between v6.8 and v6.9-rc1.
> And during bisection, I encountered 3 different failure modes...
>
> To be continued...

The longest generic node names documented in the Devicetree
Specification are "air-pollution-sensor" and "interrupt-controller"
(both counting 20 characters), so a typical device name needs 8
(32-bit unit address) + 1 (dot) + 20 = 29 characters.
However, I assume some devices lie outside the 32-bit address space,
and thus need more space?

With the BeagleBone Black boot issue fixed:
"/devices/platform/ocp/5600fe00.target-module"
resp. "/devices/platform/ocp/44c00000.interconnect/44c00000.interconnect:segment@...000/44e3e074.target-module"
are now shortened to "5600fe00.target-module" resp. "44e3e074.target-module".
However, "/devices/platform/ocp/48000000.interconnect/48000000.interconnect:segment@...000/48000000.interconnect:segment@...000:target-module@0"
is shortened to "48000000.interconnect:segment@...000:target-module@0",
which is still longer than the old column width...

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds