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

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Message-ID: <CAPDyKFo=GP+uBhGDkYWsLTf+XBmyZpmuu123SGMGeeyOge5x4w@mail.gmail.com>
Date: Tue, 3 Sep 2024 12:13:19 +0200
From: Ulf Hansson <ulf.hansson@...aro.org>
To: Geert Uytterhoeven <geert@...ux-m68k.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

On Mon, 2 Sept 2024 at 16:43, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>
> 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...

Should we really care about those silly long names? And are those
really a problem from genpd debugfs point of view?

That said, I don't have a suggestion for a new value of the table
width, but I am certainly open to adjusting it to whatever you
propose.

Kind regards
Uffe