linux-kernel - Re: [PATCH v6 3/7] powercap/drivers/dtpm: Simplify the dtpm table

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Date:   Fri, 26 Nov 2021 19:18:06 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Doug Smythies <dsmythies@...us.net>,
        Linux PM list <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Lukasz Luba <lukasz.luba@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v6 3/7] powercap/drivers/dtpm: Simplify the dtpm table

On Friday, November 26, 2021 6:43:24 PM CET Daniel Lezcano wrote:
> On 26/11/2021 18:21, Rafael J. Wysocki wrote:
> > Hi Doug,
> > 
> > On Fri, Nov 26, 2021 at 6:08 PM Doug Smythies <dsmythies@...us.net> wrote:
> >>
> >> Hi Daniel,
> >>
> >> This patch introduces a regression, at least on my test system.
> >> I can no longer change CPU frequency scaling drivers, for example
> >> from intel_cpufreq (A.K.A intel_pstate in passive mode) to intel_pstate
> >> (A.K.A. active mode). The task just hangs forever.
> >>
> >> I bisected the kernel and got this commit as the result.
> >> As a double check, I reverted this commit:
> >> 7a89d7eacf8e84f2afb94db5ae9d9f9faa93f01c
> >> on kernel 5.16-rc2 and the issue was resolved.
> >>
> >> While your email is fairly old, I observe that it was only included as of
> >> kernel 5.16-rc1.
> >>
> >> Command Example that never completes:
> >>
> >> $ echo passive | sudo tee /sys/devices/system/cpu/intel_pstate/status
> >>
> >> syslog excerpt attached.
> > 
> > This looks like it may be problematic:
> > 
> > diff --git a/drivers/powercap/dtpm_cpu.c b/drivers/powercap/dtpm_cpu.c
> > index f6076de39540..98841524a782 100644
> > --- a/drivers/powercap/dtpm_cpu.c
> > +++ b/drivers/powercap/dtpm_cpu.c
> > @@ -204,7 +204,7 @@ static int cpuhp_dtpm_cpu_online(unsigned int cpu)
> >        return ret;
> > }
> > 
> > -int dtpm_register_cpu(struct dtpm *parent)
> > +static int __init dtpm_cpu_init(void)
> > {
> >        int ret;
> > 
> > so please try to remove the __init annotation from dtpm_cpu_init() and
> > see if that helps.
> 
> Yes, actually that should be called only if it is configured properly.

What do you mean?

> The dtpm_cpu just initializes itself unconditionally, I did not figured
> out there is the usually allyesconfig used by default by the distros.

Well, it is.

> That should be fixed with a proper DT configuration [1]
> 
> [1]
> https://lore.kernel.org/all/20211124125506.2971069-3-daniel.lezcano@linaro.org/

No, we are talking about systems without any DT at all here.