linux-kernel - Re: [PATCH] powercap: intel_rapl: Do not change CLAMPING bit if ENABLE bit cannot be changed

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Message-ID: <d2f0b3fa448d11536c26b98067d400a44d9d3010.camel@intel.com>
Date: Wed, 18 Jun 2025 23:33:17 +0000
From: "Zhang, Rui" <rui.zhang@...el.com>
To: "rafael@...nel.org" <rafael@...nel.org>
CC: "srinivas.pandruvada@...ux.intel.com"
	<srinivas.pandruvada@...ux.intel.com>, "linux-pm@...r.kernel.org"
	<linux-pm@...r.kernel.org>, "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] powercap: intel_rapl: Do not change CLAMPING bit if
 ENABLE bit cannot be changed

On Wed, 2025-06-18 at 19:04 +0200, Rafael J. Wysocki wrote:
> On Wed, Jun 18, 2025 at 5:03 AM Zhang Rui <rui.zhang@...el.com> wrote:
> > 
> > PL1 cannot be disabled on some platforms. The ENABLE bit is still set
> > after software clears it. This behavior leads to a scenario where,
> > upon
> > user request to disable the Power Limit through the powercap sysfs,
> > the
> > ENABLE bit remains set while the CLAMPING bit is inadvertently
> > cleared.
> > 
> > According to the Intel Software Developer's Manual, the CLAMPING bit,
> > "When set, allows the processor to go below the OS requested P states
> > in
> > order to maintain the power below specified Platform Power Limit
> > value."
> > 
> > Thus this means the system may operate at higher power levels than
> > intended on such platforms.
> > 
> > Enhance the code to check ENABLE bit after writing to it, and stop
> > further processing if ENABLE bit cannot be changed.
> > 
> > Reported-by: Srinivas Pandruvada
> > <srinivas.pandruvada@...ux.intel.com>
> 
> If this is a fix, I would appreciate a Fixes: tag.

The problem is always there since Day One, in this commit 2d281d8196e3
("PowerCap: Introduce Intel RAPL power capping driver").

I can use this commit in the Fixes tag. And I think this should be stable
candidate. Will send V2 soon.

thanks,
rui
> 
> > Signed-off-by: Zhang Rui <rui.zhang@...el.com>
> > ---
> >  drivers/powercap/intel_rapl_common.c | 17 ++++++++++++++++-
> >  1 file changed, 16 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/powercap/intel_rapl_common.c
> > b/drivers/powercap/intel_rapl_common.c
> > index e3be40adc0d7..602f540cbe15 100644
> > --- a/drivers/powercap/intel_rapl_common.c
> > +++ b/drivers/powercap/intel_rapl_common.c
> > @@ -341,12 +341,27 @@ static int set_domain_enable(struct
> > powercap_zone *power_zone, bool mode)
> >  {
> >         struct rapl_domain *rd =
> > power_zone_to_rapl_domain(power_zone);
> >         struct rapl_defaults *defaults = get_defaults(rd->rp);
> > +       u64 val;
> >         int ret;
> > 
> >         cpus_read_lock();
> >         ret = rapl_write_pl_data(rd, POWER_LIMIT1, PL_ENABLE, mode);
> > -       if (!ret && defaults->set_floor_freq)
> > +       if (ret)
> > +               goto end;
> > +
> > +       ret = rapl_read_pl_data(rd, POWER_LIMIT1, PL_ENABLE, false,
> > &val);
> > +       if (ret)
> > +               goto end;
> > +
> > +       if (mode != val) {
> > +               pr_debug("%s cannot be %s\n", power_zone->name, mode
> > ? "enabled" : "disabled");
> > +               goto end;
> > +       }
> > +
> > +       if (defaults->set_floor_freq)
> >                 defaults->set_floor_freq(rd, mode);
> > +
> > +end:
> >         cpus_read_unlock();
> > 
> >         return ret;
> > --
> > 2.43.0
> > 
> >