linux-kernel - Re: [PATCH v1 4/4] ACPI: processor: thermal: Update CPU cooling devices on cpufreq policy changes

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Date:   Mon, 13 Mar 2023 14:50:54 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     "Zhang, Rui" <rui.zhang@...el.com>
Cc:     "rafael@...nel.org" <rafael@...nel.org>,
        "viresh.kumar@...aro.org" <viresh.kumar@...aro.org>,
        "daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
        "Wang, Quanxian" <quanxian.wang@...el.com>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>,
        "srinivas.pandruvada@...ux.intel.com" 
        <srinivas.pandruvada@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v1 4/4] ACPI: processor: thermal: Update CPU cooling
 devices on cpufreq policy changes

On Sun, Mar 12, 2023 at 3:44 PM Zhang, Rui <rui.zhang@...el.com> wrote:
>
> On Fri, 2023-03-10 at 19:29 +0100, Rafael J. Wysocki wrote:
> > On Tue, Mar 7, 2023 at 5:47 PM Zhang, Rui <rui.zhang@...el.com>
> > wrote:
> > > On Fri, 2023-03-03 at 20:23 +0100, Rafael J. Wysocki wrote:
> > > > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > > >
> > > > When a cpufreq policy appears or goes away, the CPU cooling
> > > > devices
> > > > for
> > > > the CPUs covered by that policy need to be updated so that the
> > > > new
> > > > processor_get_max_state() value is stored as max_state and the
> > > > statistics in sysfs are rearranged for each of them.
> > > >
> > > > Do that accordingly in acpi_thermal_cpufreq_init() and
> > > > acpi_thermal_cpufreq_exit().
> > > >
> > > > Fixes: a365105c685c("thermal: sysfs: Reuse cdev->max_state")
> > > > Reported-by: Wang, Quanxian <quanxian.wang@...el.com>
> > > > Link:
> > > > https://lore.kernel.org/linux-pm/53ec1f06f61c984100868926f282647e57ecfb2d.camel@intel.com/
> > > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > > > ---
> > > >  drivers/acpi/processor_thermal.c |   16 +++++++++++++---
> > > >  1 file changed, 13 insertions(+), 3 deletions(-)
> > > >
> > > > Index: linux-pm/drivers/acpi/processor_thermal.c
> > > > =================================================================
> > > > ==
> > > > --- linux-pm.orig/drivers/acpi/processor_thermal.c
> > > > +++ linux-pm/drivers/acpi/processor_thermal.c
> > > > @@ -140,9 +140,14 @@ void acpi_thermal_cpufreq_init(struct cp
> > > >               ret = freq_qos_add_request(&policy->constraints,
> > > >                                          &pr->thermal_req,
> > > >                                          FREQ_QOS_MAX, INT_MAX);
> > > > -             if (ret < 0)
> > > > +             if (ret < 0) {
> > > >                       pr_err("Failed to add freq constraint for
> > > > CPU%d
> > > > (%d)\n",
> > > >                              cpu, ret);
> > > > +                     continue;
> > > > +             }
> > > > +
> > > > +             if (!IS_ERR(pr->cdev))
> > > > +                     thermal_cooling_device_update(pr->cdev);
> > >
> > > Although thermal_cooling_device_update() handles "pr->cdev == NULL"
> > > case, I think it is better to use !IS_ERR_OR_NULL() here.
> >
> > Why is it?
> >
> > I was thinking about doing that, but then I realized that the NULL
> > case had been covered and that's why I went for the change above.  If
> > there is a particular reason to check for NULL here, I can do that,
> > but I'm not sure what it is.
>
> I don't have a strong objection here.
>
> I thought this was a code bug at first glance, until I double checked t
> hermal_cooling_device_update().
>
> So I think the latter would be more straight forward without
> introducing code complexity.

Alternatively, thermal_cooling_device_update() can be made to do the
full check instead.