Re: [PATCH v2] thermal:core:fix: Check return code of the ->get_max_state() callback

Eduardo Valentin
2014-11-24T18:02:18Z

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Hello Lukasz,

On Mon, Nov 24, 2014 at 11:38:54AM +0100, Lukasz Majewski wrote:
> Hi Eduardo,
>
> >
> > Lukasz,
> >
> > On Tue, Nov 18, 2014 at 11:16:30AM +0100, Lukasz Majewski wrote:
> > > The return code from ->get_max_state() callback was not checked
> > > during binding cooling device to thermal zone device.
> > >
> > > Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
> > > ---
> > > Changes for v2:
> > > - It turned out that patches from 1 to 6 from v1 are not needed,
> > > since they either already solve the problem (like imx_thermal.c) or
> > > not use cpufreq as a thermal cooling device.
> > > - The patch 7 from v1 is also not needed since this patch on error
> > > exits this function without using max_state variable.
> > > - In thermal driver probe the cpufreq_cooling_register() method
> > > presence is crucial to evaluate if the thermal driver needs any
> > > actions with -EPROBE_DEFER.
> >
> > Have you tried this patch with of-thermal based systems?
>
> Yes. I did try it with Exynos (after the rework). And there weren't
> any regressions.
>
> To be precise - do you refer to of_cpufreq_cooling_register() [1] or
> cpufreq_cooling_register() [2]?
>

[1]

> For the latter [2] - drivers like imx_thermal.c are fully prepared for
> -EDEFER_PROBE.
>
> For the former [1] - only cpufreq-dt.c uses it (and Exynos SoC after
> the rework).
>
> >
> > The above proposal works if the thermal driver is dealing with loading
> > cpu_cooling. But for of-thermal based drivers, the idea is to leave to
> > cpufreq code to load it.
>
> I assume, that you mean case [1]?
>

yup

> >
> > As an example, I am taking the ti-soc-thermal, but we already have
> > other of-thermal based drivers. Booting with this patch ti-soc-thermal
> > (of-based boot) loads fine, but the cpu_cooling never gets bound to
> > the thermal zone.
>
> Could you share the exact SoC/board/_defconfig setup to reproduce this
> behavior? I possess Beagle Bone Black, but it doesn't have thermal
> support (perhaps because its lack of accuracy).
>

Well, it may happen any system a driver with of-thermal + cpufreq-dt.

One board that is easily available is OMAP4460 panda board (tried
myself, the problem is there).

> With my Exynos setup I didn't experience any problems with this patch.
>
> >
> > The thing is that the bind may happen before cpufreq-dt code loads the
> > cpufreq driver, and when cpu_cooling is checking what is the max freq,
> > by using cpufreq table, it won't be able to do it, as there is no
> > table.
>
> As I look into the cpufreq-dt.c driver - in the cpufreq_init()
> function, the call to of_cpufreq_cooling_register() is performed just
> before cpufreq_table_validate_and_show().
> It looks like a mistake in the cpufreq-dt.c code.
>

Well, I believe for our case, better would be if the cpu_cooling could
be done after cpufreq driver registration call.

> >
> > While, without the patch, it will use wrong in the binding, but after
> > it gets bound, and cpufreq loads, the max will be used correctly.
>
> Correct. Such _wrong_ behavior was the original motivation to prepare
> this patch.
>
> >
> > And in this case, the system still works besides this bug.
>
> Unfortunately there is also a "window" in which the driver is not
> properly configured and can cause system crash, although it is unlikely.
>

Agreed.

>
> > The
> > reasoning is because the max state comes from DT (2) and lower and
> > upper wont be equal to THERMAL_NO_LIMIT. Then, the following check
> > will use the parameter, instead of max_state:
> >
> > cdev->ops->get_max_state(cdev, &max_state);
> >
> > /* lower default 0, upper default max_state */
> > lower = lower == THERMAL_NO_LIMIT ? 0 : lower;
> > upper = upper == THERMAL_NO_LIMIT ?
> > max_state : upper;
> >
> > In summary, introducing this patch, although it fix a problem, will
> > introduce regressions, in of-thermal based drivers.
>
> To be more precise - it will affect systems, which use of-thermal.c and
> cpufreq-dt.c in the same time, due to wrong ordering in the latter file.
>

Exactly.

> Could you give me a hint about the exact affected system? I've grep'ed
> for CPUFREQ_DT in the ./arch/arm/configs with no success.
>

Yeah, the grepping is correct. But well, just because it is not in
defconfigs does not mean it won't be used.

> >
> > I believe, to have this fix, you need to provide a way to have probing
> > deferring also in cpu_cooling. That needs also the change in the
> > cpufreq driver, as I mentioned in the other thread.
>
> I will think about possible solution and refer to previous discussion.
>

Good. For your patch, it is still sane to have it. But needs to be taken
after fixing the ordering between cpufreq-dt and cpu_cooling.

> >
> > Cheers,
> >
> > > ---
> > > drivers/thermal/thermal_core.c | 6 ++++--
> > > 1 file changed, 4 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/thermal/thermal_core.c
> > > b/drivers/thermal/thermal_core.c index 43b9070..8567929 100644
> > > --- a/drivers/thermal/thermal_core.c
> > > +++ b/drivers/thermal/thermal_core.c
> > > @@ -928,7 +928,7 @@ int thermal_zone_bind_cooling_device(struct
> > > thermal_zone_device *tz, struct thermal_zone_device *pos1;
> > > struct thermal_cooling_device *pos2;
> > > unsigned long max_state;
> > > - int result;
> > > + int result, ret;
> > >
> > > if (trip >= tz->trips || (trip < 0 && trip !=
> > > THERMAL_TRIPS_NONE)) return -EINVAL;
> > > @@ -945,7 +945,9 @@ int thermal_zone_bind_cooling_device(struct
> > > thermal_zone_device *tz, if (tz != pos1 || cdev != pos2)
> > > return -EINVAL;
> > >
> > > - cdev->ops->get_max_state(cdev, &max_state);
> > > + ret = cdev->ops->get_max_state(cdev, &max_state);
> > > + if (ret)
> > > + return ret;
> > >
> > > /* lower default 0, upper default max_state */
> > > lower = lower == THERMAL_NO_LIMIT ? 0 : lower;
> > > --
> > > 2.0.0.rc2
> > >
>
>
> --
> Best regards,
>
> Lukasz Majewski
>
> Samsung R&D Institute Poland (SRPOL) | Linux Platform Group

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