Messages in this thread | | | Date | Mon, 6 Oct 2014 14:01:13 -0400 | From | Eduardo Valentin <> | Subject | Re: [PATCH 2/3] thermal: core: fix: Initialize the max_state variable to 0 |
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On Fri, Oct 03, 2014 at 10:26:28AM +0200, Lukasz Majewski wrote: > Hi Eduardo, > > > Hello Lukasz, > > > > On Wed, Sep 24, 2014 at 10:27:11AM +0200, Lukasz Majewski wrote: > > > Pointer to the uninitialized max_state variable is passed to get the > > > maximal cooling state. > > > For CPU cooling device (cpu_cooling.c) the cpufreq_get_max_state() > > > is called, which even when error occurs will return the max_state > > > variable unchanged. > > > Since error for ->get_max_state() is not checked, the automatically > > > > > > Good that you added a fix in your series for this. > > > > > > > allocated value of max_state is used for (upper > max_state) > > > comparison. For any possible max_state value it is very unlikely > > > that it will be less than upper. > > > As a consequence, the cooling device is bind even without the backed > > > cpufreq table initialized. > > > > > > This initialization will prevent from accidental binding trip > > > points to cpu freq cooling frequencies when cpufreq driver itself > > > is not yet fully initialized. > > > > Although I agree with the fix, as long as we also include a check for > > the .get_max_state return value, I believe the problem you are > > describing is about initialization sequence. > > As you pointed out - the problem here is with initialization sequence. > Thermal and cpufreq cores are initialized very early. > > However, the get_max_state() for cpu_cooling.c device (as it is the > pervasive way of cooling things) accesses cpufreq policy to get the > freq_table and count available states. > > The issue here is with late initialization of cpufreq policy. > > Up till now the cpu_cooling device was bind even when the > get_max_state() returned -EINVAL and everything worked after late > cpufreq policy initialization. However, during this time window the > thermal driver is not configured. > > > > > In general, I believe we need a better > > sequencing between thermal and cpufreq subsystems. One way out is to > > include a check for cpufreq driver in the thermal driver, and return > > -EPROBE_DEFER when cpufreq is not ready. > > I think that we could return -EPROBE_DEFER when cpufreq's policy is not > yet available and subscribe to cpufreq notifier to call > bind_cooling_device then.
I agree with this approach, as long as we keep the existing users of cpufreq cooling in a working state.
Cheers
> > Let's wait for Zhang opinion since he looks after the thermal core code. > > > > > > > > > Signed-off-by: Lukasz Majewski <l.majewski@samsung.com> > > > --- > > > drivers/thermal/thermal_core.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/drivers/thermal/thermal_core.c > > > b/drivers/thermal/thermal_core.c index 454884a..747618a 100644 > > > --- a/drivers/thermal/thermal_core.c > > > +++ b/drivers/thermal/thermal_core.c > > > @@ -927,7 +927,7 @@ int thermal_zone_bind_cooling_device(struct > > > thermal_zone_device *tz, struct thermal_instance *pos; > > > struct thermal_zone_device *pos1; > > > struct thermal_cooling_device *pos2; > > > - unsigned long max_state; > > > + unsigned long max_state = 0; > > > int result; > > > > > > if (trip >= tz->trips || (trip < 0 && trip != > > > THERMAL_TRIPS_NONE)) -- > > > 2.0.0.rc2 > > > > > > > > > -- > Best regards, > > Lukasz Majewski > > Samsung R&D Institute Poland (SRPOL) | Linux Platform Group
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