linux-kernel - Re: weird cooling_device/cur

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Message-ID: <20200321094321.6taz2d3fbkeo535i@macmini.local>
Date:   Sat, 21 Mar 2020 09:43:21 +0000
From:   Willy Wolff <willy.mh.wolff.ml@...il.com>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     Zhang Rui <rui.zhang@...el.com>,
        Eduardo Valentin <edubezval@...il.com>,
        Amit Kucheria <amit.kucheria@...durent.com>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: weird cooling_device/cur_state sysfs behaviour

Indeed, many thanks for you help.

On Fri, Mar 20, 2020 at 09:17:47pm +0100, Daniel Lezcano wrote:
> Adding Rafael,
> 
> On 20/03/2020 18:43, Daniel Lezcano wrote:
> > On 20/03/2020 16:10, Willy Wolff wrote:
> >> Hi all,
> >> Hope you're doing well with the situation.
> >>
> >> I fill that my board get a cold too...
> >>
> >> When I write to a sysfs node, I have a weird behaviour about the function that is called behind.
> >> This bug appears on an arm32 odroid-xu3, and only after v5.4, v5.3.18 behave correctly.
> >>
> >>
> >> Here my modification to see what's going on:
> >>
> >> diff --git a/drivers/thermal/thermal_sysfs.c b/drivers/thermal/thermal_sysfs.c
> >> index aa99edb4dff7..a437ae3f4b9f 100644
> >> --- a/drivers/thermal/thermal_sysfs.c
> >> +++ b/drivers/thermal/thermal_sysfs.c
> >> @@ -706,11 +706,22 @@ cur_state_store(struct device *dev, struct device_attribute *attr,
> > 
> > [ ... ]
> > 
> >>         return result ? result : count;
> >>  }
> >>  
> >> +
> > 
> > [ ... ]
> > 
> >>
> >> As you can see, the function is recalled with one character less, until the "buffer is empty".
> >> I don't understand why. Can anybody help me for this thing?
> >> Many thanks in advance.
> > 
> > [ ... ]
> > 
> > Very likely the problem is coming from:
> > 
> >         result = cdev->ops->set_cur_state(cdev, state);
> > 
> > which returns '1' as showed by the traces:
> > 
> > drivers/thermal/thermal_sysfs.c:735:cur_state_store result = 1, count = 3
> > 
> > And because of the return condition above:
> > 
> > 	return result ? result : count;
> > 
> >  the function is returning result, so '1', which is interpreted by the
> > sysfs as "I wrote one character', so it recalls the function with the
> > two remaining characters, etc ...
> > 
> > The problem is from the governor AFAICT, which governor is it?
> 
> I went through the code and I believe the problem is coming from:
> 
> cpufreq_set_cur_state
>  -> freq_qos_update_request
>    -> freq_qos_apply
>        -> pm_qos_update_target =>
> 
> " * This function returns 1 if the aggregated constraint value has changed,"
> 
> 	freq_qos_apply() does:
> 
> 		ret = pm_qos_update_target()
> 	...
> 	return ret;
> 
> 
> At the first glance, it is related to commit 77751a466ebd1 (Nov 2019).
> 
> 
> 
> 
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