linux-kernel - Re: [PATCH 3/3] thermal: core: fix: Check return code of the ->get_max

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Message-id: <20141003124054.404ac26c@amdc2363>
Date:	Fri, 03 Oct 2014 12:40:54 +0200
From:	Lukasz Majewski <l.majewski@...sung.com>
To:	Eduardo Valentin <edubezval@...il.com>,
	Zhang Rui <rui.zhang@...el.com>
Cc:	Linux PM list <linux-pm@...r.kernel.org>,
	Lukasz Majewski <l.majewski@...ess.pl>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] thermal: core: fix: Check return code of the
 ->get_max_state() callback

Hi Eduardo, Rui,

> On Wed, Sep 24, 2014 at 10:27:12AM +0200, Lukasz Majewski wrote:
> > Without this check it was possible to execute cooling device
> > binding code even when wrong max cooling state was read.
> > 
> > Signed-off-by: Lukasz Majewski <l.majewski@...sung.com>
> 
> Acked-by: Eduardo Valentin <edubezval@...il.com>
> 
> Rui, are you taking these patches? Do you prefer me to collect them?

I'd like to ask you NOT to apply those patches.

In short: It will cause regression on all non Exynos boards.

Explanation:

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 properly
configured.

Applying PATCH2/3 and PATCH3/3 would cause bind error without any
further occasion for re-bind. As a result THERAL will not be present
on the target system.

It works on the Exynos boards, since at the report_trigger() function, 
when first trip point is reached, it is checked if cpu_cooling device
is bind. If it is not (due to "fixes" at PATCH2/3 and PATCH3/3) it
is rebind then.

Due to above, I think that it would be best to leave things as they are
now and prepare proper fix as suggested by Eduardo.

> 
> Cheers
> 
> Eduardo
> 
> > ---
> >  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 747618a..8a4dc35 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 = 0;
> > -	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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