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Date:   Fri, 6 Jul 2018 09:36:24 -0700
From:   Matthias Kaehlcke <mka@chromium.org>
To:     Chanwoo Choi <cw00.choi@samsung.com>
Cc:     MyungJoo Ham <myungjoo.ham@samsung.com>,
        Kyungmin Park <kyungmin.park@samsung.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>, linux-pm@vger.kernel.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        Brian Norris <briannorris@chromium.org>,
        Douglas Anderson <dianders@chromium.org>,
        Enric Balletbo i Serra <enric.balletbo@collabora.com>,
        "Rafael J . Wysocki" <rjw@rjwysocki.net>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Lee Jones <lee.jones@linaro.org>,
        Benson Leung <bleung@chromium.org>,
        Olof Johansson <olof@lixom.net>
Subject: Re: [PATCH v5 02/12] PM / devfreq: Fix handling of min/max_freq == 0
Message-ID: <20180706163624.GE129942@google.com>
References: <20180703234705.227473-1-mka@chromium.org>
 <CGME20180703235032epcas3p3443729f2230e205f1a0a4b03e6e8f62b@epcas3p3.samsung.com>
 <20180703234705.227473-3-mka@chromium.org>
 <5B3C2EEF.4080309@samsung.com>
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Hi Chanwoo,

On Wed, Jul 04, 2018 at 11:20:31AM +0900, Chanwoo Choi wrote:
> Hi Matthias,
> 
> On 2018년 07월 04일 08:46, Matthias Kaehlcke wrote:
> > Commit ab8f58ad72c4 ("PM / devfreq: Set min/max_freq when adding the
> > devfreq device") initializes df->min/max_freq with the min/max OPP when
> > the device is added. Later commit f1d981eaecf8 ("PM / devfreq: Use the
> > available min/max frequency") adds df->scaling_min/max_freq and the
> > following to the frequency adjustment code:
> > 
> >   max_freq = MIN(devfreq->scaling_max_freq, devfreq->max_freq);
> > 
> > With the current handling of min/max_freq this is incorrect:
> > 
> > Even though df->max_freq is now initialized to a value != 0 user space
> > can still set it to 0, in this case max_freq would be 0 instead of
> > df->scaling_max_freq as intended. In consequence the frequency adjustment
> > is not performed:
> > 
> >   if (max_freq && freq > max_freq) {
> > 	freq = max_freq;
> > 
> > To fix this set df->min/max freq to the min/max OPP in max/max_freq_store,
> > when the user passes a value of 0. This also prevents df->max_freq from
> > being set below the min OPP when df->min_freq is 0, and similar for
> > min_freq. Since it is now guaranteed that df->min/max_freq can't be 0 the
> > checks for this case can be removed.
> > 
> > Fixes: f1d981eaecf8 ("PM / devfreq: Use the available min/max frequency")
> > Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> > Reviewed-by: Brian Norris <briannorris@chromium.org>
> > ---
> > Changes in v5:
> > - none
> > 
> > Changes in v4:
> > - added 'Reviewed-by: Brian Norris <briannorris@chromium.org>' tag
> > 
> > Changes in v3:
> > - none
> > 
> > Changes in v2:
> > - handle freq tables sorted in ascending and descending order in
> >   min/max_freq_store()
> > - use same order for conditional statements in min/max_freq_store()
> > ---
> >  drivers/devfreq/devfreq.c | 42 ++++++++++++++++++++++++++++-----------
> >  1 file changed, 30 insertions(+), 12 deletions(-)
> > 
> > diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> > index 0057ef5b0a98..6f604f8b2b81 100644
> > --- a/drivers/devfreq/devfreq.c
> > +++ b/drivers/devfreq/devfreq.c
> > @@ -283,11 +283,11 @@ int update_devfreq(struct devfreq *devfreq)
> >  	max_freq = MIN(devfreq->scaling_max_freq, devfreq->max_freq);
> >  	min_freq = MAX(devfreq->scaling_min_freq, devfreq->min_freq);
> >  
> > -	if (min_freq && freq < min_freq) {
> > +	if (freq < min_freq) {
> >  		freq = min_freq;
> >  		flags &= ~DEVFREQ_FLAG_LEAST_UPPER_BOUND; /* Use GLB */
> >  	}
> > -	if (max_freq && freq > max_freq) {
> > +	if (freq > max_freq) {
> >  		freq = max_freq;
> >  		flags |= DEVFREQ_FLAG_LEAST_UPPER_BOUND; /* Use LUB */
> >  	}
> > @@ -1122,18 +1122,27 @@ static ssize_t min_freq_store(struct device *dev, struct device_attribute *attr,
> >  {
> >  	struct devfreq *df = to_devfreq(dev);
> >  	unsigned long value;
> > +	unsigned long *freq_table;
> 
> You can move 'freq_table' under 'else' statement.

Will do

> >  	int ret;
> > -	unsigned long max;
> >  
> >  	ret = sscanf(buf, "%lu", &value);
> >  	if (ret != 1)
> >  		return -EINVAL;
> >  
> >  	mutex_lock(&df->lock);
> > -	max = df->max_freq;
> > -	if (value && max && value > max) {
> > -		ret = -EINVAL;
> > -		goto unlock;
> > +
> > +	if (value) {
> > +		if (value > df->max_freq) {
> > +			ret = -EINVAL;
> > +			goto unlock;
> > +		}
> > +	} else {
> > +		freq_table = df->profile->freq_table;
> > +		/* typical order is ascending, some drivers use descending */
> 
> You better to explain what is doing of following code.
> How about modifying it as following?
> 
> 		/* Get minimum frequency according to sorting way */

Ok, will slightly modify it to 'sorting order' if you don't mind.

> > +		if (freq_table[0] < freq_table[df->profile->max_state - 1])
> > +			value = freq_table[0];
> > +		else
> > +			value = freq_table[df->profile->max_state - 1];
> >  	}
> >  
> >  	df->min_freq = value;
> > @@ -1157,18 +1166,27 @@ static ssize_t max_freq_store(struct device *dev, struct device_attribute *attr,
> >  {
> >  	struct devfreq *df = to_devfreq(dev);
> >  	unsigned long value;
> > +	unsigned long *freq_table;
> 
> ditto. You can move 'freq_table' under 'else' statement.

Will do

> >  	int ret;
> > -	unsigned long min;
> >  
> >  	ret = sscanf(buf, "%lu", &value);
> >  	if (ret != 1)
> >  		return -EINVAL;
> >  
> >  	mutex_lock(&df->lock);
> > -	min = df->min_freq;
> > -	if (value && min && value < min) {
> > -		ret = -EINVAL;
> > -		goto unlock;
> > +
> > +	if (value) {
> > +		if (value < df->min_freq) {
> > +			ret = -EINVAL;
> > +			goto unlock;
> > +		}
> > +	} else {
> > +		freq_table = df->profile->freq_table;
> > +		/* typical order is ascending, some drivers use descending */
> 
> ditto.
> 		/* Get maximum frequency according to sorting way */

Ok

> > +		if (freq_table[0] < freq_table[df->profile->max_state - 1])
> > +			value = freq_table[df->profile->max_state - 1];
> > +		else
> > +			value = freq_table[0];
> >  	}
> >  
> >  	df->max_freq = value;
> > 
> 
> If you agree my comment and modify this patch according to my comment,
> feel free to add my review tag.
> - Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>

Thanks for the review!

Matthias