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Message-ID: <20180706163624.GE129942@google.com>
Date: Fri, 6 Jul 2018 09:36:24 -0700
From: Matthias Kaehlcke <mka@...omium.org>
To: Chanwoo Choi <cw00.choi@...sung.com>
Cc: MyungJoo Ham <myungjoo.ham@...sung.com>,
Kyungmin Park <kyungmin.park@...sung.com>,
Arnd Bergmann <arnd@...db.de>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Rob Herring <robh+dt@...nel.org>,
Mark Rutland <mark.rutland@....com>, linux-pm@...r.kernel.org,
devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
Brian Norris <briannorris@...omium.org>,
Douglas Anderson <dianders@...omium.org>,
Enric Balletbo i Serra <enric.balletbo@...labora.com>,
"Rafael J . Wysocki" <rjw@...ysocki.net>,
Viresh Kumar <viresh.kumar@...aro.org>,
Lee Jones <lee.jones@...aro.org>,
Benson Leung <bleung@...omium.org>,
Olof Johansson <olof@...om.net>
Subject: Re: [PATCH v5 02/12] PM / devfreq: Fix handling of min/max_freq == 0
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@...omium.org>
> > Reviewed-by: Brian Norris <briannorris@...omium.org>
> > ---
> > Changes in v5:
> > - none
> >
> > Changes in v4:
> > - added 'Reviewed-by: Brian Norris <briannorris@...omium.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@...sung.com>
Thanks for the review!
Matthias
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