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SubjectRe: [PATCH 1/2] PM / devfreq: add min/max_freq limit requested by users.
From
2012/1/12 Rafael J. Wysocki <rjw@sisk.pl>:
> On Wednesday, January 11, 2012, MyungJoo Ham wrote:
>> The frequency requested to devfreq device driver from devfreq governors
>> is restricted by min_freq and max_freq input.
>
> Can you please give us a bit more information about why this change is
> necessary or desirable?
>
> Rafael


During developing a device with DVFS capabilities on Memory-Interface,
Bus, and GPU, there have been needs for configuring min/max freuqency
at userspace (by either "platform software" or "command line inputs of
developers"):

1. (debugging/testing) Test whether a symptom is occurred by DVFS
mechanism setting the frequency too low.

2. Set minimum frequency of a specific device for a specific behavior
(e.g., set GPU >= 200MHz if it is playing 1080p video because if we
let DVFS handle without minimum, sometimes it goes lower than 200MHz
and up, which incurs flickering.). Because userspace often directly
access such devices (accessing device with memory allocated by
DRM+GEM), kernel device driver may not be able to get what's going on
easily. This will probably be handled by platform software.

3. Userspace (the platform such as Tizen, Android, or others) wants to
limit (max frequency) the usage when 1. it's too hot, or 2. the
battery level is low, especially for GPUs.

I guess these are what I've been experiencing with DVFS recently. For
kernel developers, 1. was the most significant anyway.


Cheers!
MyungJoo

>
>
>> Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>
>> Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
>> ---
>>  drivers/devfreq/devfreq.c                 |   70 +++++++++++++++++++++++++++++
>>  drivers/devfreq/governor_performance.c    |    5 ++-
>>  drivers/devfreq/governor_powersave.c      |    2 +-
>>  drivers/devfreq/governor_simpleondemand.c |   12 ++++-
>>  drivers/devfreq/governor_userspace.c      |   15 +++++-
>>  include/linux/devfreq.h                   |    5 ++
>>  6 files changed, 101 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>> index 59d24e9..358d129 100644
>> --- a/drivers/devfreq/devfreq.c
>> +++ b/drivers/devfreq/devfreq.c
>> @@ -502,12 +502,82 @@ static ssize_t show_central_polling(struct device *dev,
>>                      !to_devfreq(dev)->governor->no_central_polling);
>>  }
>>
>> +static ssize_t store_min_freq(struct device *dev, struct device_attribute *attr,
>> +                           const char *buf, size_t count)
>> +{
>> +     struct devfreq *df = to_devfreq(dev);
>> +     unsigned long value;
>> +     int ret;
>> +     unsigned long max;
>> +
>> +     ret = sscanf(buf, "%lu", &value);
>> +     if (ret != 1)
>> +             goto out;
>> +
>> +     mutex_lock(&df->lock);
>> +     max = df->max_freq;
>> +     if (value && max && value > max) {
>> +             ret = -EINVAL;
>> +             goto unlock;
>> +     }
>> +
>> +     df->min_freq = value;
>> +     update_devfreq(df);
>> +     ret = count;
>> +unlock:
>> +     mutex_unlock(&df->lock);
>> +out:
>> +     return ret;
>> +}
>> +
>> +static ssize_t show_min_freq(struct device *dev, struct device_attribute *attr,
>> +                          char *buf)
>> +{
>> +     return sprintf(buf, "%lu\n", to_devfreq(dev)->min_freq);
>> +}
>> +
>> +static ssize_t store_max_freq(struct device *dev, struct device_attribute *attr,
>> +                           const char *buf, size_t count)
>> +{
>> +     struct devfreq *df = to_devfreq(dev);
>> +     unsigned long value;
>> +     int ret;
>> +     unsigned long min;
>> +
>> +     ret = sscanf(buf, "%lu", &value);
>> +     if (ret != 1)
>> +             goto out;
>> +
>> +     mutex_lock(&df->lock);
>> +     min = df->min_freq;
>> +     if (value && min && value < min) {
>> +             ret = -EINVAL;
>> +             goto unlock;
>> +     }
>> +
>> +     df->max_freq = value;
>> +     update_devfreq(df);
>> +     ret = count;
>> +unlock:
>> +     mutex_unlock(&df->lock);
>> +out:
>> +     return ret;
>> +}
>> +
>> +static ssize_t show_max_freq(struct device *dev, struct device_attribute *attr,
>> +                          char *buf)
>> +{
>> +     return sprintf(buf, "%lu\n", to_devfreq(dev)->max_freq);
>> +}
>> +
>>  static struct device_attribute devfreq_attrs[] = {
>>       __ATTR(governor, S_IRUGO, show_governor, NULL),
>>       __ATTR(cur_freq, S_IRUGO, show_freq, NULL),
>>       __ATTR(central_polling, S_IRUGO, show_central_polling, NULL),
>>       __ATTR(polling_interval, S_IRUGO | S_IWUSR, show_polling_interval,
>>              store_polling_interval),
>> +     __ATTR(min_freq, S_IRUGO | S_IWUSR, show_min_freq, store_min_freq),
>> +     __ATTR(max_freq, S_IRUGO | S_IWUSR, show_max_freq, store_max_freq),
>>       { },
>>  };
>>
>> diff --git a/drivers/devfreq/governor_performance.c b/drivers/devfreq/governor_performance.c
>> index c0596b2..574a06b 100644
>> --- a/drivers/devfreq/governor_performance.c
>> +++ b/drivers/devfreq/governor_performance.c
>> @@ -18,7 +18,10 @@ static int devfreq_performance_func(struct devfreq *df,
>>        * target callback should be able to get floor value as
>>        * said in devfreq.h
>>        */
>> -     *freq = UINT_MAX;
>> +     if (!df->max_freq)
>> +             *freq = UINT_MAX;
>> +     else
>> +             *freq = df->max_freq;
>>       return 0;
>>  }
>>
>> diff --git a/drivers/devfreq/governor_powersave.c b/drivers/devfreq/governor_powersave.c
>> index 2483a85..d742d4a 100644
>> --- a/drivers/devfreq/governor_powersave.c
>> +++ b/drivers/devfreq/governor_powersave.c
>> @@ -18,7 +18,7 @@ static int devfreq_powersave_func(struct devfreq *df,
>>        * target callback should be able to get ceiling value as
>>        * said in devfreq.h
>>        */
>> -     *freq = 0;
>> +     *freq = df->min_freq;
>>       return 0;
>>  }
>>
>> diff --git a/drivers/devfreq/governor_simpleondemand.c b/drivers/devfreq/governor_simpleondemand.c
>> index efad8dc..a2e3eae 100644
>> --- a/drivers/devfreq/governor_simpleondemand.c
>> +++ b/drivers/devfreq/governor_simpleondemand.c
>> @@ -25,6 +25,7 @@ static int devfreq_simple_ondemand_func(struct devfreq *df,
>>       unsigned int dfso_upthreshold = DFSO_UPTHRESHOLD;
>>       unsigned int dfso_downdifferential = DFSO_DOWNDIFFERENCTIAL;
>>       struct devfreq_simple_ondemand_data *data = df->data;
>> +     unsigned long max = (df->max_freq) ? df->max_freq : UINT_MAX;
>>
>>       if (err)
>>               return err;
>> @@ -41,7 +42,7 @@ static int devfreq_simple_ondemand_func(struct devfreq *df,
>>
>>       /* Assume MAX if it is going to be divided by zero */
>>       if (stat.total_time == 0) {
>> -             *freq = UINT_MAX;
>> +             *freq = max;
>>               return 0;
>>       }
>>
>> @@ -54,13 +55,13 @@ static int devfreq_simple_ondemand_func(struct devfreq *df,
>>       /* Set MAX if it's busy enough */
>>       if (stat.busy_time * 100 >
>>           stat.total_time * dfso_upthreshold) {
>> -             *freq = UINT_MAX;
>> +             *freq = max;
>>               return 0;
>>       }
>>
>>       /* Set MAX if we do not know the initial frequency */
>>       if (stat.current_frequency == 0) {
>> -             *freq = UINT_MAX;
>> +             *freq = max;
>>               return 0;
>>       }
>>
>> @@ -79,6 +80,11 @@ static int devfreq_simple_ondemand_func(struct devfreq *df,
>>       b = div_u64(b, (dfso_upthreshold - dfso_downdifferential / 2));
>>       *freq = (unsigned long) b;
>>
>> +     if (df->min_freq && *freq < df->min_freq)
>> +             *freq = df->min_freq;
>> +     if (df->max_freq && *freq > df->max_freq)
>> +             *freq = df->max_freq;
>> +
>>       return 0;
>>  }
>>
>> diff --git a/drivers/devfreq/governor_userspace.c b/drivers/devfreq/governor_userspace.c
>> index 4f8b563..0681246 100644
>> --- a/drivers/devfreq/governor_userspace.c
>> +++ b/drivers/devfreq/governor_userspace.c
>> @@ -25,10 +25,19 @@ static int devfreq_userspace_func(struct devfreq *df, unsigned long *freq)
>>  {
>>       struct userspace_data *data = df->data;
>>
>> -     if (!data->valid)
>> +     if (data->valid) {
>> +             unsigned long adjusted_freq = data->user_frequency;
>> +
>> +             if (df->max_freq && adjusted_freq > df->max_freq)
>> +                     adjusted_freq = df->max_freq;
>> +
>> +             if (df->min_freq && adjusted_freq < df->min_freq)
>> +                     adjusted_freq = df->min_freq;
>> +
>> +             *freq = adjusted_freq;
>> +     } else {
>>               *freq = df->previous_freq; /* No user freq specified yet */
>> -     else
>> -             *freq = data->user_frequency;
>> +     }
>>       return 0;
>>  }
>>
>> diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
>> index 98ce812..e9385bf 100644
>> --- a/include/linux/devfreq.h
>> +++ b/include/linux/devfreq.h
>> @@ -124,6 +124,8 @@ struct devfreq_governor {
>>   *           touch this.
>>   * @being_removed    a flag to mark that this object is being removed in
>>   *                   order to prevent trying to remove the object multiple times.
>> + * @min_freq Limit minimum frequency requested by user (0: none)
>> + * @max_freq Limit maximum frequency requested by user (0: none)
>>   *
>>   * This structure stores the devfreq information for a give device.
>>   *
>> @@ -149,6 +151,9 @@ struct devfreq {
>>       void *data; /* private data for governors */
>>
>>       bool being_removed;
>> +
>> +     unsigned long min_freq;
>> +     unsigned long max_freq;
>>  };
>>
>>  #if defined(CONFIG_PM_DEVFREQ)
>>
>



--
MyungJoo Ham, Ph.D.
Mobile Software Platform Lab, DMC Business, Samsung Electronics
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