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SubjectRe: [PATCH v5 02/12] PM / devfreq: Fix handling of min/max_freq == 0
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Hi Matthias,

On 2018년 07월 07일 01:36, Matthias Kaehlcke wrote:
> 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.

I don't mind of 'soring order'. Thanks.

(snip)

--
Best Regards,
Chanwoo Choi
Samsung Electronics
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