On 2018년 07월 07일 02:53, Matthias Kaehlcke wrote:
> Hi Chanwoo,
> On Wed, Jul 04, 2018 at 03:41:46PM +0900, Chanwoo Choi wrote:
>> I'm not sure why devfreq needs the devfreq_verify_within_limits() function.
>> devfreq already used the OPP interface as default. It means that
>> the outside of 'drivers/devfreq' can disable/enable the frequency
>> such as drivers/thermal/devfreq_cooling.c. Also, when some device
>> drivers disable/enable the specific frequency, the devfreq core
>> consider them.
>> So, devfreq doesn't need to devfreq_verify_within_limits() because
>> already support some interface to change the minimum/maximum frequency
>> of devfreq device.
>> In case of cpufreq subsystem, cpufreq only provides
>> to change the minimum/maximum frequency of cpu. some device driver cannot
>> change the minimum/maximum frequency through OPP interface.
>> But, in case of devfreq subsystem, as I explained already, devfreq support
>> the OPP interface as default way. devfreq subsystem doesn't need to add
>> other way to change the minimum/maximum frequency.
> Using the OPP interface exclusively works as long as a
> enabling/disabling of OPPs is limited to a single driver
> (drivers/thermal/devfreq_cooling.c). When multiple drivers are
> involved you need a way to resolve conflicts, that's the purpose of
> devfreq_verify_within_limits(). Please let me know if there are
> existing mechanisms for conflict resolution that I overlooked.
> Possibly drivers/thermal/devfreq_cooling.c could be migrated to use
> devfreq_verify_within_limits() instead of the OPP interface if
> desired, however this seems beyond the scope of this series.
Actually, if we uses this approach, it doesn't support the multiple drivers too.
If non throttler drivers uses devfreq_verify_within_limits(), the conflict
To resolve the conflict for multiple device driver, maybe OPP interface
have to support 'usage_count' such as clk_enable/disable().
>> This patch send the 'struct devfreq_policy' instance as the data
>> when sending the notification as following:
>> DEVFREQ_ADJUST, policy);
>> But, I think that if devfreq core sends the 'struct devfreq_freq_limits'
>> instance instead of 'struct devfreq_policy', it is enough.
>> Because receiver of DEVFREQ_ADJUST just will use the min_freq/max_freq
>> So, I tried to find the cpufreq's case. The some device drivers using
>> CPUFREQ_POLICY_NOTIFIER uses following variables of 'struct cpufreq_policy'.
>> It means that receiver of CPUFREQ_POLICY_NOTIFIER don't need to other
>> information/variables except for min/max frequency.
>> - policy->min
>> - policy->max
>> - policy->cpuinfo.max_freq
>> - policy->cpuinfo.min_freq
>> - policy->cpu : not related to devfreq)
>> - policy->related_cpus : not related to devfreq)
>> - list of device drivers using CPUFREQ_POLICY_NOTIFIER (linux kernel is
>> $ grep -rn "CPUFREQ_POLICY_NOTIFIER" .
> Thanks for your investigation.
> I decided to mirror the cpufreq interface for consistency, but I agree
> that 'struct devfreq_freq_limits' could be passed instead of the
> policy object. I'm fine with changing that.
>> On 2018년 07월 04일 08:46, Matthias Kaehlcke wrote:
>>> Policy notifiers are called before a frequency change and may narrow
>>> the min/max frequency range in devfreq_policy, which is used to adjust
>>> the target frequency if it is beyond this range.
>>> Also add a few helpers:
>>> - devfreq_verify_within_[dev_]limits()
>>> - should be used by the notifiers for policy adjustments.
>>> - dev_to_devfreq()
>>> - lookup a devfreq strict from a device pointer
>>> Signed-off-by: Matthias Kaehlcke <m...@chromium.org>
>>> Reviewed-by: Brian Norris <briannor...@chromium.org>
>>> Changes in v5:
>>> - none
>>> Changes in v4:
>>> - Fixed typo in commit message: devfreg => devfreq
>>> - added 'Reviewed-by: Brian Norris <briannor...@chromium.org>' tag
>>> Changes in v3:
>>> - devfreq.h: fixed misspelling of struct devfreq_policy
>>> Changes in v2:
>>> - performance, powersave and simpleondemand governors don't need changes
>>> with "PM / devfreq: Don't adjust to user limits in governors"
>>> - formatting fixes
>>> drivers/devfreq/devfreq.c | 48 ++++++++++++++++++++++-------
>>> include/linux/devfreq.h | 65 +++++++++++++++++++++++++++++++++++++++
>>> 2 files changed, 102 insertions(+), 11 deletions(-)
>>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>>> index 21604d6ae2b8..4cbaa7ad1972 100644
>>> --- a/drivers/devfreq/devfreq.c
>>> +++ b/drivers/devfreq/devfreq.c
>>> @@ -72,6 +72,21 @@ static struct devfreq *find_device_devfreq(struct device
>>> return ERR_PTR(-ENODEV);
>>> + * dev_to_devfreq() - find devfreq struct using device pointer
>>> + * @dev: device pointer used to lookup device devfreq.
>>> + */
>>> +struct devfreq *dev_to_devfreq(struct device *dev)
>>> + struct devfreq *devfreq;
>>> + mutex_lock(&devfreq_list_lock);
>>> + devfreq = find_device_devfreq(dev);
>>> + mutex_unlock(&devfreq_list_lock);
>>> + return devfreq;
>>> static unsigned long find_available_min_freq(struct devfreq *devfreq)
>>> struct dev_pm_opp *opp;
>>> @@ -269,20 +284,21 @@ int update_devfreq(struct devfreq *devfreq)
>>> if (!policy->governor)
>>> return -EINVAL;
>>> + policy->min = policy->devinfo.min_freq;
>>> + policy->max = policy->devinfo.max_freq;
>> Why don't you consider 'policy->user.max/min_freq' as following?
>> As I already commented, I think that 'struct devfreq_freq_limits' is enough
>> instead of 'struct devfreq_policy'.
>> ->max_freq = MIN(policy->devinfo.max_freq, policy->user.max_freq);
>> ->min_freq = MAX(policy->devinfo.min_freq, policy->user.min_freq);
> You mean limiting the frequency range with user.min/max before
> DEVFREQ_ADJUST instead of adjusting it afterwards? That's fine with