Date:   Mon, 13 Mar 2023 09:35:27 +0000
From:   Lukasz Luba <lukasz.luba@....com>
To:     Xuewen Yan <xuewen.yan94@...il.com>
Cc:     Di Shen <di.shen@...soc.com>, daniel.lezcano@...aro.org,
        rafael@...nel.org, amitk@...nel.org, rui.zhang@...el.com,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        xuewen.yan@...soc.com, Qais Yousef <qyousef@...alina.io>
Subject: Re: [PATCH] thermal/core/power_allocator: avoid cdev->state can not
 be reset

Hi Xuewen,

On 3/13/23 01:40, Xuewen Yan wrote:
> Hi Lukasz
> 
> On Fri, Mar 10, 2023 at 11:56 PM Lukasz Luba <lukasz.luba@....com> wrote:
>>
>> Hi Di,
>>
>> On 3/9/23 13:55, Di Shen wrote:
>>> Commit 0952177f2a1f (thermal/core/power_allocator: Update once cooling devices when temp is low)
>>> add a update flag to update cooling device only once when temp is low.
>>> But when the switch_on_temp is set to be a higher value, the cooling device state
>>> may not be reset to max, because the last_temp is smaller than the switch_on_temp.
>>>
>>> For example:
>>> First:
>>> swicth_on_temp=70 control_temp=85;
>>>
>>> Then userspace change the trip_temp:
>>> swicth_on_temp=45 control_temp=55 cur_temp=54
>>>
>>> Then userspace reset the trip_temp:
>>> swicth_on_temp=70 control_temp=85 cur_temp=57 last_temp=54
>>>
>>> At this time, the cooling device state should be reset to be max.
>>> However, because cur_temp(57) < switch_on_temp(70)
>>> last_temp(54) < swicth_on_temp(70) --> update = false
>>> When update is false, the cooling device state can not be reset.
>>
>> That's a tricky use case. How is that now possible,
> 
> We use the trip_temp in the Android System. Often, we set different
> control temperatures in different scenarios,
> and when we change the switch_on_temp from small to bigger, we find
> the power can not be reset to be max.

I see, thanks for letting me know that this is Android.

> 
> 
>>>
>>> So delete the update condition, so that the cooling device state
>>> could be reset.
>>
>> IMO this is not the desired solution. Daniel reported the issue that
>> IPA triggers the event sent to user-space even when there is no need.
>> That's the motivation for the 0952177f2a1f change.
>>
>> To address your scenario properly, we need an interface which allows
>> to respond properly for such situation when someone from user-space
>> writes a new value to something fundamental as trip point.
>>
>> You also have a kernel config enabled:
>> CONFIG_THERMAL_WRITABLE_TRIPS
>> which IMO is only for debug kernels for system integrator (according
>> to the Kconfig description).
> 
>   Yes, we use it to meet the temperature control needs of different scenarios.
> And now in android with google's GKI2.0, the config must be opened.

OK

> 
>>
>> When you disable this config in your deploy/product kernel
>> than this issue would disappear.
>>
>>>
>>> Fixes: 0952177f2a1f (thermal/core/power_allocator: Update once cooling devices when temp is low)
>>> Signed-off-by: Di Shen <di.shen@...soc.com>
>>> ---
>>>    drivers/thermal/gov_power_allocator.c | 9 +++------
>>>    1 file changed, 3 insertions(+), 6 deletions(-)
>>>
>>
>> That's why IMO this is not the solution.
> 
> Yes, but I think we should fix the bug, although the
> CONFIG_THERMAL_WRITABLE_TRIPS is just for debugging.
> How about record the last_trip_temp, and when the last_temp >
> last_trip_temp, set the update tobe true?

Yes, if that config is used in Android then we must fix it.

That last_trip_temp makes sense (but maybe name it last_switch_on_temp).
Please put that new field into the IPA local
struct power_allocator_params. We should store the trip temp
value there every time power_allocator_throttle() is called.
That can be called due to a write from user-space w/ a new trip point
value, so should be OK.

Regards,
Lukasz

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