Re: [External] Re: [RFC] ACPI: platform-profile: support for AC vs DC modes

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 3/14/22 15:59, Mark Pearson wrote:
> 
> Hi Hans & Mario
> 
> Thanks for all the comments.
> 
> On 2022-03-14 10:43, Hans de Goede wrote:
>> Hi Mario,
>>
>> On 3/14/22 14:39, Limonciello, Mario wrote:
>>> [Public]
>>>
>>>>>
>>>>> I cycled through a few different implementations but came down on what I
>>>>> proposed. I considered 6 values - but I don't think that makes sense and
>>>>> makes it overall more complicated than it needs to be and less flexible.
>>>>
>>>> Ah, so to be clear, my 2 scenarios above were theoretical scenarios,
>>>> because I'm wondering how the firmware API here actually looks like,
>>>> something which so far is not really clear to me.
>>>>
>>>> When you say that you considered using 6 values, then I guess that
>>>> the firmware API actually offers 6 values which we can write to a single slot:
>>>> ac-low-power,dc-lowpower,ac-balanced,dc-balanced,ac-performance,dc-
>>>> performance
>>>>
>>>> ?
>>>>
>>>> But that is not what the RFC patch that started this thread shows at all,
>>>> the API to the driver is totally unchanged and does not get passed
>>>> any info on ac/dc selection ?  So it seems to me that the ACPI API Linux
>>>> uses for this writes only 1 of 3 values to a single slot and the EC automatically
>>>> switches between say ac-balanced and dc-balanced internally.
>>>>
>>>> IOW there really being 2 differently tuned balance-profiles is not visible to
>>>> the OS at all, this is handled internally inside the EC, correct ?
>>>>
>>>
>>> No - on Lenovo's platform there are 6 different profiles that can be selected
>>> from the kernel driver.  3 are intended for use on battery, 3 are intended for
>>> use on AC.
>>
>> Ah, I already got that feeling from the rest of the thread, so I reread
>> Mark's RFC again before posting my reply today and the RFC looked like
>> the same 3 profiles were being set and the only functionality added
>> was auto profile switching when changing between AC/battery.
>>
>> Thank you for clarifying this. Having 6 different stories
>> indeed is a very different story.
> 
> Apologies if I wasn't clear. I was trying to come up with a design that
> took advantage of the AMD platforms have 6 settings, but was extensible
> generally to other situations.
> 
> I will redo the patches and add the thinkpad_acpi on top - that will
> help it be clearer.
>>
>>>> Otherwise I would expect the kernel internal driver API to also change and
>>>> to also see a matching thinkpad_acpi patch in the RFC series?
>>>
>>> The idea I see from Mark's thread was to send out RFC change for the platform profile
>>> and based on the direction try to implement the thinkpad-acpi change after that.
>>>
>>> Because of the confusion @Mark I think you should send out an RFC v2 with thinkpad acpi
>>> modeled on top of this the way that you want.
>>
>> I fully agree and since you introduce the concept of being on AC/battery to the
>> drivers/acpi/platform_profile.c cpde, please change the 
>> profile_set and profile_get function prototypes in struct platform_profile_handler
>> to also take a "bool on_battery" extra argument and use that in the thinkpad
>> driver to select either the ac or the battery tuned low/balanced/performance 
>> profile.
> 
> OK - I was thinking that, but I also figured the thinkpad driver could
> get the power status directly so it was largely redundant (and saves churn
> on all the other platform profile drivers - there are quite a few now)

If we get the power-status in 2 places things could get out of sync, there
could be unexpected race conditions, etc. Better to do just do it in one
place and pass the result along.

>> And please also include an update to Documentation/ABI/testing/sysfs-platform_profile
>> in the next RFC.
> Absolutely - that was intended. My aim with this RFC was to get feedback
> on if it was acceptable or not, and if the design had to change. Really
> appreciate all the good points.
> 
>>
>> Also notice how I've tried to consistently use AC/battery in my last reply,
>> DC really is not a good term for "on battery". AC also is sort of dubious
>> for "connected to an external power-supply" but its use for that is sorta
>> common and it is nice and short.
>>
>> Sorry if this seems like bikeshedding, but using DC for "on battery" just
>> feels wrong to me.
> Ack - and I'm good with the suggestion.
> 
>>
>>
>>>>> The biggest use case I can think of is that a user wants performance
>>>>> when plugged in and power-save when unplugged; and they want that to
>>>>> happen automatically.
>>>>
>>>> Right, so this what I have understood all along and I'm not disagreeing
>>>> that this is a desirable feature, but it _does not belong in the kernel_!
>>>>
>>>> Also taking Mario's remark about the EC-firmware using differently
>>>> tuned balanced profiles based on ac vs dc, here is how I envision this
>>>> working:
>>>>
>>>> 1. Laptop is connected to charger
>>>> 2. EC notices this and:
>>>> 2.1 Internally switches from balanced-dc settings to balanced-ac settings
>>>> 2.2 Sends out an event about the laptop now being on AC, which the kernel
>>>>     picks up and then sends to userspace (this already happens)
>>>> 3. Userspace, e.g. power-profiles-daemon, gets the event that the laptop is
>>>>    now an AC and in its settings sees that the user wants to switch to
>>>>    performance mode on AC and uses the platform_api in its current form to
>>>>    ask for a switch to performance mode
>>>> 4. The EC gets a command telling it to switch to performance mode and
>>>>    switches to the ac-tuned version of performance mode since the laptop is
>>>>    on ac.
>>>>
>>>
>>> None of this happens internally on the EC.
>>
>> Ack, I understand now thank you for clarifying this.
> Sorry for not being clear here
> 
>>
>>> Also there is nothing in this design
>>> that guarantees it needs to be EC driven profile changes.  It could be other
>>> mailboxes, ASL code, SMM etc.
>>>
>>> The key point here is that thinkpad acpi has 3 AC and 3 DC profiles to choose from,
>>> so some level from thinkpad acpi above needs to pick among them.
>>
>> Ack.
>>
> I think this is what makes having the design in the kernel more important.
> 
> I understand the keeping the kernel small, but the thinkpad_acpi driver
> needs to guarantee it knows it will get the notification. Without that I
> don't think I can implement the feature reliably
> 
> An alternative to the implementation is for me to do this in just the
> thinkpad_acpi driver and just for PSC mode, and that's what I started
> with when I looked at this (it's quite a nice simple implementation FWIW).
> But I figured having something that was configurable has benefits, and
> something that is applicable to all platforms is a nice feature as well.
> 
> If doing thinkpad_acpi only would be preferred and more acceptable let
> me know - but I think it's more limiting overall

I believe that given the hardware interface it makes sense to handle this
in the kernel; and for other platforms this will also give the option
to have 2 separate profiles for ac/battery and have the kernel auto-switch,
and they can just ignore the extra bool on_battery parameter to the
getters/setters.

Note we do still eventually need to get Rafael to weigh in and get
his consent on this too.

Regards,

Hans