Re: [External] Re: [PATCH 1/3] thinkpad_acpi: add support for force_discharge

From: Mark Pearson <markpearson@lenovo.com>
To: "Hans de Goede" <hdegoede@redhat.com>,
	"Thomas Koch" <linrunner@gmx.net>,
	"Nicolò Piazzalunga" <nicolopiazzalunga@gmail.com>,
	platform-driver-x86@vger.kernel.org,
	"Nitin Joshi1" <njoshi1@lenovo.com>,
	"Sebastian Reichel" <sre@kernel.org>,
	"Bastien Nocera" <hadess@hadess.net>,
	"Benjamin Berg" <bberg@redhat.com>
Cc: <jwrdegoede@fedoraproject.org>, <smclt30p@gmail.com>
Subject: Re: [External] Re: [PATCH 1/3] thinkpad_acpi: add support for force_discharge
Date: Wed, 29 Sep 2021 09:45:45 -0400	[thread overview]
Message-ID: <8c91bc0a-1701-ec01-3bec-3a520891c45c@lenovo.com> (raw)
In-Reply-To: <d486c621-2464-8763-553b-3543d0578b58@redhat.com>

On 2021-09-29 06:56, Hans de Goede wrote:
> Hi,
> 
> On 9/29/21 12:45 PM, Thomas Koch wrote:
>> Hi Hans,
>>
>>
>> On 29.09.21 11:55, Hans de Goede wrote:
>>
>>> Hi,
>>
>>>
>>
>>> On 9/29/21 7:47 AM, Thomas Koch wrote:
>>
>>>> Hi Hans,
>>
>>>>
>>
>>>> On 27.09.21 17:12, Hans de Goede wrote:
>>
>>>>> Hi Nicolò,
>>
>>>>>
>>
>>>>> On 9/27/21 5:00 PM, Nicolò Piazzalunga wrote:
>>
>>>>>> Hi,
>>
>>>>>>
>>
>>>>>> On 9/27/21 3:59 PM, Mark Pearson wrote:
>>
>>>>>>> Do let me know if there are some important use cases for these so
>> I can go back to the FW team and discuss supporting them properly.
>>
>>>>>>
>>
>>>>>> The important use cases are force discharge and inhibit charge.
>>
>>>>>> These at present are dealt with using tpacpi-bat, which relies on
>> (out of tree) acpi_call.
>>
>>>>>> See also your previous reply.
>>
>>>>>
>>
>>>>> I can see how those can be useful in certain circumstances.
>>
>>>>>
>>
>>>>> I can also understand how Lenovo does not want these to be
>>
>>>>> available by default everywhere.
>>
>>>>>
>>
>>>>> I think a good compromise would be to add a bool module option
>>
>>>>> which defaults to false to enable these.
>>
>>>>
>>
>>>>    From the user perspective, I don't agree that this is a good
>>
>>>> compromise. Users simply want to recalibrate their battery.
>>
>>>
>>
>>> But can't they already do this by just unplugging the AC and
>>
>>> then let the machine die ?Of course, but who wants that?
>>
>>> How is this different, does it somehow magically flicks on the
>>
>>> AC just before the battery deep-discharge protection kicks in
>>
>>> so no unsaved work is lost ?
>>
>> But this is exactly how it works. There is no risk of data loss.
>>
>>
>>
>> The EC resets the force_discharge flag at the end of the discharge and
>> the ThinkPad is seamlessly switched back to AC power. Just magical. No
>> power interruptions.
> 
> Interesting. So what I get from this is that we really only want
> force_discharge support. At least that is the major one. So maybe
> we should focus on just that one.
> 
> Anyways lets wait and see what Mark has to say about this. As
> I mentioned before doing battery calibration certainly is something
> which is desirable to do under Windows too, so perhaps this option
> is actually fine and it was the other 2 which are more
> "testing only" firmware features.
> 
> Regards,
> 
> Hans
> 
Hi,

I don't personally have any insight - I'm going to have to get feedback 
from the FW team on this. This is all new to me.

Thomas - thanks for the insight into how it is used. That will be really 
helpful to explain what we're looking for. As Hans mentioned we have an 
exercise to try and improve some of the battery related pieces for our 
platforms (largely driven by the TCO 9.0 requirements where I'm happy 
that the product teams are thinking of Linux before the fact rather than 
after) Battery calibration wasn't one of the things on my list, but it 
sounds interesting and useful. I don't think we have it in Windows - but 
I'm guessing and will confirm.
I also don't have any insight into how/why this was implemented on the 
older Thinkpads I'm afraid.

There was a follow up comment made from the FW team that there may be 
conditions where setting this may conflict with what the EC firmware is 
doing, so it will fail. It sounded like a corner-case to me but I don't 
have the details so I'll need to understand any concerns and go from there

Mark