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

From: Thomas Koch <linrunner@gmx.net>
To: Hans de Goede <hdegoede@redhat.com>, Sebastian Reichel <sre@kernel.org>
Cc: "Nicolo' Piazzalunga" <nicolopiazzalunga@gmail.com>,
	"platform-driver-x86@vger.kernel.org"
	<platform-driver-x86@vger.kernel.org>,
	"Mark Pearson" <markpearson@lenovo.com>,
	"Nitin Joshi1" <njoshi1@lenovo.com>,
	"jwrdegoede@fedoraproject.org" <jwrdegoede@fedoraproject.org>,
	"smclt30p@gmail.com" <smclt30p@gmail.com>,
	"Barnabás Pőcze" <pobrn@protonmail.com>
Subject: Re: [PATCH 1/3] thinkpad_acpi: add support for force_discharge
Date: Sat, 17 Apr 2021 13:49:46 +0200	[thread overview]
Message-ID: <a2d850e9-789d-54e8-e098-1a0829504031@gmx.net> (raw)
In-Reply-To: <6f58903f-5219-9aff-78ca-33687e2e4147@redhat.com>

Hi Hans,

from a userspace perspective, I don't think it's optimal to combine the
two features and the status. For example, how do I find out which one is
available?

I have to test the writability of status and then still don't know which
one is available. Seeing if force_discharge or inhibit_charge are there
is much simpler.

And then enabling that: triggering force_discharge by writing
"Discharging" is ok. But for inhibit_charge we would need a new status,
something like "Charging inhibited". This then causes problems for the
existing userspace, says: upowerd could not handle it. You remember the
"Not charging" patch from Ognen?

--

Freundliche Grüße / Kind regards,

Thomas Koch

Mail : linrunner@gmx.net

Web  : https://linrunner.de/tlp

On 13.04.21 10:05, Hans de Goede wrote:
> Hi,
>
> On 4/9/21 8:33 PM, Thomas Koch wrote:
>> Hi,
>>
>> On 08.04.21 15:51, Sebastian Reichel wrote:
>>
>>> IIUIC you have 'force_discharge', which basically means the system
>>> is running from battery power despite an AC adapter being connected
>>> and 'inhibit_discharge', which inhibits charging, so system does not
>>> charge battery when AC is connected, but uses AC to supply itself
>>> (so battery is idle)?
>>>
>>> We already have this kind of features on embedded systems (which
>>> often provide all kind of charger details). Those drivers solve
>>> this by having a writable 'status' property in the charger device:
>>>
>>> What:           /sys/class/power_supply/<supply_name>/status
>>> Date:           May 2007
>>> Contact:        linux-pm@vger.kernel.org
>>> Description:
>>>                   Represents the charging status of the battery. Normally this
>>>                   is read-only reporting although for some supplies this can be
>>>                   used to enable/disable charging to the battery.
>>>
>>>                   Access: Read, Write
>>>
>>>                   Valid values:
>>>                                 "Unknown", "Charging", "Discharging",
>>>                                 "Not charging", "Full"
>>>
>>> If I do not miss anything writing "Discharging" is the same as forced
>>> discharge and "Not Charging" (AKA Idle) is the same as your inhibit feature.
>>
>> There are ThinkPads with two batteries (BAT0, BAT1) and the hardware
>> allows to select which one to discharge. An approach through
>> /sys/class/power_supply/AC/status won't cover this.
>
> The mentioned status strings come from /sys/class/power_supply/VAT#/status,
> rather then from /sys/class/power_supply/AC/status.
>
> There is one problem though, which is that the status attribute is being
> managed by drivers/acpi/battery.c. There is infra for a driver like
> the thinkpad_apci driver to add new attributes to a power_supply but
> AFAIK there is no infra to say intercept writes to an attribute where
> the reading is handled by another driver.
>
> I guess we could add some special hook to allow another driver to
> intercept status writes.
>
> Sebastian, what is your take on this ?
>
> Regards,
>
> Hans
>