linux-kernel - Re: [PATCH 2/3] power: supply: cpcap-battery: Fix battery identification

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Date:   Tue, 15 Nov 2022 17:41:36 +0200
From:   Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>
To:     Tony Lindgren <tony@...mide.com>
Cc:     Sebastian Reichel <sebastian.reichel@...labora.com>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        philipp@...s.xyz, Pavel Machek <pavel@....cz>
Subject: Re: [PATCH 2/3] power: supply: cpcap-battery: Fix battery
 identification

Hi,

On 15.11.22 г. 15:49 ч., Tony Lindgren wrote:
> Hi,
> 
> * Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com> [221110 16:40]:
>> On 10.11.22 г. 18:05 ч., Sebastian Reichel wrote:
>>> Why do we care?
>>>
>> Because if we know the battery is genuine (or at least pretends to be :) ),
>> then we can read battery parameters from nvram, see patch 3/3. This will
>> allow us to charge HV LiPo batteries to 4.35V, using the full capacity.
> 
> Let's not enable charge voltages above 4.2V automatically at all unless
> the user chooses to set a higher charge voltage via sysfs manually.
> 
> We have had reports of bloated batteries if left connected to the charger
> at higher voltage than 4.2V. This seems to happen after connected for some
> weeks or months. AFAIK this happens both with Android and mainline kernel
> at higher voltages.
> 

Not that I sent such patch yet, but still, thinking about it, we should 
be able to easily prevent such damage by not restarting the charging 
after battery is full and voltage has dropped by 50mV or so. There can 
be a threshold (lets say 4.25 or 4.2) above which charging shall not be 
re-enabled unless the user reconnects the charger. Even if default stays 
4.2 and it is the user that has enabled 4.35. Just an idea.

> For more information, please see commit d4ee021c410f ("power: supply:
> cpcap-charger: Limit voltage to 4.2V for battery").
> 
> No objections for using the NVRAM to detect the battery max voltages
> though. That is as long as the default charge voltage does not go above
> 4.2V.

Patch 3/3 does just that - reads battery design parameters from NVRAM.

Regards,
Ivo

> 
> Regards,
> 
> Tony
>