linux-kernel - Re: [PATCH 0/1] power: supply: bq27xxx: expose battery data when CI=1

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Date:   Wed, 20 Apr 2022 00:09:59 +0200
From:   Pali Rohár <pali@...nel.org>
To:     "Sicelo A. Mhlongo" <absicsz@...il.com>
Cc:     sre@...nel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/1] power: supply: bq27xxx: expose battery data when CI=1

On Tuesday 19 April 2022 23:36:46 Sicelo A. Mhlongo wrote:
> We currently discard capacity information provided by the chip when the
> Capacity Inaccurate flag is set. However, in many cases, having this
> stale data is better than no information at all.
> 
> Even if the chip has been fully reset, the datasheet shows that capacity 
> values (NAC specifically) can be seeded by using the WRTNAC facility of 
> the Control and Mode registers. After seeding, CI remains set, but the
> capacity values are as accurate as the NAC value provided to WRTNAC is.

NAC (Nominal Available Capacity) is exported via CHARGE_NOW property.

So what about implementing CHARGE_NOW property also writable and write
operation would do this WRTNAC seeding? So userspace would be able to do
'echo new_value > charge_now' and for Nokia N900 case just directly
'cat .../rx51_battery/charge_full_design > .../bq27200/charge_now'

> On the Nokia N900, such seed value can be obtained from rx51_battery, 
> which reads battery data directly from the battery's BSI pin. This can
> be done in userspace via i2c access to the registers. With this patch,
> once seeded, capacity values are available through the driver.
> 
> The patch was successfully tested on bq27200 on the Nokia N900.
> 
> Signed-off-by: Sicelo A. Mhlongo <absicsz@...il.com>
> 
> Sicelo A. Mhlongo (1):
>   power: supply: bq27xxx: expose battery data when CI=1
> 
>  drivers/power/supply/bq27xxx_battery.c | 58 +++++++++++++-------------
>  1 file changed, 28 insertions(+), 30 deletions(-)
> 
> -- 
> 2.35.2
>