linux-kernel - Re: [PATCH] sbs-battery: fix power status when battery is dry

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Message-ID: <56FBEC12.10705@nvidia.com>
Date:	Wed, 30 Mar 2016 11:09:06 -0400
From:	Rhyland Klein <rklein@...dia.com>
To:	YH Huang <yh.huang@...iatek.com>
CC:	Daniel Kurtz <djkurtz@...omium.org>, <linux-pm@...r.kernel.org>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	Sebastian Reichel <sre@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"moderated list:ARM/Mediatek SoC support" 
	<linux-mediatek@...ts.infradead.org>,
	Matthias Brugger <matthias.bgg@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] sbs-battery: fix power status when battery is dry

On 3/30/2016 4:58 AM, YH Huang wrote:
> On Tue, 2016-03-29 at 11:05 -0400, Rhyland Klein wrote:
>> On 3/28/2016 9:52 PM, YH Huang wrote:
>>> On Mon, 2016-03-28 at 11:57 -0400, Rhyland Klein wrote:
>>>> On 3/28/2016 6:05 AM, Daniel Kurtz wrote:
>>>>> +Rhyland Klein who original wrote this code...
>>>>>
>>>>> On Mon, Mar 28, 2016 at 10:32 AM, YH Huang <yh.huang@...iatek.com> wrote:
>>>>>>
>>>>>> On Fri, 2016-03-25 at 11:06 +0800, Daniel Kurtz wrote:
>>>>>>> On Thu, Mar 24, 2016 at 2:43 PM, YH Huang <yh.huang@...iatek.com> wrote:
>>>>>>>>
>>>>>>>> Hi Daniel,
>>>>>>>>
>>>>>>>> On Thu, 2016-03-24 at 12:01 +0800, Daniel Kurtz wrote:
>>>>>>>>> Hi YH,
>>>>>>>>>
>>>>>>>>> On Wed, Mar 23, 2016 at 5:53 PM, YH Huang <yh.huang@...iatek.com> wrote:
>>>>>>>>>> When the battery is dry and BATTERY_FULL_DISCHARGED is set,
>>>>>>>>>> we should check BATTERY_DISCHARGING to decide the power status.
>>>>>>>>>> If BATTERY_DISCHARGING is set, the power status is not charging.
>>>>>>>>>> Or the power status should be charging.
>>>>>>>>>>
>>>>>>>>>> Signed-off-by: YH Huang <yh.huang@...iatek.com>
>>>>>>>>>> ---
>>>>>>>>>>  drivers/power/sbs-battery.c |   22 ++++++++++++----------
>>>>>>>>>>  1 file changed, 12 insertions(+), 10 deletions(-)
>>>>>>>>>>
>>>>>>>>>> diff --git a/drivers/power/sbs-battery.c b/drivers/power/sbs-battery.c
>>>>>>>>>> index d6226d6..d86db0e 100644
>>>>>>>>>> --- a/drivers/power/sbs-battery.c
>>>>>>>>>> +++ b/drivers/power/sbs-battery.c
>>>>>>>>>> @@ -382,11 +382,12 @@ static int sbs_get_battery_property(struct i2c_client *client,
>>>>>>>>>>
>>>>>>>>>>                 if (ret & BATTERY_FULL_CHARGED)
>>>>>>>>>>                         val->intval = POWER_SUPPLY_STATUS_FULL;
>>>>>>>>>> -               else if (ret & BATTERY_FULL_DISCHARGED)
>>>>>>>>>> -                       val->intval = POWER_SUPPLY_STATUS_NOT_CHARGING;
>>>>>>>>>> -               else if (ret & BATTERY_DISCHARGING)
>>>>>>>>>> -                       val->intval = POWER_SUPPLY_STATUS_DISCHARGING;
>>>>>>>>>> -               else
>>>>>>>>>> +               else if (ret & BATTERY_DISCHARGING) {
>>>>>>>>>> +                       if (ret & BATTERY_FULL_DISCHARGED)
>>>>>>>>>> +                               val->intval = POWER_SUPPLY_STATUS_NOT_CHARGING;
>>>>>>>>>> +                       else
>>>>>>>>>> +                               val->intval = POWER_SUPPLY_STATUS_DISCHARGING;
>>>>>>>>>> +               } else
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> I think (BATTERY_DISCHARGING && BATTERY_FULL_DISCHARGED) is still
>>>>>>>>> POWER_SUPPLY_STATUS_DISCHARGING.
>>>>>>>>> So, let's just report what the battery says and do:
>>>>>>>>>
>>>>>>>>>                else if (ret & BATTERY_DISCHARGING)
>>>>>>>>>                                val->intval = POWER_SUPPLY_STATUS_DISCHARGING;
>>>>>>>>>
>>>>>>>> So we just ignore the special situation (BATTERY_DISCHARGING &&
>>>>>>>> BATTERY_FULL_DISCHARGED).
>>>>>>>> Isn't POWER_SUPPLY_STATUS_NOT_CHARGING a useful information?
>>>>>>>
>>>>>>> The battery is discharging.  The fact that it is also reporting that
>>>>>>> it is already "discharged" just seems premature.   I would expect to
>>>>>>> only see NOT_CHARGING if completely discharged *and* not discharging.
>>>>>>
>>>>>> I check the "Smart Battery Data Specification Revision 1.1".
>>>>>> And there are some words about FULLY_DISCHARGED.
>>>>>> "Discharge should be stopped soon."
>>>>>> "This status bit may be set prior to the
>>>>>> ‘TERMINATE_DISCHARGE_ALARM’ as an early or first level warning of end of
>>>>>> battery charge."
>>>>>> It looks like the FULLY_DISCHARGED status is used to announce the
>>>>>> warning of battery charge and it is still discharging if there is no one
>>>>>> takes care of it.
>>>>
>>>>
>>>> The only difference I see in the patch above is that in the case where
>>>> DISCHARGING isn't set, it won't check FULL_DISCHARGE. Nothing seems to
>>>> be changed in the case where FULL_DISCHARGE & DISCHARGING are set.
>>>
>>> If battery is dry(FULLY_DISCHARGED) and is charging(No
>>> BATTERY_DISCHARGING) by AC at the same time,
>>> I think it is better to mark as POWER_SUPPLY_STATUS_CHARGING.
>>> Is this right?
>>>
>>
>> Hmm. I can see where you patch would address that situation. From the
>> spec, it looks like its expected that the flags should look something
>> like this:
>>
>> capacity (in the course of running from fully_charged to dry to
>> recharging...)
>>
>> full: FULLY_CHARGED
>> <unplug>
>> high->low: DISCHARGING
>> ~0%: (DISCHARGING & FULLY_DISCHARGED)
>> <plug in>
>> ->~20%: FULLY_DISCHARGED
>>> ~20%: <nothing> = charging
>>
>> From this understanding, it seems like we can't expect FULLY_DISCHARGED
>> to ever be the only flag, nor can we expect it to go away when the
>> system is initially plugged in. In light of this, I can see why your
>> patch is preferable to the existing code, as the existing code could
>> imply that the system is either still near 0% when it is in fact
>> charging. Of course, ideally the status returned would be "LOW BUT
>> CHARGING" but I can see how CHARGING seems like a better option.
>>
>> I think this patch would be fine if we wanted to cover that case, though
>> if we do merge this, we should probably flush out the patch description
>> better to clarify why we have to treat FULLY_DISCHARGED as only
>> applicable while DISCHARGING. This, IMHO, isn't because the
>> FULLY_DISCHARGED flag comes on early, but rather because it doesn't turn
>> off until ~20%.
> 
> If I revise the description in this way(using your clear explanation):
> ------------------------------------------------------------------------
> The battery capacity changing course is like this:
> 
> full: BATTERY_FULLY_CHARGED => POWER_SUPPLY_STATUS_FULL
> <unplug AC>
> high->low: BATTERY_DISCHARGING => POWER_SUPPLY_STATUS_DISCHARGING
> ~0%: DISCHARGING & FULLY_DISCHARGED => POWER_SUPPLY_STATUS_NOT_CHARGING
> <plug in AC>
> 0%~20%: FULLY_DISCHARGED => POWER_SUPPLY_STATUS_CHARGING
> 20%~: No flag => POWER_SUPPLY_STATUS_CHARGING
> 
> For now, it is not exactly right to show the status as
> POWER_SUPPLY_STATUS_NOT_CHARGING when the battery is dry
> (FULLY_DISCHARGED) and AC is plugged in.
> Although the battery is in a low level, system works fine with the AC
> charging.
> It is better to say that the battery is charging.
> ------------------------------------------------------------------------

Sounds good.

> 
> How about this?
> By the way, should I also revise the title?
> 
well, since the case this is specifically addressing is more to do with
charging when very low than being dry, it would probably make sense to
change it to "sbs-battery: fix power status when battery charging near
dry" or something like that.

-rhyland


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