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

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Message-ID: <56F95451.5040607@nvidia.com>
Date:	Mon, 28 Mar 2016 11:57:05 -0400
From:	Rhyland Klein <rklein@...dia.com>
To:	Daniel Kurtz <djkurtz@...omium.org>,
	YH Huang <yh.huang@...iatek.com>
CC:	Sebastian Reichel <sre@...nel.org>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Matthias Brugger <matthias.bgg@...il.com>,
	<linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"moderated list:ARM/Mediatek SoC support" 
	<linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH] sbs-battery: fix power status when battery is dry

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.

I think in the case that both flags are set, it makes sense to
prioritize the FULL_DISCHARGE, since as quote above actually starts with
"FULLY_DISCHARGED bit is set when the Smart Battery determines that it
has supplied all the charge it can." I think at the point where both
statuses are reported, the fact that it is still DISCHARGING doesn't
matter. The code as is handles this in that manner, so I don't see a
need to change it.

-rhyland


-- 
nvpublic