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Date:   Thu, 31 Aug 2017 01:58:09 -0700
From:   Liam Breck <liam@...workimprov.net>
To:     "H. Nikolaus Schaller" <hns@...delico.com>
Cc:     Sebastian Reichel <sre@...nel.org>,
        Pali Rohár <pali.rohar@...il.com>,
        "Andrew F. Davis" <afd@...com>,
        Linux PM mailing list <linux-pm@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>, kernel@...a-handheld.com
Subject: Re: [PATCH resend v2] power: supply: bq27xxx: enable writing capacity
 values for bq27421

On Wed, Aug 30, 2017 at 11:58 PM, H. Nikolaus Schaller
<hns@...delico.com> wrote:
> Hi Liam,
>
>> Am 30.08.2017 um 13:24 schrieb Liam Breck <liam@...workimprov.net>:
>>
>> Hi Nikolaus,
>>
>> On Wed, Aug 30, 2017 at 2:30 AM, H. Nikolaus Schaller <hns@...delico.com> wrote:
>>> Hi Liam and Sebastian,
>>>
>>>> Am 29.08.2017 um 22:20 schrieb Liam Breck <liam@...workimprov.net>:
>>>>
>>>> Hi Nikolaus, thanks for the patch...
>>>>
>>>> On Tue, Aug 29, 2017 at 1:10 PM, H. Nikolaus Schaller <hns@...delico.com> wrote:
>>>>> Tested on Pyra prototype with bq27421.
>>>>>
>>>>> Signed-off-by: H. Nikolaus Schaller <hns@...delico.com>
>>>>> ---
>>>>> drivers/power/supply/bq27xxx_battery.c | 2 +-
>>>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/power/supply/bq27xxx_battery.c b/drivers/power/supply/bq27xxx_battery.c
>>>>> index b6c3120ca5ad..e3c878ef7c7e 100644
>>>>> --- a/drivers/power/supply/bq27xxx_battery.c
>>>>> +++ b/drivers/power/supply/bq27xxx_battery.c
>>>>> @@ -688,7 +688,7 @@ static struct bq27xxx_dm_reg bq27545_dm_regs[] = {
>>>>> #define bq27545_dm_regs 0
>>>>> #endif
>>>>>
>>>>> -#if 0 /* not yet tested */
>>>>> +#if 1 /* tested on Pyra */
>>>>> static struct bq27xxx_dm_reg bq27421_dm_regs[] = {
>>>>
>>>> I think we can drop the #if and #else...#endif so it's just the
>>>> dm_regs table, as with bq27425.
>>>
>>> I have fixed that and did take the chance to update my OpenPandora
>>> kernel so that I also could test and make the bq27500 working.
>>
>> Is this gauge on the board or in the battery?
>
> It is on the board.
>
>> If in the battery,
>> monitored-battery should not be used.
>>
>> For a gauge on the board, if a user changes the battery to a different
>> type, they need to update the dtb.
>
> Well, that is a little difficult to control, but here we have only
> one standard Pandora cell. There may exist replacements with different
> capacity, but that should not be our problem...
>
>>
>> I assume you built with config_battery_bq27xxx_dt_updates_nvm?
>
> Yes.
>
>>
>>> The biggest hurdle was to find out that I have to change the
>>> compatible string to "ti,bq27500-1" to get non-NULL dm_regs...
>>>
>>> [   12.765930] bq27xxx_battery_i2c_probe name=bq27500-1-0
>>> [   12.771392] bq27xxx_battery_i2c_probe call setup
>>> [   12.874816] bq27xxx_battery_setup
>>> [   12.904266] bq27xxx_battery_setup: dm_regs=bf0520e0
>>> [   12.933380] (NULL device *): hwmon: 'bq27500-1-0' is not a valid name attribute, please fix
>>> [   13.234893] bq27xxx_battery_settings
>>> [   13.238891] bq27xxx-battery 2-0055: invalid battery:energy-full-design-microwatt-hours 14800000
>>
>> The chip does not support this param, so it should be zero, as it has
>> to be set if charge-full-design-* is set. Can you try that?
>
> Hm. IMHO the DT should describe what the battery has and the driver should simply ignore
> values it can't handle or reject them but do the best out of it. Telling the driver to ignore
> a value by setting to 0 would IMHO be the wrong approach.

The driver requires that if either charge- or energy-full-design is
set, then the other must be. Setting one and leaving the other at
default would be an error. Allowing any value for a field unsupported
by the chip, when supported field values must be within a range, isn't
useful for hw development or production scenarios. The solution for
shipped equipment is to drop the monitored-battery ref; see below.

> We are also working on the generic-adc-battery driver that makes use of the same battery DT
> node so that people can choose if they want to configure a kernel for fuel gauge or
> g-a-b or even both.
>
>>
>>> [   13.312469] bq27xxx_battery_set_config
>>> [   13.407745] bq27xxx_battery_unseal
>>> [   13.455993] bq27xxx_battery_update_dm_block
>>> [   13.460418] bq27xxx-battery 2-0055: update terminate-voltage to 3200
>>> [   13.694885] bq27xxx_battery_seal
>>
>> We need to see output after a reboot.
>
> This was the value after first boot with the new driver enabled.
>
> A second boot after removing and reinserting battery shows:
>
> [   11.256713] bq27xxx_battery_setup
> [   11.256744] bq27xxx_battery_setup: dm_regs=bf05b0e0
> [   11.257690] (NULL device *): hwmon: 'bq27500-1-0' is not a valid name attribute, please fix
> [   11.258056] bq27xxx_battery_settings
> [   11.258300] bq27xxx-battery 2-0055: invalid battery:energy-full-design-microwatt-hours 14800000
> [   11.258300] bq27xxx_battery_set_config
> [   11.258331] bq27xxx_battery_unseal

No mention of terminate-voltage in that run? Or is this truncated?
Looks like you didn't set energy-* to zero, so I can't tell if charge-* works.

>> Note that this chip has NVM so
>> these settings persist without power.
>
> Yes I know. Up to now the bq27500 has been programmed during production test
> by some special flashing tool. Now as the kernel driver has this capability,
> we should make (optionally) use of it.

The kernel driver has this feature primarily for gauges that lack NVM.
It sets those without config_battery_bq27xxx_dt_updates_nvm. The NVM
programming feature is for hw development and/or production. I don't
recommend it for shipped equipment.

>>
>>> Does this look ok for
>>>
>>>        bat: battery {
>>>                compatible = "simple-battery", "openpandora-battery";
>>>                voltage-min-design-microvolt = <3200000>;
>>>                energy-full-design-microwatt-hours = <14800000>;
>>>                charge-full-design-microamp-hours = <4000000>;
>>>        };
>>>
>>> ?
>
> I mainly had some initial doubts that it did not tell something like
> "update design-capacity" to 4000 or "design-capacity has 4000"
>
> Ah, I see:
>
>                 /* assume design energy & capacity are in same block */
>
> This means the bq27500 never programs capacity because we can't specify energy.
> So I't suggest to revise this rule and coupling of energy and capacity setting.

No, it failed to set charge-* because energy-* is out of range. Fix
that and it should just emit a warning about energy-* "buffer does not
match dm spec"

>>>
>>> I will send a patch for enabling both fuel gauges and the omap3-pandora-common.dtsi asap.
>>
>> You probably don't want this in upstream dts, as it only programs the
>> gauge if the kernel has the above config option. If the box runs a
>> stock distro, it won't work. A custom-built kernel with the above dts
>> programs the gauge unless the user sets the module param
>> dt_monitored_battery_updates_nvm=0. The requisite dtb should be
>> packaged with the custom-built kernel, and deployed with awareness of
>> the actual battery present.
>
> Imho, DT can and should describe all properties of the standard OpenPandora
> battery (and not missing registers of the bq27500).
>
> Using this information or not should be defined by different defconfigs.

Just omit monitored-battery from the bq27500 node on shipped devices.
We shall not program NVM on a stock kernel. And unfortunately you
can't send an NVM gauge temporary params.

NB: the DT battery node is new and all the implications have not been
discovered.

This BQ27 feature was begun in December of last year, and I'm a little
tired of thinking about it. Feel free to suggest improvements, but be
aware that we might have already considered and rejected them :-)

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