Date:   Thu, 31 Aug 2017 11:35:33 +0200
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Liam Breck <liam@...workimprov.net>,
        Sebastian Reichel <sre@...nel.org>
Cc:     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

Hi Liam,

> Am 31.08.2017 um 10:58 schrieb Liam Breck <liam@...workimprov.net>:
> 
> 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?

No, I didn't see it again.

> Or is this truncated?
> Looks like you didn't set energy-* to zero, so I can't tell if charge-* works.

Seems to need more experimentation (and more time for it).

> 
>>> 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.

Mostly agreed...

> 
>>> 
>>>> 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"

Here I strongly disagree. The DT property should describe the battery and not
a limitation of the fuel gauge chip or the value is not in the range of what
the chip expects.

IMHO, if the fuel gauge driver can't handle, it should not require to tamper
with the battery DT description making it wrong and unuseable for other purposes.

> 
>>>> 
>>>> 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.

Isn't this what the defconfigs are for?

A stock kernel should keep CONFIG_BATTERY_BQ27XXX_DT_UPDATES_NVM disabled
and I haven't seen that it is enabled in a stock defconfig.

A production kernel (or user wanting to play with it) can enable. But
should not change the DTB.

I have done the same mistake to mis-use DT as "configuration" or ask users to
install different DTB several times myself and was heavily criticized,
because maintainers clearly said DT should *describe* hardware and not configure
kernel features. I.e. there should be only one DTB for each board.

Hence I would expect them to say: if the bq27500 monitors the battery
it should be described by the DT. And if the battery has some
energy-full-design-microwatt-hours, it should be there and not a "0" or
omission.

But that is just *my* 2ct. DT maintainers should finally say something.

> 
> 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.

I fully understand :) I have some patches in tiresome discussion since ca. 3 years...

>  Feel free to suggest improvements, but be
> aware that we might have already considered and rejected them :-)


We had observed this issue for the RAM only fuel gauge bq27421 a while ago
(I think even before December) and had started our own patch set. Grazvydas
recently had made it working on some older kernel which is now superseded by
your patch set. So you were faster in submitting a solution (and yours is
even more general than what we had ever thought about).

So I am very pleased with that we have a big step forward for the bq27421
based device. Making the bq27500 in the OpenPandora fool proof isn't that important
for the moment so we can postpone it.

BR and thanks for all the work,
Nikolaus

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