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Subject: Re: [PATCHv1 00/19] Improve SBS battery support
To:     Sebastian Reichel <sebastian.reichel@collabora.com>
Cc:     Rob Herring <robh+dt@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J . Wysocki" <rafael@kernel.org>, linux-pm@vger.kernel.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel@collabora.com,
        'Linux Samsung SOC' <linux-samsung-soc@vger.kernel.org>
From:   Marek Szyprowski <m.szyprowski@samsung.com>
Message-ID: <a210e6e0-32db-98e9-f217-cec538407191@samsung.com>
Date:   Wed, 3 Jun 2020 20:49:37 +0200
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References: <20200513185615.508236-1-sebastian.reichel@collabora.com>
        <CGME20200601104027eucas1p2b076ee860520d709e8178c41550653f7@eucas1p2.samsung.com>
        <15933a91-dd89-1f94-c2f2-79be4395f4c1@samsung.com>
        <20200601170528.r5w3aeijny3v5yx3@earth.universe>
        <b3fd35de-1dd6-1ddc-7e57-2d9ab2860e81@samsung.com>
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Hi Sebastian,

On 02.06.2020 20:01, Sebastian Reichel wrote:
> On Tue, Jun 02, 2020 at 09:17:09AM +0200, Marek Szyprowski wrote:
>> On 01.06.2020 19:05, Sebastian Reichel wrote:
>>> On Mon, Jun 01, 2020 at 12:40:27PM +0200, Marek Szyprowski wrote:
>>>> On 13.05.2020 20:55, Sebastian Reichel wrote:
>>>>> This patchset improves support for SBS compliant batteries. Due to
>>>>> the changes, the battery now exposes 32 power supply properties and
>>>>> (un)plugging it generates a backtrace containing the following message
>>>>> without the first patch in this series:
>>>>>
>>>>> ---------------------------
>>>>> WARNING: CPU: 0 PID: 20 at lib/kobject_uevent.c:659 add_uevent_var+0xd4/0x104
>>>>> add_uevent_var: too many keys
>>>>> ---------------------------
>>>>>
>>>>> For references this is what an SBS battery status looks like after
>>>>> the patch series has been applied:
>>>>>
>>>>> cat /sys/class/power_supply/sbs-0-000b/uevent
>>>>> POWER_SUPPLY_NAME=sbs-0-000b
>>>>> POWER_SUPPLY_TYPE=Battery
>>>>> POWER_SUPPLY_STATUS=Discharging
>>>>> POWER_SUPPLY_CAPACITY_LEVEL=Normal
>>>>> POWER_SUPPLY_HEALTH=Good
>>>>> POWER_SUPPLY_PRESENT=1
>>>>> POWER_SUPPLY_TECHNOLOGY=Li-ion
>>>>> POWER_SUPPLY_CYCLE_COUNT=12
>>>>> POWER_SUPPLY_VOLTAGE_NOW=11441000
>>>>> POWER_SUPPLY_CURRENT_NOW=-26000
>>>>> POWER_SUPPLY_CURRENT_AVG=-24000
>>>>> POWER_SUPPLY_CAPACITY=76
>>>>> POWER_SUPPLY_CAPACITY_ERROR_MARGIN=1
>>>>> POWER_SUPPLY_TEMP=198
>>>>> POWER_SUPPLY_TIME_TO_EMPTY_AVG=438600
>>>>> POWER_SUPPLY_TIME_TO_FULL_AVG=3932100
>>>>> POWER_SUPPLY_SERIAL_NUMBER=0000
>>>>> POWER_SUPPLY_VOLTAGE_MIN_DESIGN=10800000
>>>>> POWER_SUPPLY_VOLTAGE_MAX_DESIGN=10800000
>>>>> POWER_SUPPLY_ENERGY_NOW=31090000
>>>>> POWER_SUPPLY_ENERGY_FULL=42450000
>>>>> POWER_SUPPLY_ENERGY_FULL_DESIGN=41040000
>>>>> POWER_SUPPLY_CHARGE_NOW=2924000
>>>>> POWER_SUPPLY_CHARGE_FULL=3898000
>>>>> POWER_SUPPLY_CHARGE_FULL_DESIGN=3800000
>>>>> POWER_SUPPLY_CONSTANT_CHARGE_CURRENT_MAX=3000000
>>>>> POWER_SUPPLY_CONSTANT_CHARGE_VOLTAGE_MAX=12300000
>>>>> POWER_SUPPLY_MANUFACTURE_YEAR=2017
>>>>> POWER_SUPPLY_MANUFACTURE_MONTH=7
>>>>> POWER_SUPPLY_MANUFACTURE_DAY=3
>>>>> POWER_SUPPLY_MANUFACTURER=UR18650A
>>>>> POWER_SUPPLY_MODEL_NAME=GEHC
>>>> This patch landed in linux-next dated 20200529. Sadly it causes a
>>>> regression on Samsung Exynos-based Chromebooks (Exynos5250 Snow,
>>>> Exynos5420 Peach-Pi and Exynos5800 Peach-Pit). System boots to
>>>> userspace, but then, when udev populates /dev, booting hangs:
>>>>
>>>> [    4.435167] VFS: Mounted root (ext4 filesystem) readonly on device
>>>> 179:51.
>>>> [    4.457477] devtmpfs: mounted
>>>> [    4.460235] Freeing unused kernel memory: 1024K
>>>> [    4.464022] Run /sbin/init as init process
>>>> INIT: version 2.88 booting
>>>> [info] Using makefile-style concurrent boot in runlevel S.
>>>> [    5.102096] random: crng init done
>>>> [....] Starting the hotplug events dispatcher: systemd-udevdstarting
>>>> version 236
>>>> [ ok .
>>>> [....] Synthesizing the initial hotplug events...[ ok done.
>>>> [....] Waiting for /dev to be fully populated...[   34.409914]
>>>> TPS65090_RAILSDCDC1: disabling
>>>> [   34.412977] TPS65090_RAILSDCDC2: disabling
>>>> [   34.417021] TPS65090_RAILSDCDC3: disabling
>>>> [   34.423848] TPS65090_RAILSLDO1: disabling
>>>> [   34.429068] TPS65090_RAILSLDO2: disabling
>>> :(
>>>
>>> log does not look useful either.
>>>
>>>> Bisect between v5.7-rc1 and next-20200529 pointed me to the first bad
>>>> commit: [c4b12a2f3f3de670f6be5e96092a2cab0b877f1a] power: supply:
>>>> sbs-battery: simplify read_read_string_data.
>>> ok. I tested this on an to-be-upstreamed i.MX6 based system
>>> and arch/arm/boot/dts/imx53-ppd.dts. I think the difference
>>> is, that i2c-exynos5 does not expose I2C_FUNC_SMBUS_READ_BLOCK_DATA.
>>> I hoped all systems using SBS battery support this, but now
>>> I see I2C_FUNC_SMBUS_EMUL only supports writing block data.
>>> Looks like I need to add another patch implementing that
>>> using the old code with added PEC support.
>>>
>>> In any case that should only return -ENODEV for the property
>>> (and uevent), but not break boot. So something fishy is going
>>> on.
>>>
>>>> However reverting it in linux-next doesn't fix the issue, so the
>>>> next commits are also relevant to this issue.
>>> The next patch, which adds PEC support depends on the simplification
>>> of sbs_read_string_data. The old, open coded variant will result in
>>> PEC failure for string properties (which should not stop boot either
>>> of course). Can you try reverting both?
>> Indeed, reverting both (and fixing the conflict) restores proper boot.
> Ok, I pushed out a revert of those two patches. They should land in
> tomorrows linux-next release. Please test it.


Today's linux-next (20200603) boots fine on the Samsung Exynos-based 
Chromebooks. Let me know how if you need any help debugging the issues 
to resurrect those patches.


>>> If that helps I will revert those two instead of dropping the whole
>>> series for this merge window.
>>>
>>>> Let me know how can I help debugging it.
>>> I suspect, that this is userspace endlessly retrying reading the
>>> battery uevent when an error is returned. Could you check this?
>>> Should be easy to see by adding some printfs.
>> I've added some debug messages in sbs_get_property() and it read the
>> same properties many times. However I've noticed that if I wait long
>> enough booting finally continues.
> So basically userspace slows down itself massively by trying to
> re-read uevent over and over when an error occurs. Does not seem
> like a sensible thing to do. I will have a look at this when I find
> some time.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland