Hi,

On Tue, Jun 02, 2020 at 09:17:09AM +0200, Marek Szyprowski wrote:
> Hi Sebastian,
> 
> 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.

> > 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.

-- Sebastian