[PATCH V2 0/4] Fix Incorrect State of Charge for RK817

[Chris Morgan]

From: Chris Morgan <macromorgan at hotmail.com>

Users of the popular firmware RockNIX had identified a few bugs with
accurately displaying the correct state of charge for RK817 battery
devices. With the help of one user analyzing the code with Claude
they were able to identify a few potential bugs along with potential
solutions which I was then able to verify. These bugs are as follows:

1) Incorrectly clamping a value with a max of 10000 instead of 100000.
This bug caused the state of charge to sometimes read as 10% instead
of 100% as it should have.

2) Using the boot_voltage value to calibrate the battery in scenarios
where it could not be trusted. The boot_voltage register populates
immediately at power-on, and the driver would check if this value
was older than 30 minutes before using it. Unfortunately when combined
with the default behavior of the bootloader to turn the device off
when plugged in (requiring a user to explicitly power the device on)
the boot_voltage and boot_timer values were wrong. The boot voltage
would not account for any voltage added while the device was off,
and the boot_counter that tracks the time the device was off would
be reset. To fix this we changed the behavior to (outside of first-boot
scenarios) use a value saved to NVRAM, the value from the coulomb
counter directly, and an OCV lookup from the live battery voltage,
and then using those values provide an initial "guess" of the state
of charge and recalibrate with the OCV voltage once it is available.

Included in this series is another fix that would cause the battery
to drain while the system was shut down. This patch replicates the
Rockchip BSP driver to clear a shutdown register. Unlike the BSP there
is no behavior to bypass this since no boards have yet been observed
using the SYS_CAN_SD bypass on the BSP kernel.

Changes Since V1:
 - Dropped the sleep fixes, as I would like to test them a bit more
   extensively first.
 - Dropped the devicetree parameter, as since no boards have *yet*
   needed to alter the default behavior there's no need for it.
 - Changed the behavior of how we select the initial SOC and made
   it its own function to ease in code readibility. This new method
   was tested with various boot scenarios. The average error was less
   than 5%, and in a worst case scenario where the device was
   discharged to 0%, then left to charge at the bootloader the device
   over-reported its state of charge by about 10%. When this occurred
   the device reported its SOC as 100% but that it was charging, which
   was corrected by the new OCV logic that kicked in once charging
   completed.
 - Scrapped the more complicated sleep fix in favor of simply telling
   the battery to recalibrate at full after suspend, in case of a 
   counting anomaly. 

Chris Morgan (4):
  power: supply: rk817-charger: Fix NVRAM SoC Value
  power: supply: rk817-charger: Resolve boot state of charge from the
    coulomb counter
  power: supply: rk817-charger: Clear SYS_CAN_SD register by default
  power: supply: rk817-charger: Clear full charge cal on resume

 drivers/power/supply/rk817_charger.c | 313 ++++++++++++++++++++-------
 include/linux/mfd/rk808.h            |   3 +
 2 files changed, 239 insertions(+), 77 deletions(-)

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2.53.0