The gpio core looks at 'FLAG_BIAS_DISABLE' in preparation of calling the
gpiochip 'set_config()' hook. However, AFAICT, there's no way that this
flag is set because there's no support for it in firwmare code. Moreover,
in 'gpiod_configure_flags()', only pull-ups and pull-downs are being
handled.

On top of this, there are some users that are looking at
'PIN_CONFIG_BIAS_DISABLE' in the 'set_config()' hook. So, unless I'm
missing something, it looks like this was never working for these chips.

Note that the ACPI case is only compiled tested. At first glance, it seems
the current patch is enough but i'm not really sure...

As a side note, this came to my attention during this patchset [1]
(and, ofr OF,  was tested with it).

[1]: https://lore.kernel.org/linux-input/20220708093448.42617-5-nuno.sa@analog.com/ (local)

Nuno Sá (4):
  gpiolib: add support for bias pull disable
  gpiolib: of: support bias pull disable
  gpiolib: acpi: support bias pull disable
  dt-bindings: gpio: add pull-disable flag

 drivers/gpio/gpiolib-acpi.c     | 3 +++
 drivers/gpio/gpiolib-of.c       | 7 +++++++
 drivers/gpio/gpiolib.c          | 8 ++++++--
 include/dt-bindings/gpio/gpio.h | 3 +++
 include/linux/gpio/machine.h    | 1 +
 include/linux/of_gpio.h         | 1 +
 6 files changed, 21 insertions(+), 2 deletions(-)

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2.37.0