gpio-omap: add support gpiolib bias (pull-up/down) flags?

[Drew Fustini <drew@xxxxxxxx>]

Hello Grygorii, Santosh and Kevin,

You are listed as gpio-omap maintainers so I wanted to reach out and
get your feedback on this.

The gpiolib userspace API added support for bias flags
(pull-up/pull-down) in Linux 5.5:
[GIT PULL] GPIO changes for v5.5 [1]

The merged code is from the patch series:
[PATCH v6 0/7] gpio: expose line bias flags to userspace [2]

The gpiochip character device now supports theses flags [3]:
GPIOHANDLE_REQUEST_BIAS_PULL_UP
GPIOHANDLE_REQUEST_BIAS_PULL_DOWN
GPIOHANDLE_REQUEST_BIAS_DISABLE

The pinctrl-bcm2835 driver used on Raspberry Pi already supports the
pull-up/down bias flags [4].  pinctrl-bcm2835 is also a gpio driver
[5].  libgpiod v1.5 supports these bias flags [6], so the command line
gpioset utility can set the bias flags for a line on the Raspberry Pi
[7].

I would like the BeagleBone, which has the TI AM3358 SoC, to be able
to use the bias flags as well.   The AM3358 uses the gpio-omap GPIO
driver.  However, gpio-omap does not support these flags [8].

Do you have any feedback on whether this is possible to implement?

If so, do you have any guidance about the correct way for me to add
support for those bias flags in gpio-omap.c?

Thank you,
Drew

[1] https://www.spinics.net/lists/linux-gpio/msg43719.html
[2] https://lore.kernel.org/linux-gpio/CACRpkdbJxcfj6pK=1qjXxffFn0RUH9VD0HRFXX0RoZJDi=hfRw@xxxxxxxxxxxxxx/
[3] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/gpio/gpiolib.c#n1061
[4] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/pinctrl/bcm/pinctrl-bcm2835.c#n958
[5] https://www.kernel.org/doc/Documentation/devicetree/bindings/pinctrl/brcm,bcm2835-gpio.txt
[6] https://git.kernel.org/pub/scm/libs/libgpiod/libgpiod.git/commit/?h=v1.5.x&id=26d8d8f0b7bc0e300aaab05c75d5af1b0686af08
[7] https://microhobby.com.br/blog/2020/02/02/new-linux-kernel-5-5-new-interfaces-in-gpiolib/
[8] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/gpio/gpio-omap.c