Generic CONFIG_SERIAL_DEV_CTRL_TTYPORT to be disabled to enable BBB overlay /dev/ttySC0

Generic CONFIG_SERIAL_DEV_CTRL_TTYPORT to be disabled to enable BBB overlay /dev/ttySC0

[Zoran Stojsavljevic]

Hello list,

I have an interesting problem, which is described here:
https://www.spinics.net/lists/linux-serial/msg22566.html

I experienced the same problem on BeagleBone Black platform (armv7 A8:
am335x silicon), and the overlay is shown here:
https://github.com/ZoranStojsavljevic/MikroE_BeagleBone-Black_BSP-Integration/blob/master/BBB-debian_buster/Master_Example_i2c2_sc16is740.md

And the overlay written for /dev/ttySC0 is given here:
https://github.com/ZoranStojsavljevic/MikroE_BeagleBone-Black_BSP-Integration/blob/master/BBB-debian_buster/overlay_examples/i2c2_sc16is740/BB-I2C2-SC16IS740-00A0.dts

In order to solve this problem, I disabled the following option in
kernel .config:
## CONFIG_SERIAL_DEV_CTRL_TTYPORT is not set

But I am unsure why keeping enabled generic serial tty bus, and
disabling the generic serial tty device driver enables /dev/ttySC0 on
the target BBB platform.
https://github.com/ZoranStojsavljevic/MikroE_BeagleBone-Black_BSP-Integration/blob/master/BBB-debian_buster/overlay_examples/KERNEL.md

Just disabling CONFIG_SERIAL_DEV_CTRL_TTYPORT gives a working /dev/ttySC0 :

      │ Symbol: SERIAL_DEV_CTRL_TTYPORT [=n]
      │ Type  : bool
      │ Prompt: Serial device TTY port controller
      │   Location:
      │     -> Device Drivers
      │       -> Character devices
      │ (1)     -> Serial device bus (SERIAL_DEV_BUS [=y])
      │   Defined at drivers/tty/serdev/Kconfig:14
      │   Depends on: TTY [=y] && SERIAL_DEV_BUS [=y]=y

Again, appears that the generic serial tty bus is enabled, but the
solution of the problem is to disable generic tty driver (not sure
why)!

I hope somebody already encounter this problem from this list.

Thank you in advance,
Zoran Stojsavljevic