/dev/spidev2.1 cannot be used in UP Board

[pazeshun]

I want to use /dev/spidev2.1 in UP Board, which is written here.
However, this cannot be used because the chip-select pin doesn't work.
How can I make /dev/spidev2.1 work?

[pazeshun]

Details

I installed Ubuntu 16.04 and kernel 4.15.0 for UP by following https://wiki.up-community.org/Ubuntu#Install_Ubuntu_kernel_4.15.0_for_UP_from_PPA_on_Ubuntu_16.04:

$ cat /etc/lsb-release 
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=16.04
DISTRIB_CODENAME=xenial
DISTRIB_DESCRIPTION="Ubuntu 16.04.6 LTS"
$ uname -a
Linux *** 4.15.0-37-generic #40~upboard03-Ubuntu SMP Wed Dec 12 16:21:24 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

However,

$ ls -l /dev/spidev2.1
ls: cannot access '/dev/spidev2.1': No such file or directory

I found that /dev/spidev2.1 is disabled unless the module parameter up_board.spidev1 is set at https://github.com/emutex/ubilinux-kernel/blob/upboard-4.9/drivers/platform/x86/up_board.c#L45-L47.
So I added up_board.spidev1=Y to the kernel command line (GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub) and got /dev/spidev2.1.
But communication via /dev/spidev2.1 failed due to the chip-selection pin (GPIO22) didn't become 0V.

I found old code modifies SPI module to work /dev/spidev2.1, but this code is lost in the latest kernel:
cb1756d
Instead, I found the following commit to support GPIO chip select (required for /dev/spidev2.1), but I couldn't understand how to use this feature:
99f499c