Unknown symbol fb_deferred_io_init + fb_deferred_io_cleanup

[tfindlay-au]

Hi Folks, I have a NanoPi M4 (rk3399) with 4.4.167-rk3399 kernel. I have been trying to build a new kernel with fbtft support, it makes the modules, installs them but when I load it via: sudo modprobe fbtft_device rotate=90 name=piscreen speed=16000000 gpios=reset:2,dc:71 txbuflen=32768 fps=25 dmesg:

[   61.631097] fbtft: module is from the staging directory, the quality is unknown, you have been warned.
[   61.631373] fbtft: Unknown symbol fb_deferred_io_init (err 0)
[   61.631391] fbtft: Unknown symbol fb_deferred_io_cleanup (err 0)

The screen is a FriendlyElec 2.8" with the ST7789V in it. Any tips on what I'm doing wrong ? It's been 20 years since I built a kernel from the console before, so I'm a bit rusty.

[tfindlay-au]

Just for reference, modinfo show the modules as follows:

root@nanopim4:~# modinfo fbtft
filename:       /lib/modules/4.4.167-rk3399/kernel/drivers/staging/fbtft/fbtft.ko
license:        GPL
depends:
staging:        Y
intree:         Y
vermagic:       4.4.167-rk3399 SMP mod_unload aarch64
parm:           debug:override device debug level (ulong)
parm:           dma:Use DMA buffer (bool)
root@nanopim4:~# modinfo fb_st7789v
filename:       /lib/modules/4.4.167-rk3399/kernel/drivers/staging/fbtft/fb_st7789v.ko
license:        GPL
author:         Dennis Menschel
description:    FB driver for the ST7789V LCD Controller
alias:          platform:st7789v
alias:          spi:st7789v
alias:          platform:fb_st7789v
alias:          spi:fb_st7789v
alias:          of:N*T*Csitronix,st7789v*
depends:        fbtft
staging:        Y
intree:         Y
vermagic:       4.4.167-rk3399 SMP mod_unload aarch64
root@nanopim4:~#

[notro]

fbtft: Unknown symbol fb_deferred_io_init (err 0)

This indicates that CONFIG_FB_DEFERRED_IO is not enabled. It is set by the fbtft Kconfig though: https://elixir.bootlin.com/linux/v4.4.167/source/drivers/staging/fbtft/Kconfig