My first question on StackExchange.
I have set up a Raspberry Pi 2 with the latest Raspbian (Buster Lite 2019-09-26 Kernel version: 4.19). I want to use a module that was not compiled into this image. Is it possible to compile only that module, using the tools and files available on the Pi itself?
The module I want is this one: https://github.com/raspberrypi/linux/blob/rpi-4.19.y/drivers/auxdisplay/ht16k33.c
It was not included when the image was compiled. The only drivers I have in this section are these:
ls /lib/modules/4.19.75-v7+/kernel/drivers/auxdisplay/ charlcd.ko hd44780.ko
I have searched for answers, and the only thing that came close was this: How compile a loadable kernel module without recompiling kernel
However it talks about making your own modules, not compiling an existing one. Other discussions talk about building the entire kernel.
Once I have the module I will load it using Device Tree (which I know how to do).
Thanks to @ingo for the hint, but I haven't got it working yet. I found this article:
I can successfully compile the module, but I get errors due to unknown symbols. My source file was the ht16k33.c code linked from GitHub above and placed in a subdirectory of user pi. The Makefile is as follows, copied from the article:
obj-m := ht16k33.o KDIR := /lib/modules/$(shell uname -r)/build PWD := $(shell pwd) default: $(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules
Running make is successful:
make -C /lib/modules/4.19.75-v7+/build SUBDIRS=/home/pi/projects/ht16k33 modules make: Entering directory '/usr/src/linux-headers-4.19.75-v7+' CC [M] /home/pi/projects/ht16k33/ht16k33.o Building modules, stage 2. MODPOST 1 modules CC /home/pi/projects/ht16k33/ht16k33.mod.o LD [M] /home/pi/projects/ht16k33/ht16k33.ko make: Leaving directory '/usr/src/linux-headers-4.19.75-v7+'
When I try and load the module I get this error:
sudo insmod ht16k33.ko insmod: ERROR: could not insert module ht16k33.ko: Unknown symbol in module
And the following reported in /var/log/messages:
Jan 7 17:20:23 soap kernel: [99203.981258] ht16k33: loading out-of-tree module taints kernel. Jan 7 17:20:23 soap kernel: [99203.981943] ht16k33: Unknown symbol matrix_keypad_build_keymap (err -2) Jan 7 17:20:23 soap kernel: [99203.982082] ht16k33: Unknown symbol fb_sys_write (err -2) Jan 7 17:20:23 soap kernel: [99203.982142] ht16k33: Unknown symbol sys_imageblit (err -2) Jan 7 17:20:23 soap kernel: [99203.982214] ht16k33: Unknown symbol sys_fillrect (err -2) Jan 7 17:20:23 soap kernel: [99203.982300] ht16k33: Unknown symbol matrix_keypad_parse_properties (err -2) Jan 7 17:20:23 soap kernel: [99203.982380] ht16k33: Unknown symbol sys_copyarea (err -2) Jan 7 17:20:23 soap kernel: [99203.982460] ht16k33: Unknown symbol fb_sys_read (err -2)
Edit: Further reading and experimentation led me to this course of action:
- Copy the ht16k33.ko file produced to /lib/modules/4.19.75-v7+/extra
- sudo depmod
- modprobe ht16k33
tail /var/log/messages Jan 7 19:30:51 soap kernel: [107031.622336] input: ht16k33-keypad as /devices/platform/soc/3f804000.i2c/i2c-1/1-0070/input/input0
I think I'm done. Thanks.
If I've done it wrong then I'd be happy to tidy up this explanation.