[alsa-devel] Building a new out-of-tree ALSA module on Ubuntu Xenial (was gitcompile fail)

[Mark Brand]

Hi all

My abundant thanks to Clemens and Takashi for your kind and patient 
assistance.  May I now answer my own question by offering the following 
step-by-step procedure in case anyone comes looking for it?  Any 
improvements or suggestions would be greatly appreciated too, thank you.

$ sudo apt-get install linux-headers-$(uname -r)
$ sudo mkdir /lib/modules/$(uname -r)/updates
$ sudo apt-get build-dep linux-image-$(uname -r)
$ mkdir $HOME/src; cd $HOME/src
$ apt-get source linux-image-$(uname -r)
$ cd linux-$(uname -r | awk -F - '{print $1}')

Now I am at the root of the kernel source tree.  In my case, I want to 
add a new driver for an as-yet unsupported device.  I find a supported 
device that appears substantially similar to what I need 
(sound/drivers/mtpav.c) and base my hack on that - producing 
sound/drivers/mq8portse.c.  I then add the following lines to the 
sound/drivers/Makefile (each mirroring entries found in respect of mtpav.c)

snd-mq8portse-objs := mq8portse.o

obj-$(CONFIG_SND_MQ8PORTSE) += snd-mq8portse.o

Now (from the root of the kernel source tree):

$ cd sound/drivers/
$ CONFIG_SND_MQ8PORTSE=m make -C /lib/modules/$(uname -r)/build M=$(pwd) 
snd-mq8portse.ko

This produces my module in the same folder, which I copy to the updates 
folder.

$ sudo cp snd-mq8portse.ko /lib/modules/$(uname -r)/updates/
$ sudo depmod -a

Now, because my particular device is attached to the LPT port, I need to 
unload the lp driver before snd-mq8portse will load.
$ sudo modprobe -r lp
$ sudo modprobe snd-mq8portse
$ modinfo snd-mq8portse

I try it out in my ALSA client ... then remove ...

$ sudo modprobe -r snd-mq8portse

The MusicQuest 8Port/SE is attached to the LPT port, so a more permanent 
setup requires that I blacklist all typical parport stuff.  I add the 
following as /etc/modprobe.d/blacklist-parport.conf:

# keep LPT port open for mq8portse
alias parport_pc off
alias parport off

blacklist parport_pc
blacklist parport
blacklist ppdev
blacklist lp

I also comment out autoloading of lp in /etc/modules.  I can then add 
mq8portse to /etc/modules for automatic loading, unless I want to defer 
to manual modprobe-ing.

Once again, thank you ever so much, one and all.  Next I need to find 
out how to submit this driver for inclusion in ALSA.

*Mark Brand*
Lecturer in Music Technology
School of Music, Art & Design
Summerstrand Campus (South)
Tel: +27 (0)41 5042250
Fax: +27 (0)41 5042507