aplay -l doesn't see my loopback sound card using snd_aloop

[Jeff Tchang <jeff.tchang@xxxxxxxxx>]

I have an embedded system with a custom kernel. I have built snd_aloop as a kernel module and am able to load it. However aplay -l or aplay -L does not show any devices. However the loopback device is showing up in /proc/asound/cards so I am wondering what could be the problem.

Details:

# uname -a
Linux openmiko 3.10.14 #7 PREEMPT Sat Sep 5 21:33:15 UTC 2020 mips GNU/Linux

# aplay --version

aplay: version 1.1.0 by Jaroslav Kysela <perex@xxxxxxxx>

I see the loopback card:

# cat /proc/asound/cards
 3 [Loopback       ]: Loopback - Loopback
                      Loopback 1

But aplay -l gives me nothing:

# aplay -l


********************   WARNING   *******************************
Warning! aplay uses ALSA emulation instead of the native OSS API
****************************************************************

aplay: device_list:268: no soundcards found...
#

# lsmod
Module                  Size  Used by    Tainted: G  
snd_aloop              12002  0
snd_pcm                68453  1 snd_aloop
snd_page_alloc          3810  1 snd_pcm
snd_timer              18670  1 snd_pcm
snd                    39168  3 snd_aloop,snd_pcm,snd_timer
v4l2loopback           22369  2
sensor_jxf23            9136  1
tx_isp                337860  3
sinfo                  12972  0
#

More details:

# cat /proc/asound/
Loopback/  cards      modules    timers
card3/     devices    pcm        version
# cat /proc/asound/pcm
03-00: Loopback PCM : Loopback PCM : playback 2 : capture 2
03-01: Loopback PCM : Loopback PCM : playback 2 : capture 2
# cat /proc/asound/modules
 3 snd_aloop
# cat /proc/asound/devices
 33:        : timer
 96: [ 3]   : control
112: [ 3- 0]: digital audio playback
113: [ 3- 1]: digital audio playback
120: [ 3- 0]: digital audio capture
121: [ 3- 1]: digital audio capture

My goal is to read from /dev/dsp (OSS legacy) and output it to the loopback device so a program that only uses ALSA can have audio. I plan to use ffmpeg. Ffmpeg does not see the hardware either.

I have tried variations of:

ffmpeg -f oss -i /dev/dsp -codec:a pcm_s16le -f alsa hw:3,0

ffmpeg -f oss -i /dev/dsp -codec:a pcm_s16le -f alsa hw:3,1

I tried poking around in the kernel sources but no real smoking gun. The vendor has their own sound device drivers. Is it possible it is somehow interfering with getting a full device list?

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