[BananaPro][Mainline] Loud hum when there is no audio output

[pm39]

Greetings, all!

 

I've got a LeMaker A20 BananaPro, on which I'm using the Armbian mainline distribution (for a more complete description of my setup, please see below). I'm using a serial console to the board; I'm not connecting anything to HDMI for display. I'm running the distribution off of a brand new 8Gig SanDisk Extreme Pro. I would like to use alsa (at least in part) in the audio stack. I'm experiencing the following:

 

1. When I have no audio playing through the audio out jack, I get a loud (powerline, probably) hum on my speakers.
2. When I start audio playback (a wav through aplay, or an mp3 through mpd, etc.) the hum disappears, and the sound quality is fine.
3. If I pause or stop playback, the hum resumes roughly seven seconds after the audio stops. The pause between the audio stopping and the hum seems consistant.

 

I have found in my research a similar problem people have been having with Ubuntu: http://www.linuxquestions.org/questions/linux-general-1/buzzing-sound-from-speakers-only-when-no-sound-is-playing-ubuntu-kk-790610/ ...which seems to be due to a power saving feature of the driver, but I can't find any reference to a similar feature for the sun4i_codec module.

 

Can anyone offer assistance? I'm not sure what to try next. I'm very happy to test things, try things, etc. Thanks!

 

    -Paul

 

Various configuration details below.

 

Results of uname -a:

Linux hostname 4.9.12-sunxi #4 SMP Thu Feb 23 19:46:51 CET 2017 armv7l GNU/Linux

Contents of /etc/armbian-release:

# PLEASE DO NOT EDIT THIS FILE
BOARD=bananapipro
BOARD_NAME="Banana Pi Pro"
VERSION=5.25
LINUXFAMILY=sunxi
BRANCH=next
ARCH=arm
IMAGE_TYPE=stable

Results of lsmod:

Module                  Size  Used by
sun4i_codec            10104  3 
snd_soc_core           97876  1 sun4i_codec
ir_lirc_codec           4088  0 
snd_pcm_dmaengine       2770  1 snd_soc_core
evdev                   9412  1 
lirc_dev                6245  1 ir_lirc_codec
snd_pcm                57757  3 snd_pcm_dmaengine,snd_soc_core
snd_timer              14809  1 snd_pcm
snd                    35783  4 snd_timer,snd_soc_core,snd_pcm
sun4i_ts                3414  0 
soundcore                858  1 snd
sunxi_cir               3159  0 
nvmem_sunxi_sid         1967  0 
nvmem_core              7158  1 nvmem_sunxi_sid
sun4i_ss               13213  0 
cpufreq_dt              2920  0 
uio_pdrv_genirq         2780  0 
uio                     6272  1 uio_pdrv_genirq
bonding                82855  0 
brcmfmac              144129  0 
brcmutil                4189  1 brcmfmac
cfg80211              337391  1 brcmfmac
rfkill                  8383  2 cfg80211
fuse                   62841  1 
realtek                 2583  0 

 

[pm39]

Well nuts; I didn't search enough.

 

The workaround detailed here:

...looks like it's working for me.