Hello alsa-dev / linux-amlogic,
I’d like to describe a problem with speaker placement seen with the Amlogic (meson) AIU and AXG audio drivers. Playing media in Kodi I’d noticed that placement is consistently wrong; meaning the incorrect placement remains the same over different media and Amlogic hardwares.
This was traced to a failure to get the channel map via snd_pcm_get_chmap() and further analysis showed this failed because the PCM controls are exposed on a different device than the PCM stream.
e.g. on LibreTech LePotato with DPCM routing configured for HDMI output, the hw PCM is on the single frontend device 0 but the PCM controls are on device 2:
LePotato:~ # aplay -l **** List of PLAYBACK Hardware Devices **** card 0: LIBRETECHCC [LIBRETECH-CC], device 0: fe.dai-link-0 (*) [] Subdevices: 1/1 Subdevice #0: subdevice #0
LePotato:~ # amixer controls numid=19,iface=MIXER,name='PCM Playback Volume' numid=18,iface=MIXER,name='ACODEC Left DAC Sel' numid=7,iface=MIXER,name='ACODEC Mute Ramp Switch' numid=2,iface=MIXER,name='ACODEC Playback Channel Mode' numid=3,iface=MIXER,name='ACODEC Playback Switch' numid=4,iface=MIXER,name='ACODEC Playback Volume' numid=5,iface=MIXER,name='ACODEC Ramp Rate' numid=17,iface=MIXER,name='ACODEC Right DAC Sel' numid=8,iface=MIXER,name='ACODEC Unmute Ramp Switch' numid=6,iface=MIXER,name='ACODEC Volume Ramp Switch' numid=1,iface=MIXER,name='AIU ACODEC I2S Lane Select' numid=16,iface=MIXER,name='AIU ACODEC OUT EN Switch' numid=15,iface=MIXER,name='AIU ACODEC SRC' numid=14,iface=MIXER,name='AIU HDMI CTRL SRC' numid=13,iface=MIXER,name='AIU SPDIF SRC SEL' numid=12,iface=PCM,name='ELD',device=2 numid=11,iface=PCM,name='IEC958 Playback Default',device=2 numid=10,iface=PCM,name='IEC958 Playback Mask',device=2 numid=9,iface=PCM,name='Playback Channel Map',device=2
https://github.com/torvalds/linux/blob/master/arch/arm64/boot/dts/amlogic/me...
or on a Wetek Play 2:
WP2:~ # aplay -l **** List of PLAYBACK Hardware Devices **** card 0: WETEKPLAY2 [WETEK-PLAY2], device 0: fe.dai-link-0 (*) [] Subdevices: 1/1 Subdevice #0: subdevice #0 card 0: WETEKPLAY2 [WETEK-PLAY2], device 1: fe.dai-link-1 (*) [] Subdevices: 1/1 Subdevice #0: subdevice #0
WP2:~ # amixer controls numid=7,iface=MIXER,name='PCM Playback Volume' numid=6,iface=MIXER,name='AIU HDMI CTRL SRC' numid=5,iface=MIXER,name='AIU SPDIF SRC SEL' numid=4,iface=PCM,name='ELD',device=4 numid=3,iface=PCM,name='IEC958 Playback Default',device=4 numid=2,iface=PCM,name='IEC958 Playback Mask',device=4 numid=1,iface=PCM,name='Playback Channel Map',device=4
https://github.com/torvalds/linux/blob/master/arch/arm64/boot/dts/amlogic/me...
It looks like the PCM controls of the backend hdmi-codec are not routed through the DPCM driver the same way as PCM streams. We discussed that issue with Jerome, the driver author, but it’s not clear which bits we are missing. i.e. if it's something ASoC DPCM should be handling or if some further plumbing in the card driver or userspace is needed?
Any hints into the right direction would be highly appreciated!
Christian