Hi,
these are some tentative patches to allow sound drivers to provide routing information to userspace. (So far, snd-usb-audio has a partial implementation; I haven't yet had time for snd-hda-intel. I haven't even looked at ASoC.)
The media controller API <linux/media.h> allows prividing routing information, but its implementation does not quite fit the sound drivers: * it allows reconfiguration of links, but not in a way that would be useful for ALSA selector controls; * it allows drivers to access the entity graph and pipelines, which is not needed; * it is rather heavyweight.
Therefore, these patches create their own implementation of the media controller API. In this implementation, all entity and link information is completely static, and more space-efficient.
For simplicity, the ioctls hook into the ALSA control device instead of creating a new /dev/media* device.
The separate implementation does not allow sharing of one media controller device in the case of combined audio/video devices. However, separate drivers would already be a problem for HDMI outputs (GPU and sound); it appears we might need some mechanism to connect the topologies of multiple media devices.
TLVs (for jack entities, and for associating controls with entities) are not yet defined.
Example output for my simple UA-1A device (not all information is decoded correctly):
$ media-ctl -p -d /dev/snd/controlC5 Opening media device /dev/snd/controlC5 Enumerating entities Found 4 entities Enumerating pads and links Media controller API version 0.0.0
Media device information ------------------------ driver snd-usb-audio model EDIROL UA-1A serial bus info usb-0000:00:12.2-4.3 hw revision 0x101 driver version 0.0.0
Device topology - entity 1: USB Audio (1 pad, 1 link) type Node subtype ALSA device node name /dev/tty (should be hw:5,0,0) pad0: Source -> "OT3":0 [ENABLED,IMMUTABLE]
- entity 3: OT3 (1 pad, 1 link) type Unknown subtype Unknown (should be Jack) pad0: Sink <- "USB Audio":0 [ENABLED,IMMUTABLE]
- entity 4: IT4 (1 pad, 1 link) type Unknown subtype Unknown pad0: Source -> "USB Audio":0 [ENABLED,IMMUTABLE]
- entity 7: USB Audio (1 pad, 1 link) type Node subtype ALSA device node name /dev/tty pad0: Sink <- "IT4":0 [ENABLED,IMMUTABLE]
include/linux/media.h | 9 include/sound/core.h | 13 + include/sound/media.h | 116 ++++++++++ include/sound/pcm.h | 6 sound/core/Kconfig | 7 sound/core/Makefile | 1 sound/core/init.c | 4 sound/core/media.c | 425 ++++++++++++++++++++++++++++++++++++++ sound/core/pcm.c | 46 ++++ sound/core/sound.c | 3 sound/pci/hda/hda_intel.c | 2 sound/usb/card.c | 2 sound/usb/mixer.c | 278 ++++++++++++++++++++++++ sound/usb/quirks.c | 4 sound/usb/stream.c | 16 - sound/usb/stream.h | 1 16 files changed, 925 insertions(+), 8 deletions(-)
Regards, Clemens