[pulseaudio-discuss] [PATCH v2] alsa: Add support for sound cards with 4-channel input.

David Henningsson david.henningsson at canonical.com
Mon May 7 13:02:00 PDT 2012

2012-05-07 03:47, Tanu Kaskinen skrev:
> On Mon, 2012-05-07 at 09:46 +0530, Arun Raghavan wrote:
>> On Tue, 2012-05-01 at 20:09 +0300, Tanu Kaskinen wrote:
>>> Changes in v2:
>>>   - Call the mapping a generic 4-channel input mapping
>>>     instead of a 4-channel mic array mapping. The mapping
>>>     will be used also by sound cards that have two stereo
>>>     input jacks, so in those cases talking about mic arrays
>>>     is wrong.
>>>   - Added a comment about using the "hw" device name.
>>> BugLink: https://bugs.freedesktop.org/show_bug.cgi?id=45813
>>> ---
>>>   src/modules/alsa/alsa-mixer.c                    |    1 +
>>>   src/modules/alsa/mixer/profile-sets/default.conf |    9 +++++++++
>>>   2 files changed, 10 insertions(+)
>>> diff --git a/src/modules/alsa/alsa-mixer.c b/src/modules/alsa/alsa-mixer.c
>>> index abb12ee..8b54f75 100644
>>> --- a/src/modules/alsa/alsa-mixer.c
>>> +++ b/src/modules/alsa/alsa-mixer.c
>>> @@ -3888,6 +3888,7 @@ static int mapping_verify(pa_alsa_mapping *m, const pa_channel_map *bonus) {
>>>           { "analog-surround-61",     N_("Analog Surround 6.1") },
>>>           { "analog-surround-70",     N_("Analog Surround 7.0") },
>>>           { "analog-surround-71",     N_("Analog Surround 7.1") },
>>> +        { "analog-4-channel-input", N_("Analog 4-channel Input") },
>> Since this is limited to some specific hardware, shouldn't we set up
>> udev rules instead of always probing?
> "All devices supporting 4-channel input" isn't very specific hardware

I agree with Arun on this one. Besides, it is not obvious to me what the 
channel mapping should be either, and couldn't that vary between 
different 4-channel hardware? Is the aux* just causing all inputs to be 
added for whatever the client wants to have...?

> and I doubt udev can be used to query the amount of supported
> channels.
Hmm...that raises a thought I didn't consider before. Why don't we do 
this in alsa-lib? If this varies between devices, we could create e g, 
for 4-channel mic hardware A, we set up a alsa-lib ttable to have 
"front" record two channels, the two left ones mixing in to the left and 
the two right ones mixing into the right. Or in what way do we actually 
use all four channels today?

> But if you think that the new mapping really causes too much
> overhead for the common case, I can live with udev rules too
It depends on the number of 4-channel mics out there. If it's just 
kinect and one more, I think udev rules are better. If we have 20 
different brands all working the same, it would be worth it.

// David

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