[alsa-devel] 2 speakers are assigned to the same DAC, this can't support 4.0/2.1 channles

[Hui Wang]

On 06/11/2015 11:10 PM, Takashi Iwai wrote:
> At Wed, 10 Jun 2015 12:28:39 +0200,
> Takashi Iwai wrote:
>>>>> A cleaner way would be to prepare a different badness table for the
>>>>> speaker, and increase the value for shared_surr.  An untested patch is
>>>>> below.
>>>> Got it, I will test it soon. Thanks.
>>>>
>>> Hi Takashi,
>>>
>>> Your patch can fix the problem, it works very well.
>> OK, good to know.  I'd like to test a bit more via hda-emu whether
>> this gives any ill effects.  So far, this seems fixing a few other
>> machines, too, so it's a good thing to have in general.
> This change alone results in regressions on machines that are capable
> of 4.0/5.1 surrounds.  For avoiding it, the badness for multi-io has
> to be increased as well.  It's damn sensitive.
>
> But, now I wonder now whether blindly applying this is good.  Suppose
> a machine with 2.1 speaker and one headphone, but the codec has only
> two DACs.  With this setup, now the headphone and the speaker share
> the same DAC, as the cost of having individual 2.1 speaker volume.
> Is this more useful than having individual volumes for speaker and
> headphone?
If having individual volumes for speaker and headphone (the speakers 
share the same DAC), there will be no "Front Speaker" and "Bass 
Speaker", as a result, in the userspace, pulseaudio can't regard the 2.1 
channels is a valid profile.
>
> Maybe the machine you're trying to support has a different situation.
> So applying the new rule to limited devices is fine.  But if so, it's
> not necessarily to be an adjustment of badness table, but just you can
> provide the simple DAC/pin preference map explicitly in the fixup.
This is a good idea, so far this machine is the only one with this 
problem, it is suitable to use a machine specific fixup. If in future, 
we have more machines with this problem, then we will think about a 
general way to fix it.
>
>
> Takashi
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