Re: Quirks for MacroSilicon MS2100/MS2106

[Jaroslav Kysela <perex@perex.cz>]

On 23. 06. 22 7:58, Takashi Iwai wrote:

>> Even with this patch, there is a remaining problem, which is not present
>> in the MS2109. The sound sample values range from 0x0000 to 0x7fff, with
>> silence around 0x4000, i.e. 15-bit-ish audio. This actually sounds OK to
>> the ear (although half as loud as it should be), but looks odd when
>> looking at the waveform, and makes volume meters always think the sound
>> is very loud.
>>
>> To convert to s16le, I can bitshift one bit left, and subtract 32768.
>> I'm told that this isn't something that can or should be done in the
>> kernel, but should be in userspace. Any more advice on how to fix this
>> remaining quirk would be very welcome.
> 
> Ouch, this is painful.  We haven't had any devices that require a
> 15 bit unsigned format, and maybe we don't want to add it to the
> common standard format just for one funky device, either.  Such data
> processing could be done in alsa-lib, but for the proper interaction
> with the user-space, the kernel should provide some information so
> that user-space can process the data accordingly.  However, we have no
> proper way defined for it generically, so far.
> 
> Maybe an easy way would be to create an alsa-lib external plugin, and
> apply it per device.  Jaroslav, could it be done via UCM?

I agree that we may start with a special plugin for this format. The UCM can 
use any alsa-lib configuration now. So PA/PW should work with this very 
specific hardware when properly configured.

Note that we have SNDRV_PCM_FORMAT_SPECIAL for such cases. It will imply that 
the applications will fail when the special conversion plugin is not used. The 
minor issue may be with the silence routines (which is already with the 
improper format).

					Jaroslav

-- 
Jaroslav Kysela <perex@perex.cz>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.