[alsa-devel] [PATCH 0/3] ALSA: snd-usb: Some small fixes to make Playback Design products work

Jussi Laako jussi at sonarnerd.net
Sun Mar 24 11:50:57 CET 2013

On 03/24/2013 03:50 AM, Andreas Koch wrote:
> rate for PCM. If you plug that DAC into a Mac, the Mac will
> automatically select 705.6kHz for PCM and then nothing will work because
> the DAC doesn't support that in PCM. So then, the DAC would have to
> define 2 complete interfaces: one for PCM and one for DSD. That

OK, the difference is that I don't use UAC2 at all, but completely 
different protocol. So what I'm talking about is only how it looks from 
the driver towards the application...

DoP could be implemented similar way inside the UAC driver using for 
example snd_pcm_hw_rule_add() between SNDRV_PCM_HW_PARAM_FORMAT and 
SNDRV_PCM_HW_PARAM_RATE. And maybe enabled as quirks?

There are many devices having constraints between rate and channels. In 
this case we just have a constraint between rate and formats.

Looking at the UAC driver there seems to be something a bit related:
                 /* FIXME: there is no AC3 format defined yet */
                 // fp->formats = SNDRV_PCM_FMTBIT_AC3;
                 fp->formats = SNDRV_PCM_FMTBIT_U8; /* temporary hack to 
  byte streams */

	- Jussi

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