Re: native DSD on PCI linux driver

[Takashi Iwai <tiwai@suse.de>]

On Tue, 03 Dec 2024 13:31:03 +0100,
Takashi Iwai wrote:
> 
> On Tue, 26 Nov 2024 10:41:21 +0100,
> Filip Van Lunteren wrote:
> > 
> > 
> > Hello,
> > 
> > I am currently developing PCI audio output hardware and driver and want to
> > integrate native DSD playback. I am struggling to find documentation on this.
> > Is there DSD native support in ALSA? And how do I incorporate it? PCM is
> > already set up and works.
> 
> AFAIK, in the driver side, there is not much special; it assumes that
> DSD samples are passed over the standard PCM stream, and the driver
> uses special formats SNDRV_PCM_FORMAT_DSD_U8, *_U16 and *_U32 (with
> _LE and _BE suffix) for 8, 16 and 32bit, instead of the standard
> SNDRV_PCM_FORMAT_U8, *_S16, etc.  For those formats, the silence data
> is assumed to be 0x69, 0x6969, etc.

To be more exactly, the above statement is about PCM core.

Most of DSD stuff is found in USB audio driver, and if you need a DoP
support, the driver has to convert it manually.
(We may push it to PCM core, once when needed, but as currently it's 
required only by USB-audio, it's locally handled.)

Similarly, there is also bit-reversed transfer for some devices.

Both can be found in sound/usb/pcm.c.


HTH,

Takashi