[alsa-devel] [PATCH v2] add native DSD support for XMOS based DACs

[Jurgen Kramer]

On Fri, 2014-09-05 at 16:27 +0200, Takashi Iwai wrote:
> At Fri, 05 Sep 2014 15:58:39 +0200,
> Jurgen Kramer wrote:
> > 
> > On Fri, 2014-09-05 at 15:36 +0200, Takashi Iwai wrote:
> > > At Fri,  5 Sep 2014 14:24:57 +0200,
> > > Jurgen Kramer wrote:
> > > > 
> > > > Add quirks for XMOS based DACs for native DSD playback support using the new
> > > > DSD_U32_LE sample format.
> > > > 
> > > > This version adds native DSD support for:
> > > > - iFi Audio micro iDSD/nano iDSD (they use the same prod. id)
> > > > - DIYINHK USB to I2S/DSD converter
> > > > 
> > > > Changes from v1:
> > > > - use specific product id and alt setting per XMOS based device
> > > > 
> > > > Signed-off-by: Jurgen Kramer <gtmkramer at xs4all.nl>
> > > > ---
> > > >  sound/usb/quirks.c | 15 +++++++++++++++
> > > >  1 file changed, 15 insertions(+)
> > > > 
> > > > diff --git a/sound/usb/quirks.c b/sound/usb/quirks.c
> > > > index 19a921e..5ae0536 100644
> > > > --- a/sound/usb/quirks.c
> > > > +++ b/sound/usb/quirks.c
> > > > @@ -1174,5 +1174,20 @@ u64 snd_usb_interface_dsd_format_quirks(struct snd_usb_audio *chip,
> > > >  		}
> > > >  	}
> > > >  
> > > > +	/* XMOS based USB DACs */
> > > > +	if (le16_to_cpu(chip->dev->descriptor.idVendor) == 0x20b1) {
> > > > +		switch (le16_to_cpu(chip->dev->descriptor.idProduct)) {
> > > > +		/* iFi Audio micro/nano iDSD */
> > > > +		case 0x3008:
> > > > +			if (fp->altsetting == 2)
> > > > +				return SNDRV_PCM_FMTBIT_DSD_U32_LE;
> > > 
> > > Missing break?
> > It is already returning. Where would the break go?
> 
> What if fp->altsetting == 3 with 20b1:3008 chip?
> Then it falls down to below, and return SNDRV_PCM_FMTBIT_DSD_U32_LE.
> Is this expected?
With fp->altsetting == 3 for 20b1:3008 I do not see it returning
SNDRV_PCM_FMTBIT_DSD_U32_LE, it falls through to 'return 0'.

However, would this be more appropriate/readable?:

case 0x3008:
	if (fp->altsetting == 2)
		return SNDRV_PCM_FMTBIT_DSD_U32_LE;
	else
		break;

or even:

case 0x3008:
	if (fp->altsetting == 2)
		return SNDRV_PCM_FMTBIT_DSD_U32_LE;
	else
		return 0;

> > > 
> > > > +		/* DIYINHK DSD DXD 384kHz USB to I2S/DSD */
> > > > +		case 0x2009:
> > > > +			if (fp->altsetting == 3)
> > > > +				return SNDRV_PCM_FMTBIT_DSD_U32_LE;
> > > 
> > > Ditto.
> > See above.
> 
> If the fallthrough is intentional, you *must* put a comment it's
> really a fallthrough.
> 
> 
Jurgen