ALSA: snd-usb: add quirks handler for DSD streams

Unfortunately, none of the UAC standards provides a way to identify DSD
(Direct Stream Digital) formats. Hence, this patch adds a quirks
handler to identify USB interfaces that are capable of handling DSD.

That quirks handler can augment the already parsed formats bit-field,
by any of the new SNDRV_PCM_FMTBIT_DSD_{U8_U16} and setting the dsd_dop
flag in the audio format, if the driver should take care for the DOP
byte stuffing.

The only devices that are known to work with this are the ones with
a 'Playback Designs' vendor id.
Signed-off-by: Daniel Mack <zonque@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/format.c

@@ -136,6 +136,9 @@ static u64 parse_audio_format_i_type(struct snd_usb_audio *chip,
 		snd_printk(KERN_INFO "%d:%u:%d : unsupported format bits %#x\n",
 			   chip->dev->devnum, fp->iface, fp->altsetting, format);
 	}
+
+	pcm_formats |= snd_usb_interface_dsd_format_quirks(chip, fp, sample_bytes);
+
 	return pcm_formats;
 }
 

sound/usb/quirks.c

@@ -916,3 +916,31 @@ void snd_usb_ctl_msg_quirk(struct usb_device *dev, unsigned int pipe,
 		mdelay(20);
 }
 
+/*
+ * snd_usb_interface_dsd_format_quirks() is called from format.c to
+ * augment the PCM format bit-field for DSD types. The UAC standards
+ * don't have a designated bit field to denote DSD-capable interfaces,
+ * hence all hardware that is known to support this format has to be
+ * listed here.
+ */
+u64 snd_usb_interface_dsd_format_quirks(struct snd_usb_audio *chip,
+					struct audioformat *fp,
+					unsigned int sample_bytes)
+{
+	/* Playback Designs */
+	if (le16_to_cpu(chip->dev->descriptor.idVendor) == 0x23ba) {
+		switch (fp->altsetting) {
+		case 1:
+			fp->dsd_dop = true;
+			return SNDRV_PCM_FMTBIT_DSD_U16_LE;
+		case 2:
+			fp->dsd_bitrev = true;
+			return SNDRV_PCM_FMTBIT_DSD_U8;
+		case 3:
+			fp->dsd_bitrev = true;
+			return SNDRV_PCM_FMTBIT_DSD_U16_LE;
+		}
+	}
+
+	return 0;
+}

sound/usb/quirks.h

@@ -31,4 +31,8 @@ void snd_usb_ctl_msg_quirk(struct usb_device *dev, unsigned int pipe,
 			   __u8 request, __u8 requesttype, __u16 value,
 			   __u16 index, void *data, __u16 size);
 
+u64 snd_usb_interface_dsd_format_quirks(struct snd_usb_audio *chip,
+					struct audioformat *fp,
+					unsigned int sample_bytes);
+
 #endif /* __USBAUDIO_QUIRKS_H */