[PATCH v2] ALSA: usb-audio: Re-add sample rate quirk for Pioneer DJM-750

[Olivia Mackintosh <livvy@base.nu>]

Re-add the sample-rate quirk originally implemented by Dmitry
Panchenko for the DJM-900NXS2 but for the DJM-750.  This commit only
adds it again for the DJM-750 since I can only verify that it is
absolutely required for this device. Other models may need this patch
but I'm hesitant to add them as I cannot test.

The 'wIndex' is passed literally in the function call as we cannot
derive this from 'fmt->sync_ep' due to it not being set.  We can change
this if and when we revisit implicit FB.

Signed-off-by: Olivia Mackintosh <livvy@base.nu>
---
 sound/usb/quirks.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/sound/usb/quirks.c b/sound/usb/quirks.c
index e196e364cef1..b49a66f863f3 100644
--- a/sound/usb/quirks.c
+++ b/sound/usb/quirks.c
@@ -1470,6 +1470,23 @@ static void set_format_emu_quirk(struct snd_usb_substream *subs,
 	subs->pkt_offset_adj = (emu_samplerate_id >= EMU_QUIRK_SR_176400HZ) ? 4 : 0;
 }
 
+static int pioneer_djm_set_format_quirk(struct snd_usb_substream *subs,
+					u16 windex)
+{
+	unsigned int cur_rate = subs->data_endpoint->cur_rate;
+	u8 sr[3];
+	// Convert to little endian
+	sr[0] = cur_rate&0xff;
+	sr[1] = (cur_rate>>8)&0xff;
+	sr[2] = (cur_rate>>16)&0xff;
+	usb_set_interface(subs->dev, 0, 1);
+	// we should derive windex from fmt-sync_ep but it's not set
+	snd_usb_ctl_msg(subs->stream->chip->dev,
+		usb_rcvctrlpipe(subs->stream->chip->dev, 0),
+		0x01, 0x22, 0x0100, windex, &sr, 0x0003);
+	return 0;
+}
+
 void snd_usb_set_format_quirk(struct snd_usb_substream *subs,
 			      const struct audioformat *fmt)
 {
@@ -1483,6 +1500,9 @@ void snd_usb_set_format_quirk(struct snd_usb_substream *subs,
 	case USB_ID(0x534d, 0x2109): /* MacroSilicon MS2109 */
 		subs->stream_offset_adj = 2;
 		break;
+	case USB_ID(0x08e4, 0x017f): /* Pioneer DJM-750 */
+		pioneer_djm_set_format_quirk(subs, 0x0086);
+		break;
 	}
 }
 
-- 
2.30.0