[PATCH 5.8 406/464] ALSA: usb-audio: work around streaming quirk for MacroSilicon MS2109

[Greg Kroah-Hartman]

From: Hector Martin <marcan@xxxxxxxxx>

commit 1b7ecc241a67ad6b584e071bd791a54e0cd5f097 upstream.

Further investigation of the L-R swap problem on the MS2109 reveals that
the problem isn't that the channels are swapped, but rather that they
are swapped and also out of phase by one sample. In other words, the
issue is actually that the very first frame that comes from the hardware
is a half-frame containing only the right channel, and after that
everything becomes offset.

So introduce a new quirk field to drop the very first 2 bytes that come
in after the format is configured and a capture stream starts. This puts
the channels in phase and in the correct order.

Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Hector Martin <marcan@xxxxxxxxx>
Link: https://lore.kernel.org/r/20200810082400.225858-1-marcan@xxxxxxxxx
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 sound/usb/card.h   |    1 +
 sound/usb/pcm.c    |    6 ++++++
 sound/usb/quirks.c |    3 +++
 sound/usb/stream.c |    1 +
 4 files changed, 11 insertions(+)

--- a/sound/usb/card.h
+++ b/sound/usb/card.h
@@ -137,6 +137,7 @@ struct snd_usb_substream {
 	unsigned int tx_length_quirk:1;	/* add length specifier to transfers */
 	unsigned int fmt_type;		/* USB audio format type (1-3) */
 	unsigned int pkt_offset_adj;	/* Bytes to drop from beginning of packets (for non-compliant devices) */
+	unsigned int stream_offset_adj;	/* Bytes to drop from beginning of stream (for non-compliant devices) */
 
 	unsigned int running: 1;	/* running status */
 
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -1420,6 +1420,12 @@ static void retire_capture_urb(struct sn
 			// continue;
 		}
 		bytes = urb->iso_frame_desc[i].actual_length;
+		if (subs->stream_offset_adj > 0) {
+			unsigned int adj = min(subs->stream_offset_adj, bytes);
+			cp += adj;
+			bytes -= adj;
+			subs->stream_offset_adj -= adj;
+		}
 		frames = bytes / stride;
 		if (!subs->txfr_quirk)
 			bytes = frames * stride;
--- a/sound/usb/quirks.c
+++ b/sound/usb/quirks.c
@@ -1495,6 +1495,9 @@ void snd_usb_set_format_quirk(struct snd
 	case USB_ID(0x2b73, 0x000a): /* Pioneer DJ DJM-900NXS2 */
 		pioneer_djm_set_format_quirk(subs);
 		break;
+	case USB_ID(0x534d, 0x2109): /* MacroSilicon MS2109 */
+		subs->stream_offset_adj = 2;
+		break;
 	}
 }
 
--- a/sound/usb/stream.c
+++ b/sound/usb/stream.c
@@ -94,6 +94,7 @@ static void snd_usb_init_substream(struc
 	subs->tx_length_quirk = as->chip->tx_length_quirk;
 	subs->speed = snd_usb_get_speed(subs->dev);
 	subs->pkt_offset_adj = 0;
+	subs->stream_offset_adj = 0;
 
 	snd_usb_set_pcm_ops(as->pcm, stream);