ALSA: USB-audio: Add quirk for Zoom R16/24 playback

The Zoom R16/24 have a nonstandard playback format where each isochronous
packet contains a length descriptor in the first four bytes. (Curiously,
capture data does not contain this and requires no quirk.)

The quirk involves adding the extra length descriptor whenever outgoing
isochronous packets are generated, both in pcm.c (outgoing audio) and
endpoint.c (silent data).

In order to make the quirk as unintrusive as possible, for
pcm.c:prepare_playback_urb(), the isochronous packet descriptors are
initially set up in the same way no matter if the quirk is enabled or not.
Once it is time to actually copy the data into the outgoing packet buffer
(together with the added length descriptors) the isochronous descriptors
are adjusted in order take the increased payload length into account.

For endpoint.c:prepare_silent_urb() it makes more sense to modify the
actual function, partly because the function is less complex to start with
and partly because it is not as time-critical as prepare_playback_urb()
(whose bulk is run with interrupts disabled), so the (minute) additional
time spent in the non-quirk case is motivated by the simplicity of having
a single function for all cases.

The quirk is controlled by the new tx_length_quirk member in struct
snd_usb_substream and struct snd_usb_audio, which is conveyed to pcm.c
and endpoint.c from quirks.c in a similar manner to the txfr_quirk member
in the same structs.

In contrast to txfr_quirk however, the quirk is enabled directly in
quirks.c:create_standard_audio_quirk() by checking the USB ID in that
function. Another option would be to introduce a new
QUIRK_AUDIO_ZOOM_INTERFACE or somesuch, which would have made the quirk
very plain to see in the quirk table, but it was felt that the additional
code needed to implement it this way would just make the implementation
more complex with no real gain.

Tested with a Zoom R16, both by doing capture and playback separately
using arecord and aplay (8 channel capture and 2 channel playback,
respectively), as well as capture and playback together using Ardour, as
well as Audacity and Qtractor together with jackd.

The R24 is reportedly compatible with the R16 when used as an audio
interface. Both devices share the same USB ID and have the same number of
inputs (8) and outputs (2). Therefore "R16/24" is mentioned throughout the
patch.

Regression tested using an Edirol UA-5 in both class compliant (16-bit)
and "advanced" (24 bit, forces the use of quirks) modes.

Signed-off-by: Ricard Wanderlof <ricardw@axis.com>
Tested-by: Panu Matilainen <pmatilai@laiskiainen.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 31 insertions, 1 deletions

diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index e3c5bc0df69d..9245f52d43bd 100644
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -1409,6 +1409,32 @@ static void copy_to_urb(struct snd_usb_substream *subs, struct urb *urb,
 		subs->hwptr_done -= runtime->buffer_size * stride;
 }
 
+static unsigned int copy_to_urb_quirk(struct snd_usb_substream *subs,
+				      struct urb *urb, int stride,
+				      unsigned int bytes)
+{
+	__le32 packet_length;
+	int i;
+
+	/* Put __le32 length descriptor at start of each packet. */
+	for (i = 0; i < urb->number_of_packets; i++) {
+		unsigned int length = urb->iso_frame_desc[i].length;
+		unsigned int offset = urb->iso_frame_desc[i].offset;
+
+		packet_length = cpu_to_le32(length);
+		offset += i * sizeof(packet_length);
+		urb->iso_frame_desc[i].offset = offset;
+		urb->iso_frame_desc[i].length += sizeof(packet_length);
+		memcpy(urb->transfer_buffer + offset,
+		       &packet_length, sizeof(packet_length));
+		copy_to_urb(subs, urb, offset + sizeof(packet_length),
+			    stride, length);
+	}
+	/* Adjust transfer size accordingly. */
+	bytes += urb->number_of_packets * sizeof(packet_length);
+	return bytes;
+}
+
 static void prepare_playback_urb(struct snd_usb_substream *subs,
 				 struct urb *urb)
 {
@@ -1488,7 +1514,11 @@ static void prepare_playback_urb(struct snd_usb_substream *subs,
 			subs->hwptr_done -= runtime->buffer_size * stride;
 	} else {
 		/* usual PCM */
-		copy_to_urb(subs, urb, 0, stride, bytes);
+		if (!subs->tx_length_quirk)
+			copy_to_urb(subs, urb, 0, stride, bytes);
+		else
+			bytes = copy_to_urb_quirk(subs, urb, stride, bytes);
+			/* bytes is now amount of outgoing data */
 	}
 
 	/* update delay with exact number of samples queued */