ALSA: usb-audio: relax urb data align. restriction HVR-950Q and HVR-850 only

Addressing audio quality problem.

In sound/usb/usbaudio.c, for the Hauppage HVR-950Q and HVR-850 only, change
retire_capture_urb to allow transfers on audio sub-slot boundaries rather
than audio slots boundaries.

With these devices the left and right channel samples can be split between
two different urbs. Throwing away extra channel samples causes a sound
quality problem for stereo streams as the left and right channels are
swapped repeatedly, perhaps many times per second.

Urbs unaligned on sub-slot boundaries are still truncated to the next
lowest stride (audio slot) to retain synchronization on samples even
though left/right channel synchronization may be lost in this case.

Detect the quirk using a case statement in snd_usb_audio_probe.

BugLink: https://bugs.launchpad.net/ubuntu/+bug/495745

Signed-off-by: John S. Gruber <JohnSGruber@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

2 files changed, 30 insertions, 2 deletions

diff --git a/sound/usb/usbaudio.c b/sound/usb/usbaudio.c
index 8fcb5d5a94b6..617515f6ec7b 100644
--- a/sound/usb/usbaudio.c
+++ b/sound/usb/usbaudio.c
@@ -169,6 +169,7 @@ struct snd_usb_substream {
         unsigned int curpacksize;       /* current packet size in bytes (for capture) */
         unsigned int curframesize;      /* current packet size in frames (for capture) */
         unsigned int fill_max: 1;       /* fill max packet size always */
+        unsigned int txfr_quirk:1;      /* allow sub-frame alignment */
         unsigned int fmt_type;          /* USB audio format type (1-3) */
 
         unsigned int running: 1;        /* running status */
@@ -353,14 +354,25 @@ static int retire_capture_urb(struct snd_usb_substream *subs,
                         snd_printd(KERN_ERR "frame %d active: %d\n", i, urb->iso_frame_desc[i].status);
                         // continue;
                 }
-                frames = urb->iso_frame_desc[i].actual_length / stride;
-                bytes = frames * stride;
+                bytes = urb->iso_frame_desc[i].actual_length;
+                frames = bytes / stride;
+                if (!subs->txfr_quirk)
+                        bytes = frames * stride;
+                if (bytes % (runtime->sample_bits >> 3) != 0) {
+#ifdef CONFIG_SND_DEBUG_VERBOSE
+                        int oldbytes = bytes;
+#endif
+                        bytes = frames * stride;
+                        snd_printdd(KERN_ERR "Corrected urb data len. %d->%d\n",
+                                                        oldbytes, bytes);
+                }
                 /* update the current pointer */
                 spin_lock_irqsave(&subs->lock, flags);
                 oldptr = subs->hwptr_done;
                 subs->hwptr_done += bytes;
                 if (subs->hwptr_done >= runtime->buffer_size * stride)
                         subs->hwptr_done -= runtime->buffer_size * stride;
+                frames = (bytes + (oldptr % stride)) / stride;
                 subs->transfer_done += frames;
                 if (subs->transfer_done >= runtime->period_size) {
                         subs->transfer_done -= runtime->period_size;
@@ -2238,6 +2250,7 @@ static void init_substream(struct snd_usb_stream *as, int stream, struct audiofo
         subs->stream = as;
         subs->direction = stream;
         subs->dev = as->chip->dev;
+        subs->txfr_quirk = as->chip->txfr_quirk;
         if (snd_usb_get_speed(subs->dev) == USB_SPEED_FULL) {
                 subs->ops = audio_urb_ops[stream];
         } else {
@@ -3618,6 +3631,20 @@ static void *snd_usb_audio_probe(struct usb_device *dev,
                 }
         }
 
+        switch (chip->usb_id) {
+        case USB_ID(0x2040, 0x7200): /* Hauppage hvr950Q */
+        case USB_ID(0x2040, 0x7221): /* Hauppage hvr950Q */
+        case USB_ID(0x2040, 0x7222): /* Hauppage hvr950Q */
+        case USB_ID(0x2040, 0x7223): /* Hauppage hvr950Q */
+        case USB_ID(0x2040, 0x7224): /* Hauppage hvr950Q */
+        case USB_ID(0x2040, 0x7225): /* Hauppage hvr950Q */
+        case USB_ID(0x2040, 0x7230): /* Hauppage hvr850 */
+        case USB_ID(0x2040, 0x7250): /* Hauppage hvr950Q */
+                chip->txfr_quirk = 1;
+                break;
+        default:
+                chip->txfr_quirk = 0;
+                }
         err = 1; /* continue */
         if (quirk && quirk->ifnum != QUIRK_NO_INTERFACE) {
                 /* need some special handlings */
diff --git a/sound/usb/usbaudio.h b/sound/usb/usbaudio.h
index 152216738cce..d180554b81f0 100644
--- a/sound/usb/usbaudio.h
+++ b/sound/usb/usbaudio.h
@@ -125,6 +125,7 @@ struct snd_usb_audio {
         struct snd_card *card;
         u32 usb_id;
         int shutdown;
+        unsigned int txfr_quirk:1; /* Subframe boundaries on transfers */
         int num_interfaces;
         int num_suspended_intf;