[PATCH] usb-audio: don't use empty packets at start of playback

[PATCH] usb-audio: don't use empty packets at start of playback

[Clemens Ladisch]

Some widespread USB interface chips with adaptive iso endpoints hang
after receiving a series of empty packets when they expect data.  This
completely disables audio playback on those devices.  To avoid this, we
have to send packets containing silence (zero samples) instead.

ALSA bug: http://bugtrack.alsa-project.org/alsa-bug/view.php?id=1585

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>

Index: linux-2.6.15/sound/usb/usbaudio.c
===================================================================
--- linux-2.6.15.orig/sound/usb/usbaudio.c	2006-01-06 16:11:26.000000000 +0100
+++ linux-2.6.15/sound/usb/usbaudio.c	2006-01-11 19:29:18.000000000 +0100
@@ -480,22 +480,38 @@ static int retire_playback_sync_urb_hs(s
 /*
  * Prepare urb for streaming before playback starts.
  *
- * We don't care about (or have) any data, so we just send a transfer delimiter.
+ * We don't yet have data, so we send a frame of silence.
  */
 static int prepare_startup_playback_urb(snd_usb_substream_t *subs,
 					snd_pcm_runtime_t *runtime,
 					struct urb *urb)
 {
-	unsigned int i;
+	unsigned int i, offs, counts;
 	snd_urb_ctx_t *ctx = urb->context;
+	int stride = runtime->frame_bits >> 3;
 
+	offs = 0;
 	urb->dev = ctx->subs->dev;
 	urb->number_of_packets = subs->packs_per_ms;
 	for (i = 0; i < subs->packs_per_ms; ++i) {
-		urb->iso_frame_desc[i].offset = 0;
-		urb->iso_frame_desc[i].length = 0;
+		/* calculate the size of a packet */
+		if (subs->fill_max)
+			counts = subs->maxframesize; /* fixed */
+		else {
+			subs->phase = (subs->phase & 0xffff)
+				+ (subs->freqm << subs->datainterval);
+			counts = subs->phase >> 16;
+			if (counts > subs->maxframesize)
+				counts = subs->maxframesize;
+		}
+		urb->iso_frame_desc[i].offset = offs * stride;
+		urb->iso_frame_desc[i].length = counts * stride;
+		offs += counts;
 	}
-	urb->transfer_buffer_length = 0;
+	urb->transfer_buffer_length = offs * stride;
+	memset(urb->transfer_buffer,
+	       subs->cur_audiofmt->format == SNDRV_PCM_FORMAT_U8 ? 0x80 : 0,
+	       offs * stride);
 	return 0;
 }
 


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Re: [stable] [PATCH] usb-audio: don't use empty packets at start of playback

[Greg KH]

On Thu, Jan 12, 2006 at 09:44:29AM +0100, Clemens Ladisch wrote:
> Some widespread USB interface chips with adaptive iso endpoints hang
> after receiving a series of empty packets when they expect data.  This
> completely disables audio playback on those devices.  To avoid this, we
> have to send packets containing silence (zero samples) instead.
> 
> ALSA bug: http://bugtrack.alsa-project.org/alsa-bug/view.php?id=1585
> 
> Signed-off-by: Clemens Ladisch <clemens@ladisch.de>

Is this upstream in Linus's tree yet?  The Alsa cvs tree yet?

thanks,

greg k-h


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Re: [stable] [PATCH] usb-audio: don't use empty packets at start of playback

[Takashi Iwai]

At Thu, 12 Jan 2006 09:48:54 -0800,
Greg KH wrote:
> 
> On Thu, Jan 12, 2006 at 09:44:29AM +0100, Clemens Ladisch wrote:
> > Some widespread USB interface chips with adaptive iso endpoints hang
> > after receiving a series of empty packets when they expect data.  This
> > completely disables audio playback on those devices.  To avoid this, we
> > have to send packets containing silence (zero samples) instead.
> > 
> > ALSA bug: http://bugtrack.alsa-project.org/alsa-bug/view.php?id=1585
> > 
> > Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
> 
> Is this upstream in Linus's tree yet?  The Alsa cvs tree yet?

Already in ALSA CVS, so will be merged at the next pull request.


thanks,

Takashi


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Re: [stable] [PATCH] usb-audio: don't use empty packets at start of playback

[Chris Wright]

* Takashi Iwai (tiwai@suse.de) wrote:
> Already in ALSA CVS, so will be merged at the next pull request.

Thanks, queued to -stable.
-chris


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