From mboxrd@z Thu Jan  1 00:00:00 1970
From: Clemens Ladisch <clemens@ladisch.de>
Subject: Re: [PATCH 1/5] ALSA: snd-usb: implement new endpoint
 streaming model
Date: Wed, 02 Nov 2011 11:26:37 +0100
Message-ID: <4EB11ADD.2090701@ladisch.de>
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To: Daniel Mack <zonque@gmail.com>
Cc: tiwai@suse.de, blablack@gmail.com, alsa-devel@alsa-project.org, gdiffey@gmail.com, linuxaudio@showlabor.de
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Daniel Mack wrote:
> +void snd_usb_handle_sync_urb(struct snd_usb_endpoint *ep,
> +{
> +	if (snd_usb_endpoint_implict_feedback_sink(ep) && ep->use_count > 0) {
>  		...
> +		for (i = 0; i < ep->nurbs; i++)
> +			if (!test_and_set_bit(i, &ep->active_mask)) {
> +				out_urb = ep->urb[i].urb;
> +				break;
> +			}
> +
> +		if (!out_urb) {
> +			snd_printk(KERN_ERR "Unable to find an urb for playback (nurbs %d)\n",
> +				   ep->nurbs);

AFAICS the driver tries for all URBS to be queued at all times.
So if the HC driver completes a sync URB before the corresponding
playback URB, it may be possible for this error to happen.


Regards,
Clemens