[alsa-devel] [PATCH 1/2] ALSA: usb: fix corrupted pointers due to interface setting change

[Takashi Iwai]

On Fri, 14 Aug 2015 00:42:32 +0200,
Pierre-Louis Bossart wrote:
> 
> When a transition occurs between alternate settings that do not use the
> same synchronization method, the substream pointers were not reset.
> This prevents audio from being played during the second transition.
> 
> Identified and tested with M-Audio Transit device
> (0763:2006 Midiman M-Audio Transit)

Hmm, I have this old device, too, but couldn't reproduce the problem.
Is there any special setup with it?


Takashi

> 
> Details of the issue:
> 
> First playback to adaptive endpoint:
> $ aplay -Dhw:1,0 ~/24_96.wav
> Playing WAVE '/home/plb/24_96.wav' : Signed 24 bit Little Endian in 3bytes,
> Rate 96000 Hz, Stereo
> 
> [ 3169.297556] usb 1-2: setting usb interface 1:1
> [ 3169.297568] usb 1-2: Creating new playback data endpoint #3
> [ 3169.298563] usb 1-2: Setting params for ep #3 (type 0, 3 urbs), ret=0
> [ 3169.298574] usb 1-2: Starting data EP @ffff880035fc8000
> 
> first playback to asynchronous endpoint:
> $ aplay -Dhw:1,0 ~/16_48.wav
> Playing WAVE '/home/plb/16_48.wav' : Signed 16 bit Little Endian,
> Rate 48000 Hz, Stereo
> 
> [ 3204.520251] usb 1-2: setting usb interface 1:3
> [ 3204.520264] usb 1-2: Creating new playback data endpoint #3
> [ 3204.520272] usb 1-2: Creating new capture sync endpoint #83
> [ 3204.521162] usb 1-2: Setting params for ep #3 (type 0, 4 urbs), ret=0
> [ 3204.521177] usb 1-2: Setting params for ep #83 (type 1, 4 urbs), ret=0
> [ 3204.521182] usb 1-2: Starting data EP @ffff880035fce000
> [ 3204.521204] usb 1-2: Starting sync EP @ffff8800bd616000
> 
> second playback to adaptive endpoint: no audio and error on terminal:
> $ aplay -Dhw:1,0 ~/24_96.wav
> Playing WAVE '/home/plb/24_96.wav' : Signed 24 bit Little Endian in 3bytes,
> Rate 96000 Hz, Stereo
> aplay: pcm_write:1939: write error: Input/output error
> 
> [ 3239.483589] usb 1-2: setting usb interface 1:1
> [ 3239.483601] usb 1-2: Re-using EP 3 in iface 1,1 @ffff880035fc8000
> [ 3239.484590] usb 1-2: Setting params for ep #3 (type 0, 4 urbs), ret=0
> [ 3239.484606] usb 1-2: Setting params for ep #83 (type 1, 4 urbs), ret=0
> 
> This last line shows that a sync endpoint is used when it shouldn't.
> The sync endpoint is no longer valid and the pointers are corrupted
> 
> Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>
> ---
>  sound/usb/pcm.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
> index b4ef410..7cd7c03 100644
> --- a/sound/usb/pcm.c
> +++ b/sound/usb/pcm.c
> @@ -395,6 +395,19 @@ static int set_sync_endpoint(struct snd_usb_substream *subs,
>  	if (err < 0)
>  		return err;
>  
> +	if ((is_playback && (attr != USB_ENDPOINT_SYNC_ASYNC)) ||
> +		(!is_playback && (attr != USB_ENDPOINT_SYNC_ADAPTIVE))) {
> +
> +		/*
> +		 * Clean-up subs pointers to make sure sync_endpoint is never
> +		 * configured. This is needed in case of a transition between
> +		 * alternate settings using different synchronization modes
> +		 * where the previous sync_endpoint may no longer be valid.
> +		 */
> +		subs->sync_endpoint = NULL;
> +		subs->data_endpoint->sync_master = NULL;
> +	}
> +
>  	if (altsd->bNumEndpoints < 2)
>  		return 0;
>  
> -- 
> 1.9.1
>