[alsa-devel] [PATCH] ALSA: usb: use multiple packets per urb for Wireless USB inbound audio

[Takashi Iwai]

At Tue, 26 Nov 2013 13:58:15 -0600,
Thomas Pugliese wrote:
> 
> For Wireless USB audio devices, use multiple isoc packets per URB for
> inbound endpoints with a datainterval < 5.  This allows the WUSB host
> controller to take advantage of bursting to service endpoints whose
> logical polling interval is less than the 4ms minimum polling interval
> limit in WUSB.
> 
> Signed-off-by: Thomas Pugliese <thomas.pugliese at gmail.com>

Thanks, applied now.


Takashi

> ---
>  sound/usb/endpoint.c |   16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c
> index b9ba0fc..83aabea2 100644
> --- a/sound/usb/endpoint.c
> +++ b/sound/usb/endpoint.c
> @@ -636,8 +636,22 @@ static int data_ep_set_params(struct snd_usb_endpoint *ep,
>  	if (usb_pipein(ep->pipe) ||
>  			snd_usb_endpoint_implicit_feedback_sink(ep)) {
>  
> +		urb_packs = packs_per_ms;
> +		/*
> +		 * Wireless devices can poll at a max rate of once per 4ms.
> +		 * For dataintervals less than 5, increase the packet count to
> +		 * allow the host controller to use bursting to fill in the
> +		 * gaps.
> +		 */
> +		if (snd_usb_get_speed(ep->chip->dev) == USB_SPEED_WIRELESS) {
> +			int interval = ep->datainterval;
> +			while (interval < 5) {
> +				urb_packs <<= 1;
> +				++interval;
> +			}
> +		}
>  		/* make capture URBs <= 1 ms and smaller than a period */
> -		urb_packs = min(max_packs_per_urb, packs_per_ms);
> +		urb_packs = min(max_packs_per_urb, urb_packs);
>  		while (urb_packs > 1 && urb_packs * maxsize >= period_bytes)
>  			urb_packs >>= 1;
>  		ep->nurbs = MAX_URBS;
> -- 
> 1.7.10.4
> 
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