Commit d215f63d authored by Takashi Iwai's avatar Takashi Iwai
Browse files

ALSA: usb-audio: Check available frames for the next packet size 

This is yet more preparation for the upcoming changes.

Extend snd_usb_endpoint_next_packet_size() to check the available
frames and return -EAGAIN if the next packet size is equal or exceeds
the given size.  This will be needed for avoiding XRUN during the low
latency operation.

As of this patch, avail=0 is passed, i.e. the check is skipped and no
behavior change.

Link: https://lore.kernel.org/r/20210929080844.11583-7-tiwai@suse.de


Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent bceee753

sound/usb/endpoint.c

+36 −15
Original line number Diff line number Diff line
@@ -148,18 +148,23 @@ int snd_usb_endpoint_implicit_feedback_sink(struct snd_usb_endpoint *ep) 
 * This won't be used for implicit feedback which takes the packet size

 * returned from the sync source

 */

static int slave_next_packet_size(struct snd_usb_endpoint *ep)

static int slave_next_packet_size(struct snd_usb_endpoint *ep,

				  unsigned int avail)

{

	unsigned long flags;

	unsigned int phase;

	int ret;



	if (ep->fill_max)

		return ep->maxframesize;



	spin_lock_irqsave(&ep->lock, flags);

	ep->phase = (ep->phase & 0xffff)

		+ (ep->freqm << ep->datainterval);

	ret = min(ep->phase >> 16, ep->maxframesize);

	phase = (ep->phase & 0xffff) + (ep->freqm << ep->datainterval);

	ret = min(phase >> 16, ep->maxframesize);

	if (avail && ret >= avail)

		ret = -EAGAIN;

	else

		ep->phase = phase;

	spin_unlock_irqrestore(&ep->lock, flags);



	return ret;
@@ -169,20 +174,25 @@ static int slave_next_packet_size(struct snd_usb_endpoint *ep) 
 * Return the number of samples to be sent in the next packet

 * for adaptive and synchronous endpoints

 */

static int next_packet_size(struct snd_usb_endpoint *ep)

static int next_packet_size(struct snd_usb_endpoint *ep, unsigned int avail)

{

	unsigned int sample_accum;

	int ret;



	if (ep->fill_max)

		return ep->maxframesize;



	ep->sample_accum += ep->sample_rem;

	if (ep->sample_accum >= ep->pps) {

		ep->sample_accum -= ep->pps;

	sample_accum += ep->sample_rem;

	if (sample_accum >= ep->pps) {

		sample_accum -= ep->pps;

		ret = ep->packsize[1];

	} else {

		ret = ep->packsize[0];

	}

	if (avail && ret >= avail)

		ret = -EAGAIN;

	else

		ep->sample_accum = sample_accum;



	return ret;

}
@@ -190,16 +200,27 @@ static int next_packet_size(struct snd_usb_endpoint *ep) 
/*

 * snd_usb_endpoint_next_packet_size: Return the number of samples to be sent

 * in the next packet

 *

 * If the size is equal or exceeds @avail, don't proceed but return -EAGAIN

 * Exception: @avail = 0 for skipping the check.

 */

int snd_usb_endpoint_next_packet_size(struct snd_usb_endpoint *ep,

				      struct snd_urb_ctx *ctx, int idx)

				      struct snd_urb_ctx *ctx, int idx,

				      unsigned int avail)

{

	if (ctx->packet_size[idx])

		return ctx->packet_size[idx];

	else if (ep->sync_source)

		return slave_next_packet_size(ep);

	unsigned int packet;



	packet = ctx->packet_size[idx];

	if (packet) {

		if (avail && packet >= avail)

			return -EAGAIN;

		return packet;

	}



	if (ep->sync_source)

		return slave_next_packet_size(ep, avail);

	else

		return next_packet_size(ep);

		return next_packet_size(ep, avail);

}



static void call_retire_callback(struct snd_usb_endpoint *ep,
@@ -263,7 +284,7 @@ static void prepare_silent_urb(struct snd_usb_endpoint *ep, 
		unsigned int length;

		int counts;



		counts = snd_usb_endpoint_next_packet_size(ep, ctx, i);

		counts = snd_usb_endpoint_next_packet_size(ep, ctx, i, 0);

		length = counts * ep->stride; /* number of silent bytes */

		offset = offs * ep->stride + extra * i;

		urb->iso_frame_desc[i].offset = offset;

sound/usb/endpoint.h

+2 −1
Original line number Diff line number Diff line
@@ -46,6 +46,7 @@ void snd_usb_endpoint_free_all(struct snd_usb_audio *chip); 


int snd_usb_endpoint_implicit_feedback_sink(struct snd_usb_endpoint *ep);

int snd_usb_endpoint_next_packet_size(struct snd_usb_endpoint *ep,

				      struct snd_urb_ctx *ctx, int idx);

				      struct snd_urb_ctx *ctx, int idx,

				      unsigned int avail);



#endif /* __USBAUDIO_ENDPOINT_H */

sound/usb/pcm.c

+1 −1
Original line number Diff line number Diff line
@@ -1365,7 +1365,7 @@ static void prepare_playback_urb(struct snd_usb_substream *subs, 
	spin_lock_irqsave(&subs->lock, flags);

	subs->frame_limit += ep->max_urb_frames;

	for (i = 0; i < ctx->packets; i++) {

		counts = snd_usb_endpoint_next_packet_size(ep, ctx, i);

		counts = snd_usb_endpoint_next_packet_size(ep, ctx, i, 0);

		/* set up descriptor */

		urb->iso_frame_desc[i].offset = frames * stride;

		urb->iso_frame_desc[i].length = counts * stride;