[PATCH 5.15 005/207] ALSA: usb-audio: Check available frames for the next packet size

Greg Kroah-Hartman
2021-12-06T15:32:33Z

From: Takashi Iwai <tiwai@suse.de>

commit d215f63d49da9a8803af3e81acd6cad743686573 upstream.

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: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
sound/usb/endpoint.c | 51 ++++++++++++++++++++++++++++++++++++---------------
sound/usb/endpoint.h | 3 ++-
sound/usb/pcm.c | 2 +-
3 files changed, 39 insertions(+), 17 deletions(-)

--- a/sound/usb/endpoint.c
+++ b/sound/usb/endpoint.c
@@ -148,18 +148,23 @@ int snd_usb_endpoint_implicit_feedback_s
* 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
* 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_u
/*
* 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 sn
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;
--- a/sound/usb/endpoint.h
+++ b/sound/usb/endpoint.h
@@ -46,6 +46,7 @@ void snd_usb_endpoint_free_all(struct sn

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 */
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -1365,7 +1365,7 @@ static void prepare_playback_urb(struct
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;