[PATCH 5.15 008/207] ALSA: usb-audio: Avoid killing in-flight URBs during draining

Greg Kroah-Hartman
2021-12-06T15:34:02Z

From: Takashi Iwai <tiwai@suse.de>

commit 813a17cab9b708bbb1e0db8902e19857b57196ec upstream.

While draining a stream, ALSA PCM core stops the stream by issuing
snd_pcm_stop() after all data has been sent out. And, at PCM trigger
stop, currently USB-audio driver kills the in-flight URBs explicitly,
then at sync-stop ops, sync with the finish of all remaining URBs.
This might result in a drop of the drained samples as most of
USB-audio devices / hosts allow relatively long in-flight samples (as
a sort of FIFO).

For avoiding the trimming, this patch changes the stream-stop behavior
during PCM draining state. Under that condition, the pending URBs
won't be killed. The leftover in-flight URBs are caught by the
sync-stop operation that shall be performed after the trigger-stop
operation.

Link: https://lore.kernel.org/r/20210929080844.11583-10-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
sound/usb/endpoint.c | 14 +++++++++-----
sound/usb/endpoint.h | 2 +-
sound/usb/pcm.c | 16 ++++++++--------
3 files changed, 18 insertions(+), 14 deletions(-)

--- a/sound/usb/endpoint.c
+++ b/sound/usb/endpoint.c
@@ -955,7 +955,7 @@ void snd_usb_endpoint_sync_pending_stop(
*
* This function moves the EP to STOPPING state if it's being RUNNING.
*/
-static int stop_urbs(struct snd_usb_endpoint *ep, bool force)
+static int stop_urbs(struct snd_usb_endpoint *ep, bool force, bool keep_pending)
{
unsigned int i;
unsigned long flags;
@@ -972,6 +972,9 @@ static int stop_urbs(struct snd_usb_endp
ep->next_packet_queued = 0;
spin_unlock_irqrestore(&ep->lock, flags);

+ if (keep_pending)
+ return 0;
+
for (i = 0; i < ep->nurbs; i++) {
if (test_bit(i, &ep->active_mask)) {
if (!test_and_set_bit(i, &ep->unlink_mask)) {
@@ -995,7 +998,7 @@ static int release_urbs(struct snd_usb_e
snd_usb_endpoint_set_callback(ep, NULL, NULL, NULL);

/* stop and unlink urbs */
- err = stop_urbs(ep, force);
+ err = stop_urbs(ep, force, false);
if (err)
return err;

@@ -1527,7 +1530,7 @@ int snd_usb_endpoint_start(struct snd_us
return 0;

__error:
- snd_usb_endpoint_stop(ep);
+ snd_usb_endpoint_stop(ep, false);
return -EPIPE;
}

@@ -1535,6 +1538,7 @@ __error:
* snd_usb_endpoint_stop: stop an snd_usb_endpoint
*
* @ep: the endpoint to stop (may be NULL)
+ * @keep_pending: keep in-flight URBs
*
* A call to this function will decrement the running count of the endpoint.
* In case the last user has requested the endpoint stop, the URBs will
@@ -1545,7 +1549,7 @@ __error:
* The caller needs to synchronize the pending stop operation via
* snd_usb_endpoint_sync_pending_stop().
*/
-void snd_usb_endpoint_stop(struct snd_usb_endpoint *ep)
+void snd_usb_endpoint_stop(struct snd_usb_endpoint *ep, bool keep_pending)
{
if (!ep)
return;
@@ -1560,7 +1564,7 @@ void snd_usb_endpoint_stop(struct snd_us
if (!atomic_dec_return(&ep->running)) {
if (ep->sync_source)
WRITE_ONCE(ep->sync_source->sync_sink, NULL);
- stop_urbs(ep, false);
+ stop_urbs(ep, false, keep_pending);
}
}

--- a/sound/usb/endpoint.h
+++ b/sound/usb/endpoint.h
@@ -38,7 +38,7 @@ void snd_usb_endpoint_set_callback(struc
struct snd_usb_substream *data_subs);

int snd_usb_endpoint_start(struct snd_usb_endpoint *ep);
-void snd_usb_endpoint_stop(struct snd_usb_endpoint *ep);
+void snd_usb_endpoint_stop(struct snd_usb_endpoint *ep, bool keep_pending);
void snd_usb_endpoint_sync_pending_stop(struct snd_usb_endpoint *ep);
void snd_usb_endpoint_suspend(struct snd_usb_endpoint *ep);
int snd_usb_endpoint_activate(struct snd_usb_endpoint *ep);
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -219,16 +219,16 @@ int snd_usb_init_pitch(struct snd_usb_au
return 0;
}

-static bool stop_endpoints(struct snd_usb_substream *subs)
+static bool stop_endpoints(struct snd_usb_substream *subs, bool keep_pending)
{
bool stopped = 0;

if (test_and_clear_bit(SUBSTREAM_FLAG_SYNC_EP_STARTED, &subs->flags)) {
- snd_usb_endpoint_stop(subs->sync_endpoint);
+ snd_usb_endpoint_stop(subs->sync_endpoint, keep_pending);
stopped = true;
}
if (test_and_clear_bit(SUBSTREAM_FLAG_DATA_EP_STARTED, &subs->flags)) {
- snd_usb_endpoint_stop(subs->data_endpoint);
+ snd_usb_endpoint_stop(subs->data_endpoint, keep_pending);
stopped = true;
}
return stopped;
@@ -261,7 +261,7 @@ static int start_endpoints(struct snd_us
return 0;

error:
- stop_endpoints(subs);
+ stop_endpoints(subs, false);
return err;
}

@@ -437,7 +437,7 @@ static int configure_endpoints(struct sn

if (subs->data_endpoint->need_setup) {
/* stop any running stream beforehand */
- if (stop_endpoints(subs))
+ if (stop_endpoints(subs, false))
sync_pending_stops(subs);
err = snd_usb_endpoint_configure(chip, subs->data_endpoint);
if (err < 0)
@@ -572,7 +572,7 @@ static int snd_usb_hw_free(struct snd_pc
subs->cur_audiofmt = NULL;
mutex_unlock(&chip->mutex);
if (!snd_usb_lock_shutdown(chip)) {
- if (stop_endpoints(subs))
+ if (stop_endpoints(subs, false))
sync_pending_stops(subs);
close_endpoints(chip, subs);
snd_usb_unlock_shutdown(chip);
@@ -1559,7 +1559,7 @@ static int snd_usb_substream_playback_tr
return 0;
case SNDRV_PCM_TRIGGER_SUSPEND:
case SNDRV_PCM_TRIGGER_STOP:
- stop_endpoints(subs);
+ stop_endpoints(subs, substream->runtime->status->state == SNDRV_PCM_STATE_DRAINING);
snd_usb_endpoint_set_callback(subs->data_endpoint,
NULL, NULL, NULL);
subs->running = 0;
@@ -1607,7 +1607,7 @@ static int snd_usb_substream_capture_tri
return 0;
case SNDRV_PCM_TRIGGER_SUSPEND:
case SNDRV_PCM_TRIGGER_STOP:
- stop_endpoints(subs);
+ stop_endpoints(subs, false);
fallthrough;
case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
snd_usb_endpoint_set_callback(subs->data_endpoint,