Revert "ALSA: usb-audio: Reduce latency at playback start"

This reverts commit 9ce650a75a3b262c90789b42aedee8fc2ee04d53.

This commit causes watchdog lockups on my machine, and while I have no
idea what the cause is, it bisected right to this commit, and reverting
the change promptly fixes it.

At least occasionally one of the watchdog call traces was

  Call Trace:
    _raw_spin_lock_irqsave+0x35/0x40
    snd_pcm_period_elapsed+0x1b/0xa0 [snd_pcm]
    snd_usb_endpoint_start+0x1a0/0x3c0 [snd_usb_audio]
    start_endpoints+0x23/0x90 [snd_usb_audio]
    snd_usb_substream_playback_trigger+0x7b/0x1a0 [snd_usb_audio]
    snd_pcm_common_ioctl+0x1c44/0x2360 [snd_pcm]
    snd_pcm_ioctl+0x2e/0x40 [snd_pcm]
    __se_sys_ioctl+0x72/0xc0
    do_syscall_64+0x4c/0xa0
    entry_SYSCALL_64_after_hwframe+0x44/0xae

so presumably it's a locking error on that substream spinlock that
snd_pcm_period_elapsed() takes.  But at this point I just want to have a
working system so that I can continue the merge window work tomorrow.

Cc: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index c66831ee15f92e225ec4a47572b42dc7d96f4538..e26d37365f0275282a3d3d9f458c153e4549b7b4 100644 (file)
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -613,6 +613,11 @@ static int snd_usb_pcm_prepare(struct snd_pcm_substream *substream)
        subs->last_frame_number = 0;
        runtime->delay = 0;
 
+       /* for playback, submit the URBs now; otherwise, the first hwptr_done
+        * updates for all URBs would happen at the same time when starting */
+       if (subs->direction == SNDRV_PCM_STREAM_PLAYBACK)
+               ret = start_endpoints(subs);
+
  unlock:
        snd_usb_unlock_shutdown(chip);
        return ret;
@@ -1425,7 +1430,6 @@ static int snd_usb_substream_playback_trigger(struct snd_pcm_substream *substrea
                                              int cmd)
 {
        struct snd_usb_substream *subs = substream->runtime->private_data;
-       int err;
 
        switch (cmd) {
        case SNDRV_PCM_TRIGGER_START:
@@ -1436,14 +1440,6 @@ static int snd_usb_substream_playback_trigger(struct snd_pcm_substream *substrea
                                              prepare_playback_urb,
                                              retire_playback_urb,
                                              subs);
-               if (cmd == SNDRV_PCM_TRIGGER_START) {
-                       err = start_endpoints(subs);
-                       if (err < 0) {
-                               snd_usb_endpoint_set_callback(subs->data_endpoint,
-                                                             NULL, NULL, NULL);
-                               return err;
-                       }
-               }
                subs->running = 1;
                dev_dbg(&subs->dev->dev, "%d:%d Start Playback PCM\n",
                        subs->cur_audiofmt->iface,