The recent fix for the hw constraints for implicit feedback streams via commit e4ea77f8e53f ("ALSA: usb-audio: Always apply the hw constraints for implicit fb sync") added the check of the matching endpoints and whether those EPs are already opened. This is needed and correct, per se, even for the normal streams without the implicit feedback, as the endpoint setup is exclusive.

However, it's reported that there seem applications that behave in unexpected ways to update the hw_params without clearing the previous setup via hw_free, and those hit a problem now: then hw_params is called with still the previous EP setup kept, hence it's restricted with the previous own setup. Although the obvious fix is to call snd_pcm_hw_free() API in the application side, it's a kind of unwelcome change.

This patch tries to ease the situation: in the endpoint check, we add a couple of more conditions and now skip the endpoint that is being used only by the stream in question itself. That is, in addition to the presence check of ep (ep->cur_audiofmt is non-NULL), when the following conditions are met, we skip such an ep: - ep->opened == 1, and - ep->cur_audiofmt == subs->cur_audiofmt.

subs->cur_audiofmt is non-NULL only if it's a re-setup of hw_params, and ep->cur_audiofmt points to the currently set up parameters. So if those match, it must be this stream itself.

Fixes: e4ea77f8e53f ("ALSA: usb-audio: Always apply the hw constraints for implicit fb sync") BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=211941 Cc: stable@vger.kernel.org Signed-off-by: Takashi Iwai tiwai@suse.de --- sound/usb/pcm.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c index bf5a0f3c1fad..e5311b6bb3f6 100644 --- a/sound/usb/pcm.c +++ b/sound/usb/pcm.c @@ -845,13 +845,19 @@ get_sync_ep_from_substream(struct snd_usb_substream *subs)

list_for_each_entry(fp, &subs->fmt_list, list) { ep = snd_usb_get_endpoint(chip, fp->endpoint); - if (ep && ep->cur_rate) - return ep; + if (ep && ep->cur_audiofmt) { + /* if EP is already opened solely for this substream, + * we still allow us to change the parameter; otherwise + * this substream has to follow the existing parameter + */ + if (ep->cur_audiofmt != subs->cur_audiofmt || ep->opened > 1) + return ep; + } if (!fp->implicit_fb) continue; /* for the implicit fb, check the sync ep as well */ ep = snd_usb_get_endpoint(chip, fp->sync_ep); - if (ep && ep->cur_rate) + if (ep && ep->cur_audiofmt) return ep; } return NULL;