[PATCH v4 2/5] ALSA: usb-audio: Choose audioformat of a counter-part substream

[Takashi Iwai]

The implicit feedback mode needs to handle two endpoints and the
choice of the audioformat object for the sync EP is important since
this determines the compatibility of the hw_params.  The current code
uses the same audioformat object if both the main EP and the sync EP
point to the same iface/altsetting.  This was done in consideration of
the non-implicit-fb sync EP handling, and it doesn't match well with
the cases where actually to endpoints are defined in the sameiface /
altsetting like a few Pioneer devices.

Modify snd_usb_find_implicit_fb_sync_format() to pick up the
audioformat that is assigned in the counter-part substreams primarily,
so that the actual capture stream can be opened properly.  We keep the
same audioformat object only as a fallback in case nothing found,
though.

Fixes: 9fddc15e8039 ("ALSA: usb-audio: Factor out the implicit feedback quirk code")
Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 sound/usb/implicit.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/sound/usb/implicit.c b/sound/usb/implicit.c
index 931042a6a051..9724efe1cdce 100644
--- a/sound/usb/implicit.c
+++ b/sound/usb/implicit.c
@@ -378,20 +378,19 @@ snd_usb_find_implicit_fb_sync_format(struct snd_usb_audio *chip,
 				     int stream)
 {
 	struct snd_usb_substream *subs;
-	const struct audioformat *fp, *sync_fmt;
+	const struct audioformat *fp, *sync_fmt = NULL;
 	int score, high_score;
 
-	/* When sharing the same altset, use the original audioformat */
+	/* Use the original audioformat as fallback for the shared altset */
 	if (target->iface == target->sync_iface &&
 	    target->altsetting == target->sync_altsetting)
-		return target;
+		sync_fmt = target;
 
 	subs = find_matching_substream(chip, stream, target->sync_ep,
 				       target->fmt_type);
 	if (!subs)
-		return NULL;
+		return sync_fmt;
 
-	sync_fmt = NULL;
 	high_score = 0;
 	list_for_each_entry(fp, &subs->fmt_list, list) {
 		score = match_endpoint_audioformats(subs, fp,
-- 
2.26.2