[alsa-devel] [PATCH sound-unstable] usb-audio: sync ep init fix for audioformat mistmatch

[Eldad Zack]

Commit 947d299686aa9cc8aecf749d54e8475c6e498956 , "ALSA: snd-usb:
properly initialize the sync endpoint", while correcting the
initialization of the sync endpoint when opening just the data
endpoint, prevents devices that has a sync endpoint with a channel
number different than the data endpoint channel from functioning.
Due to a different channel and period bytes count. attempting to
initialize the sync endpoint will fail at the usb host driver:
(example, when using xhci:)

 cannot submit urb 0, error -90: internal error

With this patch, if a sync endpoint has multiple audioformats, a
matching audioformat is perferred. An audioformat must be found
with at least one channel and support the requested sample rate
and PCM format, otherwise the stream will not be opened.

If the number of channels differ between the selected audioformat
and the requested format, adjust the period bytes count accordingly.
It is safe to perform the calculation on the basis of the channel
count, since the PCM audio format and the rate must be supported by
the selected audioformat.

Cc: Jeffrey Barish <jeff_barish at earthlink.net>
Cc: Daniel Mack <zonque at gmail.com>
Signed-off-by: Eldad Zack <eldad at fogrefinery.com>
---
 sound/usb/pcm.c |  106 +++++++++++++++++++++++++++++++++++++++++++++++++++----
 1 files changed, 99 insertions(+), 7 deletions(-)

diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index 5d3cf85..e539a5a 100644
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -451,6 +451,103 @@ add_sync_ep:
 }
 
 /*
+ * Return the score of matching two audioformats.
+ * Veto the audioformat if:
+ * - It has no channels for some reason.
+ * - Requested PCM format is not supported.
+ * - Requested sample rate is not supported.
+ */
+static int match_endpoint_audioformats(struct audioformat *fp,
+	struct audioformat *match, int rate,
+	snd_pcm_format_t pcm_format)
+{
+	int i;
+	int score = 0;
+
+	if (fp->channels < 1) {
+		snd_printdd("%s: (fmt @%p) no channels\n", __func__, fp);
+		return 0;
+	}
+
+	if (!(fp->formats && pcm_format)) {
+		snd_printdd("%s: (fmt @%p) no match for format %d\n", __func__,
+			fp, pcm_format);
+		return 0;
+	}
+
+	for (i = 0; i < 4; i++) {
+		if (fp->rate_table[i] == rate) {
+			score++;
+			break;
+		}
+	}
+	if (!score) {
+		snd_printdd("%s: (fmt @%p) no match for rate %d\n", __func__,
+			fp, rate);
+		return 0;
+	}
+
+	if (fp->channels == match->channels)
+		score++;
+
+	snd_printdd("%s: (fmt @%p) score %d\n", __func__, fp, score);
+
+	return score;
+}
+
+/*
+ * Configure the sync ep using the rate and pcm format of the data ep.
+ */
+static int configure_sync_endpoint(struct snd_usb_substream *subs)
+{
+	int ret;
+	struct audioformat *fp;
+	struct audioformat *sync_fp = NULL;
+	int cur_score = 0;
+	int sync_period_bytes = subs->period_bytes;
+	struct snd_usb_substream *sync_subs =
+		&subs->stream->substream[subs->direction ^ 1];
+
+	/* Try to find the best matching audioformat. */
+	list_for_each_entry(fp, &sync_subs->fmt_list, list) {
+		int score = match_endpoint_audioformats(fp, subs->cur_audiofmt,
+			subs->cur_rate, subs->pcm_format);
+
+		if (score > cur_score) {
+			sync_fp = fp;
+			cur_score = score;
+		}
+	}
+
+	if (unlikely(sync_fp == NULL)) {
+		snd_printk(KERN_ERR "%s: no valid audioformat for sync ep %x found\n",
+			__func__, sync_subs->ep_num);
+		return -EINVAL;
+	}
+
+	/*
+	 * Recalculated the period bytes if channel number differ between
+	 * data and sync ep audioformat.
+	 */
+	if (sync_fp->channels != subs->channels) {
+		sync_period_bytes = (subs->period_bytes / subs->channels) *
+			sync_fp->channels;
+		snd_printdd("%s: adjusted sync ep period bytes (%d -> %d)\n",
+			__func__, subs->period_bytes, sync_period_bytes);
+	}
+
+	ret = snd_usb_endpoint_set_params(subs->sync_endpoint,
+					  subs->pcm_format,
+					  sync_fp->channels,
+					  sync_period_bytes,
+					  subs->cur_rate,
+					  sync_fp,
+					  NULL);
+
+	return ret;
+}
+
+/*
  * configure endpoint params
  *
  * called  during initial setup and upon resume
@@ -472,13 +569,8 @@ static int configure_endpoint(struct snd_usb_substream *subs)
 		return ret;
 
 	if (subs->sync_endpoint)
-		ret = snd_usb_endpoint_set_params(subs->sync_endpoint,
-						  subs->pcm_format,
-						  subs->channels,
-						  subs->period_bytes,
-						  subs->cur_rate,
-						  subs->cur_audiofmt,
-						  NULL);
+		ret = configure_sync_endpoint(subs);
+
 	return ret;
 }
 
-- 
1.7.8.6