From: Clemens Ladisch <clemens@ladisch.de>
Date: Fri, 12 Aug 2005 06:28:27 +0000 (+0200)
Subject: [ALSA] usb-audio: fix packets per URB calculation for playback
X-Git-Tag: firefly_0821_release~42183^2~52
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=d6db392e9235c48bb945624798e9beede7b85b12;p=firefly-linux-kernel-4.4.55.git

[ALSA] usb-audio: fix packets per URB calculation for playback

USB generic driver
When determining how many packets are needed for one period, we cannot
assume that all packets have their maximum size -- we always use the
nominal sample rate when sending data, and could use an even lower rate
when the endpoint uses frequency feedback.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
---

diff --git a/sound/usb/usbaudio.c b/sound/usb/usbaudio.c
index 9e38d3d1322a..d28106e390c4 100644
--- a/sound/usb/usbaudio.c
+++ b/sound/usb/usbaudio.c
@@ -938,7 +938,15 @@ static int init_substream_urbs(snd_usb_substream_t *subs, unsigned int period_by
 
 	/* decide how many packets to be used */
 	if (is_playback) {
-		total_packs = (period_bytes + maxsize - 1) / maxsize;
+		unsigned int minsize;
+		/* determine how small a packet can be */
+		minsize = (subs->freqn >> (16 - subs->datainterval))
+			  * (frame_bits >> 3);
+		/* with sync from device, assume it can be 25% lower */
+		if (subs->syncpipe)
+			minsize -= minsize >> 2;
+		minsize = max(minsize, 1u);
+		total_packs = (period_bytes + minsize - 1) / minsize;
 		if (total_packs < 2 * MIN_PACKS_URB)
 			total_packs = 2 * MIN_PACKS_URB;
 	} else {