[ALSA] usb-audio - use only one packet in synchronization feedback URBs

USB generic driver
Do not use more than one packet in synchronization feedback URBs because
it would be pointless to send or receive more than one value at the same
time.
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>

sound/usb/usbaudio.c

@@ -177,7 +177,7 @@ struct snd_usb_substream {
 	unsigned int nurbs;			/* # urbs */
 	snd_urb_ctx_t dataurb[MAX_URBS];	/* data urb table */
 	snd_urb_ctx_t syncurb[SYNC_URBS];	/* sync urb table */
-	char syncbuf[SYNC_URBS * MAX_PACKS * 4]; /* sync buffer; it's so small - let's get static */
+	char syncbuf[SYNC_URBS * 4];	/* sync buffer; it's so small - let's get static */
 	char *tmpbuf;			/* temporary buffer for playback */
 
 	u64 formats;			/* format bitmasks (all or'ed) */
@@ -251,17 +251,13 @@ static int prepare_capture_sync_urb(snd_usb_substream_t *subs,
 {
 	unsigned char *cp = urb->transfer_buffer;
 	snd_urb_ctx_t *ctx = (snd_urb_ctx_t *)urb->context;
-	int i, offs;
 
-	urb->number_of_packets = ctx->packets;
 	urb->dev = ctx->subs->dev; /* we need to set this at each time */
-	for (i = offs = 0; i < urb->number_of_packets; i++, offs += 4, cp += 4) {
-		urb->iso_frame_desc[i].length = 3;
-		urb->iso_frame_desc[i].offset = offs;
-		cp[0] = subs->freqn >> 2;
-		cp[1] = subs->freqn >> 10;
-		cp[2] = subs->freqn >> 18;
-	}
+	urb->iso_frame_desc[0].length = 3;
+	urb->iso_frame_desc[0].offset = 0;
+	cp[0] = subs->freqn >> 2;
+	cp[1] = subs->freqn >> 10;
+	cp[2] = subs->freqn >> 18;
 	return 0;
 }
 
@@ -277,18 +273,14 @@ static int prepare_capture_sync_urb_hs(snd_usb_substream_t *subs,
 {
 	unsigned char *cp = urb->transfer_buffer;
 	snd_urb_ctx_t *ctx = (snd_urb_ctx_t *)urb->context;
-	int i, offs;
 
-	urb->number_of_packets = ctx->packets;
 	urb->dev = ctx->subs->dev; /* we need to set this at each time */
-	for (i = offs = 0; i < urb->number_of_packets; i++, offs += 4, cp += 4) {
-		urb->iso_frame_desc[i].length = 4;
-		urb->iso_frame_desc[i].offset = offs;
-		cp[0] = subs->freqn;
-		cp[1] = subs->freqn >> 8;
-		cp[2] = subs->freqn >> 16;
-		cp[3] = subs->freqn >> 24;
-	}
+	urb->iso_frame_desc[0].length = 4;
+	urb->iso_frame_desc[0].offset = 0;
+	cp[0] = subs->freqn;
+	cp[1] = subs->freqn >> 8;
+	cp[2] = subs->freqn >> 16;
+	cp[3] = subs->freqn >> 24;
 	return 0;
 }
 
@@ -418,15 +410,11 @@ static int prepare_playback_sync_urb(snd_usb_substream_t *subs,
 				     snd_pcm_runtime_t *runtime,
 				     struct urb *urb)
 {
-	int i, offs;
 	snd_urb_ctx_t *ctx = (snd_urb_ctx_t *)urb->context;
 
-	urb->number_of_packets = ctx->packets;
 	urb->dev = ctx->subs->dev; /* we need to set this at each time */
-	for (i = offs = 0; i < urb->number_of_packets; i++, offs += 4) {
-		urb->iso_frame_desc[i].length = 3;
-		urb->iso_frame_desc[i].offset = offs;
-	}
+	urb->iso_frame_desc[0].length = 3;
+	urb->iso_frame_desc[0].offset = 0;
 	return 0;
 }
 
@@ -440,15 +428,11 @@ static int prepare_playback_sync_urb_hs(snd_usb_substream_t *subs,
 					snd_pcm_runtime_t *runtime,
 					struct urb *urb)
 {
-	int i, offs;
 	snd_urb_ctx_t *ctx = (snd_urb_ctx_t *)urb->context;
 
-	urb->number_of_packets = ctx->packets;
 	urb->dev = ctx->subs->dev; /* we need to set this at each time */
-	for (i = offs = 0; i < urb->number_of_packets; i++, offs += 4) {
-		urb->iso_frame_desc[i].length = 4;
-		urb->iso_frame_desc[i].offset = offs;
-	}
+	urb->iso_frame_desc[0].length = 4;
+	urb->iso_frame_desc[0].offset = 0;
 	return 0;
 }
 
@@ -462,17 +446,12 @@ static int retire_playback_sync_urb(snd_usb_substream_t *subs,
 				    snd_pcm_runtime_t *runtime,
 				    struct urb *urb)
 {
-	int i;
-	unsigned int f, found;
-	unsigned char *cp = urb->transfer_buffer;
+	unsigned int f;
 	unsigned long flags;
 
-	found = 0;
-	for (i = 0; i < urb->number_of_packets; i++, cp += 4) {
-		if (urb->iso_frame_desc[i].status ||
-		    urb->iso_frame_desc[i].actual_length < 3)
-			continue;
-		f = combine_triple(cp) << 2;
+	if (urb->iso_frame_desc[0].status == 0 &&
+	    urb->iso_frame_desc[0].actual_length == 3) {
+		f = combine_triple((u8*)urb->transfer_buffer) << 2;
 #if 0
 		if (f < subs->freqn - (subs->freqn>>3) || f > subs->freqmax) {
 			snd_printd(KERN_WARNING "requested frequency %d (%u,%03uHz) out of range (current nominal %d (%u,%03uHz))\n",
@@ -481,11 +460,8 @@ static int retire_playback_sync_urb(snd_usb_substream_t *subs,
 			continue;
 		}
 #endif
-		found = f;
-	}
-	if (found) {
 		spin_lock_irqsave(&subs->lock, flags);
-		subs->freqm = found;
+		subs->freqm = f;
 		spin_unlock_irqrestore(&subs->lock, flags);
 	}
 
@@ -502,21 +478,14 @@ static int retire_playback_sync_urb_hs(snd_usb_substream_t *subs,
 				       snd_pcm_runtime_t *runtime,
 				       struct urb *urb)
 {
-	int i;
-	unsigned int found;
-	unsigned char *cp = urb->transfer_buffer;
+	unsigned int f;
 	unsigned long flags;
 
-	found = 0;
-	for (i = 0; i < urb->number_of_packets; i++, cp += 4) {
-		if (urb->iso_frame_desc[i].status ||
-		    urb->iso_frame_desc[i].actual_length < 4)
-			continue;
-		found = combine_quad(cp) & 0x0fffffff;
-	}
-	if (found) {
+	if (urb->iso_frame_desc[0].status == 0 &&
+	    urb->iso_frame_desc[0].actual_length == 4) {
+		f = combine_quad((u8*)urb->transfer_buffer) & 0x0fffffff;
 		spin_lock_irqsave(&subs->lock, flags);
-		subs->freqm = found;
+		subs->freqm = f;
 		spin_unlock_irqrestore(&subs->lock, flags);
 	}
 
@@ -1039,18 +1008,18 @@ static int init_substream_urbs(snd_usb_substream_t *subs, unsigned int period_by
 			snd_urb_ctx_t *u = &subs->syncurb[i];
 			u->index = i;
 			u->subs = subs;
-			u->packets = nrpacks;
-			u->urb = usb_alloc_urb(u->packets, GFP_KERNEL);
+			u->packets = 1;
+			u->urb = usb_alloc_urb(1, GFP_KERNEL);
 			if (! u->urb) {
 				release_substream_urbs(subs, 0);
 				return -ENOMEM;
 			}
-			u->urb->transfer_buffer = subs->syncbuf + i * nrpacks * 4;
-			u->urb->transfer_buffer_length = nrpacks * 4;
+			u->urb->transfer_buffer = subs->syncbuf + i * 4;
+			u->urb->transfer_buffer_length = 4;
 			u->urb->dev = subs->dev;
 			u->urb->pipe = subs->syncpipe;
 			u->urb->transfer_flags = URB_ISO_ASAP;
-			u->urb->number_of_packets = u->packets;
+			u->urb->number_of_packets = 1;
 			u->urb->interval = 1 << subs->syncinterval;
 			u->urb->context = u;
 			u->urb->complete = snd_usb_complete_callback(snd_complete_sync_urb);